Intel® 64 and IA-32 Architectures Software

Intel® 64 and IA-32 Architectures
Software Developer’s Manual
Volume 3A:
System Programming Guide, Part 1
NOTE: The Intel® 64 and IA-32 Architectures Software Developer's Manual consists of seven volumes:
Basic Architecture, Order Number 253665; Instruction Set Reference A-L, Order Number 253666;
Instruction Set Reference M-Z, Order Number 253667; Instruction Set Reference, Order Number
326018; System Programming Guide, Part 1, Order Number 253668; System Programming Guide, Part
2, Order Number 253669; System Programming Guide, Part 3, Order Number 326019. Refer to all seven
volumes when evaluating your design needs.
Order Number: 253668-045US
January 2013
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CONTENTS
PAGE
CHAPTER 1
ABOUT THIS MANUAL
1.1
1.2
1.3
1.3.1
1.3.2
1.3.3
1.3.4
1.3.5
1.3.6
1.3.7
1.4
INTEL® 64 AND IA-32 PROCESSORS COVERED IN THIS MANUAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
OVERVIEW OF THE SYSTEM PROGRAMMING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
NOTATIONAL CONVENTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bit and Byte Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reserved Bits and Software Compatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Instruction Operands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hexadecimal and Binary Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Segmented Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Syntax for CPUID, CR, and MSR Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RELATED LITERATURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1-1
1-3
1-5
1-5
1-5
1-6
1-6
1-6
1-7
1-8
1-8
CHAPTER 2
SYSTEM ARCHITECTURE OVERVIEW
2.1
2.1.1
2.1.1.1
2.1.2
2.1.2.1
2.1.3
2.1.3.1
2.1.4
2.1.4.1
2.1.5
2.1.5.1
2.1.6
2.1.6.1
2.1.7
2.2
2.2.1
2.3
2.3.1
2.4
2.4.1
2.4.2
2.4.3
2.4.4
2.5
2.5.1
2.6
2.7
2.7.1
2.7.2
2.7.3
2.7.4
2.7.5
2.7.6
2.7.6.1
2.7.7
2.7.7.1
2.7.8
OVERVIEW OF THE SYSTEM-LEVEL ARCHITECTURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Global and Local Descriptor Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
Global and Local Descriptor Tables in IA-32e Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
System Segments, Segment Descriptors, and Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Gates in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Task-State Segments and Task Gates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Task-State Segments in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Interrupt and Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Interrupt and Exception Handling IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Memory Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
Memory Management in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
System Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
System Registers in IA-32e Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
Other System Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
MODES OF OPERATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
Extended Feature Enable Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
SYSTEM FLAGS AND FIELDS IN THE EFLAGS REGISTER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
System Flags and Fields in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11
MEMORY-MANAGEMENT REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11
Global Descriptor Table Register (GDTR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12
Local Descriptor Table Register (LDTR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12
IDTR Interrupt Descriptor Table Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12
Task Register (TR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
CONTROL REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
CPUID Qualification of Control Register Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-18
EXTENDED CONTROL REGISTERS (INCLUDING XCR0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19
SYSTEM INSTRUCTION SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19
Loading and Storing System Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21
Verifying of Access Privileges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21
Loading and Storing Debug Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22
Invalidating Caches and TLBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22
Controlling the Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23
Reading Performance-Monitoring and Time-Stamp Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23
Reading Counters in 64-Bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-24
Reading and Writing Model-Specific Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-24
Reading and Writing Model-Specific Registers in 64-Bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-24
Enabling Processor Extended States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-24
CHAPTER 3
PROTECTED-MODE MEMORY MANAGEMENT
3.1
3.2
MEMORY MANAGEMENT OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
USING SEGMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Vol. 3A iii
CONTENTS
PAGE
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.3
3.3.1
3.4
3.4.1
3.4.2
3.4.3
3.4.4
3.4.5
3.4.5.1
3.5
3.5.1
3.5.2
Basic Flat Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
Protected Flat Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
Multi-Segment Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Segmentation in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
Paging and Segmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
PHYSICAL ADDRESS SPACE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Intel® 64 Processors and Physical Address Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
LOGICAL AND LINEAR ADDRESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Logical Address Translation in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Segment Selectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Segment Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
Segment Loading Instructions in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
Segment Descriptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
Code- and Data-Segment Descriptor Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12
SYSTEM DESCRIPTOR TYPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
Segment Descriptor Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14
Segment Descriptor Tables in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16
CHAPTER 4
PAGING
4.1
4.1.1
4.1.2
4.1.3
4.1.4
4.2
4.3
4.4
4.4.1
4.4.2
4.5
4.6
4.7
4.8
4.9
4.9.1
4.9.2
4.9.3
4.10
4.10.1
4.10.2
4.10.2.1
4.10.2.2
4.10.2.3
4.10.2.4
4.10.3
4.10.3.1
4.10.3.2
4.10.3.3
4.10.4
4.10.4.1
4.10.4.2
4.10.4.3
4.10.4.4
4.10.5
4.11
4.11.1
4.11.2
4.12
4.13
PAGING MODES AND CONTROL BITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Three Paging Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Paging-Mode Enabling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
Paging-Mode Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
Enumeration of Paging Features by CPUID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
HIERARCHICAL PAGING STRUCTURES: AN OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
32-BIT PAGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7
PAE PAGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13
PDPTE Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13
Linear-Address Translation with PAE Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14
IA-32E PAGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19
ACCESS RIGHTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-28
PAGE-FAULT EXCEPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-30
ACCESSED AND DIRTY FLAGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-31
PAGING AND MEMORY TYPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-31
Paging and Memory Typing When the PAT is Not Supported (Pentium Pro and Pentium II Processors) . . . . . . . . . . . . . . 4-31
Paging and Memory Typing When the PAT is Supported (Pentium III and More Recent Processor Families). . . . . . . . . . 4-32
Caching Paging-Related Information about Memory Typing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-32
CACHING TRANSLATION INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-33
Process-Context Identifiers (PCIDs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-33
Translation Lookaside Buffers (TLBs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-33
Page Numbers, Page Frames, and Page Offsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-34
Caching Translations in TLBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-34
Details of TLB Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-35
Global Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-35
Paging-Structure Caches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-35
Caches for Paging Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-35
Using the Paging-Structure Caches to Translate Linear Addresses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-37
Multiple Cached Entries for a Single Paging-Structure Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-38
Invalidation of TLBs and Paging-Structure Caches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-38
Operations that Invalidate TLBs and Paging-Structure Caches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-38
Recommended Invalidation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-40
Optional Invalidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-41
Delayed Invalidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-42
Propagation of Paging-Structure Changes to Multiple Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-43
INTERACTIONS WITH VIRTUAL-MACHINE EXTENSIONS (VMX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44
VMX Transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44
VMX Support for Address Translation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44
USING PAGING FOR VIRTUAL MEMORY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44
MAPPING SEGMENTS TO PAGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-45
iv Vol. 3A
CONTENTS
PAGE
CHAPTER 5
PROTECTION
5.1
5.2
5.2.1
5.3
5.3.1
5.4
5.4.1
5.4.1.1
5.5
5.6
5.6.1
5.7
5.8
5.8.1
5.8.1.1
5.8.1.2
5.8.2
5.8.3
5.8.3.1
5.8.4
5.8.5
5.8.5.1
5.8.6
5.8.7
5.8.7.1
5.8.8
5.9
5.10
5.10.1
5.10.2
5.10.3
5.10.4
5.10.5
5.11
5.11.1
5.11.2
5.11.3
5.11.4
5.11.5
5.12
5.13
5.13.1
5.13.2
5.13.3
5.13.4
ENABLING AND DISABLING SEGMENT AND PAGE PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
FIELDS AND FLAGS USED FOR SEGMENT-LEVEL AND
PAGE-LEVEL PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2
Code Segment Descriptor in 64-bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
LIMIT CHECKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
Limit Checking in 64-bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
TYPE CHECKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
Null Segment Selector Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
NULL Segment Checking in 64-bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
PRIVILEGE LEVELS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
PRIVILEGE LEVEL CHECKING WHEN ACCESSING DATA SEGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8
Accessing Data in Code Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
PRIVILEGE LEVEL CHECKING WHEN LOADING THE SS REGISTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10
PRIVILEGE LEVEL CHECKING WHEN TRANSFERRING PROGRAM CONTROL BETWEEN CODE SEGMENTS . . . . . . . . . . . . . . . . 5-10
Direct Calls or Jumps to Code Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10
Accessing Nonconforming Code Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11
Accessing Conforming Code Segments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12
Gate Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13
Call Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13
IA-32e Mode Call Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14
Accessing a Code Segment Through a Call Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15
Stack Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17
Stack Switching in 64-bit Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19
Returning from a Called Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20
Performing Fast Calls to System Procedures with the
SYSENTER and SYSEXIT Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20
SYSENTER and SYSEXIT Instructions in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-21
Fast System Calls in 64-Bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22
PRIVILEGED INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23
POINTER VALIDATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24
Checking Access Rights (LAR Instruction) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24
Checking Read/Write Rights (VERR and VERW Instructions) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25
Checking That the Pointer Offset Is Within Limits (LSL Instruction) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25
Checking Caller Access Privileges (ARPL Instruction) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26
Checking Alignment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-27
PAGE-LEVEL PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-27
Page-Protection Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28
Restricting Addressable Domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28
Page Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28
Combining Protection of Both Levels of Page Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28
Overrides to Page Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29
COMBINING PAGE AND SEGMENT PROTECTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29
PAGE-LEVEL PROTECTION AND EXECUTE-DISABLE BIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30
Detecting and Enabling the Execute-Disable Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30
Execute-Disable Page Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30
Reserved Bit Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31
Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32
CHAPTER 6
INTERRUPT AND EXCEPTION HANDLING
6.1
6.2
6.3
6.3.1
6.3.2
6.3.3
6.4
6.4.1
6.4.2
6.4.3
6.5
INTERRUPT AND EXCEPTION OVERVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EXCEPTION AND INTERRUPT VECTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SOURCES OF INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Maskable Hardware Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Software-Generated Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SOURCES OF EXCEPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Program-Error Exceptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Software-Generated Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Machine-Check Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EXCEPTION CLASSIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6-1
6-1
6-2
6-2
6-3
6-4
6-4
6-4
6-4
6-4
6-4
Vol. 3A v
CONTENTS
PAGE
6.6
6.7
6.7.1
6.8
6.8.1
6.8.2
6.8.3
6.9
6.10
6.11
6.12
6.12.1
6.12.1.1
6.12.1.2
6.12.2
6.13
6.14
6.14.1
6.14.2
6.14.3
6.14.4
6.14.5
6.15
PROGRAM OR TASK RESTART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5
NONMASKABLE INTERRUPT (NMI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6
Handling Multiple NMIs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6
ENABLING AND DISABLING INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6
Masking Maskable Hardware Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6
Masking Instruction Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7
Masking Exceptions and Interrupts When Switching Stacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7
PRIORITY AMONG SIMULTANEOUS EXCEPTIONS AND INTERRUPTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8
INTERRUPT DESCRIPTOR TABLE (IDT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9
IDT DESCRIPTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10
EXCEPTION AND INTERRUPT HANDLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11
Exception- or Interrupt-Handler Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11
Protection of Exception- and Interrupt-Handler Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13
Flag Usage By Exception- or Interrupt-Handler Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14
Interrupt Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14
ERROR CODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15
EXCEPTION AND INTERRUPT HANDLING IN 64-BIT MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16
64-Bit Mode IDT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16
64-Bit Mode Stack Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17
IRET in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18
Stack Switching in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18
Interrupt Stack Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-19
EXCEPTION AND INTERRUPT REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-19
Interrupt 0—Divide Error Exception (#DE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-20
Interrupt 1—Debug Exception (#DB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21
Interrupt 2—NMI Interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22
Interrupt 3—Breakpoint Exception (#BP). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-23
Interrupt 4—Overflow Exception (#OF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-24
Interrupt 5—BOUND Range Exceeded Exception (#BR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-25
Interrupt 6—Invalid Opcode Exception (#UD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-26
Interrupt 7—Device Not Available Exception (#NM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-27
Interrupt 8—Double Fault Exception (#DF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28
Interrupt 9—Coprocessor Segment Overrun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-30
Interrupt 10—Invalid TSS Exception (#TS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-31
Interrupt 11—Segment Not Present (#NP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-34
Interrupt 12—Stack Fault Exception (#SS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-36
Interrupt 13—General Protection Exception (#GP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-37
Interrupt 14—Page-Fault Exception (#PF). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-40
Interrupt 16—x87 FPU Floating-Point Error (#MF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-43
Interrupt 17—Alignment Check Exception (#AC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-45
Interrupt 18—Machine-Check Exception (#MC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-47
Interrupt 19—SIMD Floating-Point Exception (#XM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-48
Interrupt 20—Virtualization Exception (#VE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-50
Interrupts 32 to 255—User Defined Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-51
CHAPTER 7
TASK MANAGEMENT
7.1
7.1.1
7.1.2
7.1.3
7.2
7.2.1
7.2.2
7.2.3
7.2.4
7.2.5
7.3
7.4
7.4.1
7.4.2
TASK MANAGEMENT OVERVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
Task Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
Task State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2
Executing a Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2
TASK MANAGEMENT DATA STRUCTURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3
Task-State Segment (TSS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3
TSS Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5
TSS Descriptor in 64-bit mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6
Task Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7
Task-Gate Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8
TASK SWITCHING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9
TASK LINKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12
Use of Busy Flag To Prevent Recursive Task Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13
Modifying Task Linkages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13
vi Vol. 3A
CONTENTS
PAGE
7.5
7.5.1
7.5.2
7.6
7.7
TASK ADDRESS SPACE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14
Mapping Tasks to the Linear and Physical Address Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14
Task Logical Address Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15
16-BIT TASK-STATE SEGMENT (TSS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15
TASK MANAGEMENT IN 64-BIT MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16
CHAPTER 8
MULTIPLE-PROCESSOR MANAGEMENT
8.1
8.1.1
8.1.2
8.1.2.1
8.1.2.2
8.1.3
8.1.4
8.2
8.2.1
8.2.2
8.2.3
8.2.3.1
8.2.3.2
8.2.3.3
8.2.3.4
8.2.3.5
8.2.3.6
8.2.3.7
8.2.3.8
8.2.3.9
8.2.4
8.2.4.1
8.2.4.2
8.2.5
8.3
8.4
8.4.1
8.4.2
8.4.3
8.4.4
8.4.4.1
8.4.4.2
8.4.5
8.5
8.6
8.6.1
8.6.2
8.6.3
8.6.4
8.7
8.7.1
8.7.2
8.7.3
8.7.4
8.7.5
8.7.6
8.7.7
8.7.8
8.7.9
8.7.10
8.7.11
8.7.12
8.7.13
8.7.13.1
8.7.13.2
8.7.13.3
LOCKED ATOMIC OPERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
Guaranteed Atomic Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2
Bus Locking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3
Automatic Locking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3
Software Controlled Bus Locking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3
Handling Self- and Cross-Modifying Code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4
Effects of a LOCK Operation on Internal Processor Caches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5
MEMORY ORDERING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5
Memory Ordering in the Intel® Pentium® and Intel486™ Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6
Memory Ordering in P6 and More Recent Processor Families . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6
Examples Illustrating the Memory-Ordering Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7
Assumptions, Terminology, and Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8
Neither Loads Nor Stores Are Reordered with Like Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8
Stores Are Not Reordered With Earlier Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9
Loads May Be Reordered with Earlier Stores to Different Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9
Intra-Processor Forwarding Is Allowed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-10
Stores Are Transitively Visible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-10
Stores Are Seen in a Consistent Order by Other Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11
Locked Instructions Have a Total Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11
Loads and Stores Are Not Reordered with Locked Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11
Fast-String Operation and Out-of-Order Stores. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12
Memory-Ordering Model for String Operations on Write-Back (WB) Memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12
Examples Illustrating Memory-Ordering Principles for String Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-13
Strengthening or Weakening the Memory-Ordering Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-15
SERIALIZING INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16
MULTIPLE-PROCESSOR (MP) INITIALIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18
BSP and AP Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18
MP Initialization Protocol Requirements and Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18
MP Initialization Protocol Algorithm for Intel Xeon Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-19
MP Initialization Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20
Typical BSP Initialization Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20
Typical AP Initialization Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22
Identifying Logical Processors in an MP System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22
INTEL® HYPER-THREADING TECHNOLOGY AND INTEL® MULTI-CORE TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-24
DETECTING HARDWARE MULTI-THREADING SUPPORT AND TOPOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-24
Initializing Processors Supporting Hyper-Threading Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-25
Initializing Multi-Core Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-25
Executing Multiple Threads on an Intel® 64 or IA-32 Processor Supporting Hardware Multi-Threading . . . . . . . . . . . . 8-25
Handling Interrupts on an IA-32 Processor Supporting Hardware Multi-Threading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-25
INTEL® HYPER-THREADING TECHNOLOGY ARCHITECTURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-26
State of the Logical Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-27
APIC Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28
Memory Type Range Registers (MTRR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28
Page Attribute Table (PAT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28
Machine Check Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28
Debug Registers and Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29
Performance Monitoring Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29
IA32_MISC_ENABLE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29
Memory Ordering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29
Serializing Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29
Microcode Update Resources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29
Self Modifying Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30
Implementation-Specific Intel HT Technology Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30
Processor Caches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30
Processor Translation Lookaside Buffers (TLBs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30
Thermal Monitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-31
Vol. 3A vii
CONTENTS
PAGE
8.7.13.4
8.8
8.8.1
8.8.2
8.8.3
8.8.4
8.8.5
8.9
8.9.1
8.9.2
8.9.3
8.9.3.1
8.9.4
8.9.5
8.10
8.10.1
8.10.2
8.10.3
8.10.4
8.10.5
8.10.6
8.10.6.1
8.10.6.2
8.10.6.3
8.10.6.4
8.10.6.5
8.10.6.6
8.10.6.7
8.11
8.11.1
8.11.2
8.11.2.1
External Signal Compatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-31
MULTI-CORE ARCHITECTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-31
Logical Processor Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32
Memory Type Range Registers (MTRR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32
Performance Monitoring Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32
IA32_MISC_ENABLE MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32
Microcode Update Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32
PROGRAMMING CONSIDERATIONS FOR HARDWARE MULTI-THREADING CAPABLE PROCESSORS . . . . . . . . . . . . . . . . . . . . . 8-33
Hierarchical Mapping of Shared Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-33
Hierarchical Mapping of CPUID Extended Topology Leaf. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-34
Hierarchical ID of Logical Processors in an MP System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-35
Hierarchical ID of Logical Processors with x2APIC ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-37
Algorithm for Three-Level Mappings of APIC_ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-37
Identifying Topological Relationships in a MP System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-42
MANAGEMENT OF IDLE AND BLOCKED CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-46
HLT Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-46
PAUSE Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-46
Detecting Support MONITOR/MWAIT Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-46
MONITOR/MWAIT Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-47
Monitor/Mwait Address Range Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-48
Required Operating System Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-48
Use the PAUSE Instruction in Spin-Wait Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-49
Potential Usage of MONITOR/MWAIT in C0 Idle Loops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-49
Halt Idle Logical Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-50
Potential Usage of MONITOR/MWAIT in C1 Idle Loops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-51
Guidelines for Scheduling Threads on Logical Processors Sharing Execution Resources . . . . . . . . . . . . . . . . . . . . . . . . . 8-51
Eliminate Execution-Based Timing Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-52
Place Locks and Semaphores in Aligned, 128-Byte Blocks of Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-52
MP INITIALIZATION FOR P6 FAMILY PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-52
Overview of the MP Initialization Process For P6 Family Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-52
MP Initialization Protocol Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-53
Error Detection and Handling During the MP Initialization Protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-54
CHAPTER 9
PROCESSOR MANAGEMENT AND INITIALIZATION
9.1
9.1.1
9.1.2
9.1.3
9.1.4
9.2
9.2.1
9.2.2
9.3
9.4
9.5
9.6
9.7
9.7.1
9.7.2
9.8
9.8.1
9.8.2
9.8.3
9.8.4
9.8.5
9.8.5.1
9.8.5.2
9.8.5.3
9.8.5.4
9.9
9.9.1
9.9.2
9.10
INITIALIZATION OVERVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1
Processor State After Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2
Processor Built-In Self-Test (BIST) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2
Model and Stepping Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4
First Instruction Executed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5
X87 FPU INITIALIZATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5
Configuring the x87 FPU Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5
Setting the Processor for x87 FPU Software Emulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-6
CACHE ENABLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7
MODEL-SPECIFIC REGISTERS (MSRS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7
MEMORY TYPE RANGE REGISTERS (MTRRS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7
INITIALIZING SSE/SSE2/SSE3/SSSE3 EXTENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8
SOFTWARE INITIALIZATION FOR REAL-ADDRESS MODE OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8
Real-Address Mode IDT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8
NMI Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8
SOFTWARE INITIALIZATION FOR PROTECTED-MODE OPERATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9
Protected-Mode System Data Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9
Initializing Protected-Mode Exceptions and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10
Initializing Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10
Initializing Multitasking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10
Initializing IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10
IA-32e Mode System Data Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11
IA-32e Mode Interrupts and Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11
64-bit Mode and Compatibility Mode Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11
Switching Out of IA-32e Mode Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12
MODE SWITCHING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12
Switching to Protected Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12
Switching Back to Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-13
INITIALIZATION AND MODE SWITCHING EXAMPLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14
viii Vol. 3A
CONTENTS
PAGE
9.10.1
Assembler Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16
9.10.2
STARTUP.ASM Listing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16
9.10.3
MAIN.ASM Source Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25
9.10.4
Supporting Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25
9.11
MICROCODE UPDATE FACILITIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-27
9.11.1
Microcode Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-28
9.11.2
Optional Extended Signature Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-31
9.11.3
Processor Identification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-32
9.11.4
Platform Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-32
9.11.5
Microcode Update Checksum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-33
9.11.6
Microcode Update Loader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-34
9.11.6.1
Hard Resets in Update Loading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35
9.11.6.2
Update in a Multiprocessor System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35
9.11.6.3
Update in a System Supporting Intel Hyper-Threading Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35
9.11.6.4
Update in a System Supporting Dual-Core Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35
9.11.6.5
Update Loader Enhancements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35
9.11.7
Update Signature and Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-36
9.11.7.1
Determining the Signature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-36
9.11.7.2
Authenticating the Update. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-37
9.11.8
Pentium 4, Intel Xeon, and P6 Family Processor
Microcode Update Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-37
9.11.8.1
Responsibilities of the BIOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-38
9.11.8.2
Responsibilities of the Calling Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-39
9.11.8.3
Microcode Update Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
9.11.8.4
INT 15H-based Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
9.11.8.5
Function 00H—Presence Test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
9.11.8.6
Function 01H—Write Microcode Update Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-43
9.11.8.7
Function 02H—Microcode Update Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-46
9.11.8.8
Function 03H—Read Microcode Update Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-47
9.11.8.9
Return Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-48
CHAPTER 10
ADVANCED PROGRAMMABLE
INTERRUPT CONTROLLER (APIC)
10.1
10.2
10.3
10.4
10.4.1
10.4.2
10.4.3
10.4.4
10.4.5
10.4.6
10.4.7
10.4.7.1
10.4.7.2
10.4.7.3
10.4.7.4
10.4.8
10.5
10.5.1
10.5.2
10.5.3
10.5.4
10.5.4.1
10.5.5
10.6
10.6.1
10.6.2
10.6.2.1
10.6.2.2
10.6.2.3
LOCAL AND I/O APIC OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1
SYSTEM BUS VS. APIC BUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4
THE INTEL® 82489DX EXTERNAL APIC, THE APIC, THE XAPIC, AND THE X2APIC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4
LOCAL APIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4
The Local APIC Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4
Presence of the Local APIC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-7
Enabling or Disabling the Local APIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8
Local APIC Status and Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8
Relocating the Local APIC Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-9
Local APIC ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-9
Local APIC State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10
Local APIC State After Power-Up or Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10
Local APIC State After It Has Been Software Disabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11
Local APIC State After an INIT Reset (“Wait-for-SIPI” State) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11
Local APIC State After It Receives an INIT-Deassert IPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11
Local APIC Version Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11
HANDLING LOCAL INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12
Local Vector Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12
Valid Interrupt Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-14
Error Handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-15
APIC Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-16
TSC-Deadline Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-17
Local Interrupt Acceptance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-18
ISSUING INTERPROCESSOR INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19
Interrupt Command Register (ICR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19
Determining IPI Destination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-23
Physical Destination Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-23
Logical Destination Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-23
Broadcast/Self Delivery Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-25
Vol. 3A ix
CONTENTS
PAGE
10.6.2.4
10.6.3
10.7
10.8
10.8.1
10.8.2
10.8.3
10.8.3.1
10.8.4
10.8.5
10.8.6
10.8.6.1
10.9
10.10
Lowest Priority Delivery Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-25
IPI Delivery and Acceptance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-26
SYSTEM AND APIC BUS ARBITRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-26
HANDLING INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-26
Interrupt Handling with the Pentium 4 and Intel Xeon Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-27
Interrupt Handling with the P6 Family and Pentium Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-27
Interrupt, Task, and Processor Priority . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-28
Task and Processor Priorities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-29
Interrupt Acceptance for Fixed Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-30
Signaling Interrupt Servicing Completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-31
Task Priority in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-31
Interaction of Task Priorities between CR8 and APIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-32
SPURIOUS INTERRUPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-32
APIC BUS MESSAGE PASSING MECHANISM AND
PROTOCOL (P6 FAMILY, PENTIUM PROCESSORS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-33
10.10.1
Bus Message Formats. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-34
10.11 MESSAGE SIGNALLED INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-34
10.11.1
Message Address Register Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-34
10.11.2
Message Data Register Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-35
10.12 EXTENDED XAPIC (X2APIC). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-36
10.12.1
Detecting and Enabling x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-37
10.12.1.1
Instructions to Access APIC Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-37
10.12.1.2
x2APIC Register Address Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-38
10.12.1.3
Reserved Bit Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-40
10.12.2
x2APIC Register Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-40
10.12.3
MSR Access in x2APIC Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-40
10.12.4
VM-Exit Controls for MSRs and x2APIC Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-41
10.12.5
x2APIC State Transitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-41
10.12.5.1
x2APIC States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-41
x2APIC After Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-42
x2APIC Transitions From x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-42
x2APIC Transitions From Disabled Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-43
State Changes From xAPIC Mode to x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-43
10.12.6
Routing of Device Interrupts in x2APIC Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-43
10.12.7
Initialization by System Software. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-43
10.12.8
CPUID Extensions And Topology Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-43
10.12.8.1
Consistency of APIC IDs and CPUID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-44
10.12.9
ICR Operation in x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-44
10.12.10 Determining IPI Destination in x2APIC Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-45
10.12.10.1
Logical Destination Mode in x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-45
10.12.10.2
Deriving Logical x2APIC ID from the Local x2APIC ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-46
10.12.11 SELF IPI Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-47
10.13 APIC BUS MESSAGE FORMATS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-47
10.13.1
Bus Message Formats. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-47
10.13.2
EOI Message. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-47
10.13.2.1
Short Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-48
10.13.2.2
Non-focused Lowest Priority Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-49
10.13.2.3
APIC Bus Status Cycles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-50
CHAPTER 11
MEMORY CACHE CONTROL
11.1
11.2
11.3
11.3.1
11.3.2
11.3.3
11.4
11.5
11.5.1
11.5.2
11.5.2.1
11.5.2.2
x Vol. 3A
INTERNAL CACHES, TLBS, AND BUFFERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1
CACHING TERMINOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5
METHODS OF CACHING AVAILABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-6
Buffering of Write Combining Memory Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-7
Choosing a Memory Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-8
Code Fetches in Uncacheable Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-9
CACHE CONTROL PROTOCOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-9
CACHE CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-10
Cache Control Registers and Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-10
Precedence of Cache Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-13
Selecting Memory Types for Pentium Pro and Pentium II Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-14
Selecting Memory Types for Pentium III and More Recent Processor Families . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-15
CONTENTS
PAGE
11.5.2.3
Writing Values Across Pages with Different Memory Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-16
11.5.3
Preventing Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-16
11.5.4
Disabling and Enabling the L3 Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-17
11.5.5
Cache Management Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-17
11.5.6
L1 Data Cache Context Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-18
11.5.6.1
Adaptive Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-18
11.5.6.2
Shared Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-18
11.6
SELF-MODIFYING CODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-18
11.7
IMPLICIT CACHING (PENTIUM 4, INTEL XEON,
AND P6 FAMILY PROCESSORS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-19
11.8
EXPLICIT CACHING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-19
11.9
INVALIDATING THE TRANSLATION LOOKASIDE BUFFERS (TLBS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-19
11.10 STORE BUFFER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-20
11.11 MEMORY TYPE RANGE REGISTERS (MTRRS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-20
11.11.1
MTRR Feature Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-21
11.11.2
Setting Memory Ranges with MTRRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-22
11.11.2.1
IA32_MTRR_DEF_TYPE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-22
11.11.2.2
Fixed Range MTRRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-23
11.11.2.3
Variable Range MTRRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-23
11.11.2.4
System-Management Range Register Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-25
11.11.3
Example Base and Mask Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-26
11.11.3.1
Base and Mask Calculations for Greater-Than 36-bit Physical Address Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-27
11.11.4
Range Size and Alignment Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-28
11.11.4.1
MTRR Precedences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-28
11.11.5
MTRR Initialization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-29
11.11.6
Remapping Memory Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-29
11.11.7
MTRR Maintenance Programming Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-29
11.11.7.1
MemTypeGet() Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-29
11.11.7.2
MemTypeSet() Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-31
11.11.8
MTRR Considerations in MP Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-32
11.11.9
Large Page Size Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-33
11.12 PAGE ATTRIBUTE TABLE (PAT). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-33
11.12.1
Detecting Support for the PAT Feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-34
11.12.2
IA32_PAT MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-34
11.12.3
Selecting a Memory Type from the PAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-35
11.12.4
Programming the PAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-35
11.12.5
PAT Compatibility with Earlier IA-32 Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-36
CHAPTER 12
INTEL® MMX™ TECHNOLOGY SYSTEM PROGRAMMING
12.1
12.2
12.2.1
12.3
12.4
12.5
12.5.1
12.6
EMULATION OF THE MMX INSTRUCTION SET. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1
THE MMX STATE AND MMX REGISTER ALIASING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1
Effect of MMX, x87 FPU, FXSAVE, and FXRSTOR
Instructions on the x87 FPU Tag Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3
SAVING AND RESTORING THE MMX STATE AND REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3
SAVING MMX STATE ON TASK OR CONTEXT SWITCHES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-4
EXCEPTIONS THAT CAN OCCUR WHEN EXECUTING MMX INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-4
Effect of MMX Instructions on Pending x87 Floating-Point Exceptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5
DEBUGGING MMX CODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5
CHAPTER 13
SYSTEM PROGRAMMING FOR INSTRUCTION SET EXTENSIONS AND PROCESSOR EXTENDED
STATES
13.1
13.1.1
13.1.2
13.1.3
13.1.4
13.1.5
13.1.6
PROVIDING OPERATING SYSTEM SUPPORT FOR
SSE/SSE2/SSE3/SSSE3/SSE4 EXTENSIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1
Adding Support to an Operating System for SSE/SSE2/SSE3/SSSE3/SSE4 Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1
Checking for SSE/SSE2/SSE3/SSSE3/SSE4 Extension Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-2
Checking for Support for the FXSAVE and FXRSTOR Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-2
Initialization of the SSE/SSE2/SSE3/SSSE3/SSE4 Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-2
Providing Non-Numeric Exception Handlers for Exceptions Generated by the SSE/SSE2/SSE3/SSSE3/SSE4 Instructions .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-4
Providing an Handler for the SIMD Floating-Point Exception (#XM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-5
Vol. 3A xi
CONTENTS
PAGE
13.1.6.1
13.2
13.3
13.4
13.5
Numeric Error flag and IGNNE# . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-5
EMULATION OF SSE/SSE2/SSE3/SSSE3/SSE4 EXTENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-5
SAVING AND RESTORING THE SSE/SSE2/SSE3/SSSE3/SSE4 STATE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-5
SAVING THE SSE/SSE2/SSE3/SSSE3/SSE4 STATE ON TASK OR CONTEXT SWITCHES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-6
DESIGNING OS FACILITIES FOR AUTOMATICALLY SAVING X87 FPU, MMX, AND SSE/SSE2/SSE3/SSSE3/SSE4 STATE ON TASK
OR CONTEXT SWITCHES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-6
13.5.1
Using the TS Flag to Control the Saving of the
x87 FPU, MMX, SSE, SSE2, SSE3 SSSE3 and SSE4 State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-7
13.6
XSAVE/XRSTOR AND PROCESSOR EXTENDED STATE MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-8
13.6.1
XSAVE Header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-9
13.7
INTEROPERABILITY OF XSAVE/XRSTOR AND FXSAVE/FXRSTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-10
13.8
DETECTION, ENUMERATION, ENABLING PROCESSOR EXTENDED STATE SUPPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-11
13.8.1
Application Programming Model and Processor Extended States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-12
13.9
INTEL ADVANCED VECTOR EXTENSIONS (INTEL AVX) AND YMM STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-13
13.10 YMM STATE MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-13
13.10.1
Detection of YMM State Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-13
13.10.2
Enabling of YMM State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-13
13.10.3
Enabling of SIMD Floating-Exception Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-14
13.10.4
The Layout of XSAVE Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-14
13.10.5
XSAVE/XRSTOR Interaction with YMM State and MXCSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-15
13.10.6
Processor Extended State Save Optimization and XSAVEOPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-16
13.10.6.1
XSAVEOPT Usage Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-17
CHAPTER 14
POWER AND THERMAL MANAGEMENT
ENHANCED INTEL SPEEDSTEP® TECHNOLOGY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-1
Software Interface For Initiating Performance State Transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-1
P-STATE HARDWARE COORDINATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-1
SYSTEM SOFTWARE CONSIDERATIONS AND OPPORTUNISTIC PROCESSOR PERFORMANCE OPERATION . . . . . . . . . . . . . . 14-3
Intel Dynamic Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-3
System Software Interfaces for Opportunistic Processor Performance Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-3
Discover Hardware Support and Enabling of Opportunistic Processor Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4
OS Control of Opportunistic Processor Performance Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4
Required Changes to OS Power Management P-state Policy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4
Application Awareness of Opportunistic Processor Operation (Optional) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-5
Intel Turbo Boost Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-6
Performance and Energy Bias Hint support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-6
MWAIT EXTENSIONS FOR ADVANCED POWER MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-7
THERMAL MONITORING AND PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-7
Catastrophic Shutdown Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-8
Thermal Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-8
Thermal Monitor 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-8
Thermal Monitor 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-9
Two Methods for Enabling TM2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-9
Performance State Transitions and Thermal Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-10
Thermal Status Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-10
Adaptive Thermal Monitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-11
Software Controlled Clock Modulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-11
Extension of Software Controlled Clock Modulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-13
Detection of Thermal Monitor and Software Controlled
Clock Modulation Facilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-13
14.5.4.1
Detection of Software Controlled Clock Modulation Extension. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-13
14.5.5
On Die Digital Thermal Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-13
14.5.5.1
Digital Thermal Sensor Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-13
14.5.5.2
Reading the Digital Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-13
14.5.6
Power Limit Notification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-16
14.6
PACKAGE LEVEL THERMAL MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-16
14.6.1
Support for Passive and Active cooling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-19
14.7
PLATFORM SPECIFIC POWER MANAGEMENT SUPPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-19
14.7.1
RAPL Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-20
14.7.2
RAPL Domains and Platform Specificity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-20
14.7.3
Package RAPL Domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-21
14.7.4
PP0/PP1 RAPL Domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-23
14.7.5
DRAM RAPL Domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-25
14.1
14.1.1
14.2
14.3
14.3.1
14.3.2
14.3.2.1
14.3.2.2
14.3.2.3
14.3.2.4
14.3.3
14.3.4
14.4
14.5
14.5.1
14.5.2
14.5.2.1
14.5.2.2
14.5.2.3
14.5.2.4
14.5.2.5
14.5.2.6
14.5.3
14.5.3.1
14.5.4
xii Vol. 3A
CONTENTS
PAGE
CHAPTER 15
MACHINE-CHECK ARCHITECTURE
15.1
MACHINE-CHECK ARCHITECTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1
15.2
COMPATIBILITY WITH PENTIUM PROCESSOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1
15.3
MACHINE-CHECK MSRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-2
15.3.1
Machine-Check Global Control MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-2
15.3.1.1
IA32_MCG_CAP MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-2
15.3.1.2
IA32_MCG_STATUS MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
15.3.1.3
IA32_MCG_CTL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-4
15.3.2
Error-Reporting Register Banks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-4
15.3.2.1
IA32_MCi_CTL MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-4
15.3.2.2
IA32_MCi_STATUS MSRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-4
15.3.2.3
IA32_MCi_ADDR MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-7
15.3.2.4
IA32_MCi_MISC MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-7
15.3.2.5
IA32_MCi_CTL2 MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-8
15.3.2.6
IA32_MCG Extended Machine Check State MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-9
15.3.3
Mapping of the Pentium Processor Machine-Check Errors
to the Machine-Check Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-11
15.4
ENHANCED CACHE ERROR REPORTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-11
15.5
CORRECTED MACHINE CHECK ERROR INTERRUPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-11
15.5.1
CMCI Local APIC Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-12
15.5.2
System Software Recommendation for Managing CMCI and Machine Check Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-12
15.5.2.1
CMCI Initialization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-12
15.5.2.2
CMCI Threshold Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-13
15.5.2.3
CMCI Interrupt Handler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-13
15.6
RECOVERY OF UNCORRECTED RECOVERABLE (UCR) ERRORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-14
15.6.1
Detection of Software Error Recovery Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-14
15.6.2
UCR Error Reporting and Logging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-14
15.6.3
UCR Error Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-15
15.6.4
UCR Error Overwrite Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-16
15.7
MACHINE-CHECK AVAILABILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-17
15.8
MACHINE-CHECK INITIALIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-17
15.9
INTERPRETING THE MCA ERROR CODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-18
15.9.1
Simple Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-18
15.9.2
Compound Error Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-19
15.9.2.1
Correction Report Filtering (F) Bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-19
15.9.2.2
Transaction Type (TT) Sub-Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-19
15.9.2.3
Level (LL) Sub-Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-20
15.9.2.4
Request (RRRR) Sub-Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-20
15.9.2.5
Bus and Interconnect Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-20
15.9.2.6
Memory Controller Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-21
15.9.3
Architecturally Defined UCR Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-21
15.9.3.1
Architecturally Defined SRAO Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-21
15.9.3.2
Architecturally Defined SRAR Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-22
15.9.4
Multiple MCA Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-24
15.9.5
Machine-Check Error Codes Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-24
15.10 GUIDELINES FOR WRITING MACHINE-CHECK SOFTWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-24
15.10.1
Machine-Check Exception Handler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-25
15.10.2
Pentium Processor Machine-Check Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-26
15.10.3
Logging Correctable Machine-Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-26
15.10.4
Machine-Check Software Handler Guidelines for Error Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-28
15.10.4.1
Machine-Check Exception Handler for Error Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-28
15.10.4.2
Corrected Machine-Check Handler for Error Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-32
CHAPTER 16
INTERPRETING MACHINE-CHECK
ERROR CODES
16.1
16.2
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY 06H MACHINE ERROR CODES FOR MACHINE CHECK . . . . 16-1
INCREMENTAL DECODING INFORMATION: INTEL CORE 2 PROCESSOR FAMILY MACHINE ERROR CODES FOR MACHINE CHECK
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-3
16.2.1
Model-Specific Machine Check Error Codes for Intel Xeon Processor 7400 Series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-5
16.2.1.1
Processor Machine Check Status Register
Incremental MCA Error Code Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-6
Vol. 3A xiii
CONTENTS
PAGE
16.2.2
16.2.2.1
16.2.2.2
16.3
16.3.1
16.3.2
16.3.3
16.4
16.4.1
16.4.2
16.4.3
16.5
16.5.1
16.5.2
16.6
16.6.1
16.6.1.1
16.6.2
16.6.3
16.6.3.1
16.6.3.2
16.6.3.3
Intel Xeon Processor 7400 Model Specific Error Code Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-6
Processor Model Specific Error Code Field
Type B: Bus and Interconnect Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-6
Processor Model Specific Error Code Field
Type C: Cache Bus Controller Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-7
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE
06_1AH, MACHINE ERROR CODES FOR MACHINE CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-7
Intel QPI Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8
Internal Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8
Memory Controller Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-9
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE
06_2DH, MACHINE ERROR CODES FOR MACHINE CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-10
Internal Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-10
Intel QPI Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-11
Integrated Memory Controller Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-11
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE
06_3EH, MACHINE ERROR CODES FOR MACHINE CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-13
Internal Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-13
Integrated Memory Controller Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-14
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY 0FH MACHINE ERROR CODES FOR MACHINE CHECK . . 16-16
Model-Specific Machine Check Error Codes for Intel Xeon Processor MP 7100 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-17
Processor Machine Check Status Register
MCA Error Code Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-17
Other_Info Field (all MCA Error Types) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-18
Processor Model Specific Error Code Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-19
MCA Error Type A: L3 Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-19
Processor Model Specific Error Code Field Type B: Bus and Interconnect Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-19
Processor Model Specific Error Code Field Type C: Cache Bus Controller Error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-20
CHAPTER 17
DEBUGGING, BRANCH PROFILING, AND TIME-STAMP COUNTER
17.1
17.2
17.2.1
17.2.2
17.2.3
17.2.4
17.2.5
17.2.6
17.3
17.3.1
17.3.1.1
17.3.1.2
17.3.1.3
17.3.1.4
17.3.1.5
17.3.2
17.4
17.4.1
17.4.2
17.4.3
17.4.4
17.4.4.1
17.4.5
17.4.6
17.4.7
17.4.8
17.4.8.1
17.4.8.2
17.4.8.3
17.4.9
17.4.9.1
17.4.9.2
17.4.9.3
OVERVIEW OF DEBUG SUPPORT FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-1
DEBUG REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-2
Debug Address Registers (DR0-DR3). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-3
Debug Registers DR4 and DR5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-3
Debug Status Register (DR6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-3
Debug Control Register (DR7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-3
Breakpoint Field Recognition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-5
Debug Registers and Intel® 64 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-6
DEBUG EXCEPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-7
Debug Exception (#DB)—Interrupt Vector 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-7
Instruction-Breakpoint Exception Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-7
Data Memory and I/O Breakpoint Exception Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-8
General-Detect Exception Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-9
Single-Step Exception Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-9
Task-Switch Exception Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-9
Breakpoint Exception (#BP)—Interrupt Vector 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-9
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-9
IA32_DEBUGCTL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-10
Monitoring Branches, Exceptions, and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-11
Single-Stepping on Branches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-12
Branch Trace Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-12
Branch Trace Message Visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-12
Branch Trace Store (BTS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-12
CPL-Qualified Branch Trace Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-13
Freezing LBR and Performance Counters on PMI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-13
LBR Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-13
LBR Stack and Intel® 64 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-14
LBR Stack and IA-32 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-15
Last Exception Records and Intel 64 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-15
BTS and DS Save Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-15
DS Save Area and IA-32e Mode Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-17
Setting Up the DS Save Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-19
Setting Up the BTS Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-20
xiv Vol. 3A
CONTENTS
PAGE
17.4.9.4
Setting Up CPL-Qualified BTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-21
17.4.9.5
Writing the DS Interrupt Service Routine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-21
17.5
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (INTEL® CORE™2 DUO AND INTEL® ATOM™ PROCESSOR FAMILY)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-22
17.5.1
LBR Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-22
17.6
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING FOR PROCESSORS BASED ON INTEL® MICROARCHITECTURE CODE
NAME NEHALEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-23
17.6.1
LBR Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-24
17.6.2
Filtering of Last Branch Records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-25
17.7
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING FOR PROCESSORS BASED ON INTEL® MICROARCHITECTURE CODE
NAME SANDY BRIDGE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-25
17.8
LAST BRANCH, CALL STACK, INTERRUPT, AND EXCEPTION RECORDING FOR PROCESSORS BASED ON INTEL®
MICROARCHITECTURE CODE NAME HASWELL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-26
17.8.1
LBR Stack Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-27
17.9
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (PROCESSORS BASED ON INTEL NETBURST® MICROARCHITECTURE)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-27
17.9.1
MSR_DEBUGCTLA MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-28
17.9.2
LBR Stack for Processors Based on Intel NetBurst® Microarchitecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-29
17.9.3
Last Exception Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-30
17.10 LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (INTEL® CORE™ SOLO AND INTEL® CORE™ DUO PROCESSORS)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-30
17.11 LAST BRANCH, INTERRUPT, AND EXCEPTION
RECORDING (PENTIUM M PROCESSORS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-32
17.12 LAST BRANCH, INTERRUPT, AND EXCEPTION
RECORDING (P6 FAMILY PROCESSORS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-33
17.12.1
DEBUGCTLMSR Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-33
17.12.2
Last Branch and Last Exception MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-34
17.12.3
Monitoring Branches, Exceptions, and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-34
17.13 TIME-STAMP COUNTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-35
17.13.1
Invariant TSC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-36
17.13.2
IA32_TSC_AUX Register and RDTSCP Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-36
17.13.3
Time-Stamp Counter Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-36
17.14 CACHE QUALITY-OF-SERVICE (QOS) MONITORING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-37
17.14.1
Overview of Cache QoS Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-37
17.14.2
Enumeration and Detection Support of Cache QoS Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-37
CHAPTER 18
PERFORMANCE MONITORING
18.1
18.2
18.2.1
18.2.1.1
18.2.2
18.2.2.1
18.2.2.2
18.2.2.3
18.2.3
18.3
18.4
18.4.1
18.4.2
18.4.3
18.4.4
18.4.4.1
18.4.4.2
18.4.4.3
18.4.4.4
18.5
18.6
18.6.1
18.6.1.1
18.6.1.2
18.6.1.3
18.6.2
PERFORMANCE MONITORING OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-1
ARCHITECTURAL PERFORMANCE MONITORING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-2
Architectural Performance Monitoring Version 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-2
Architectural Performance Monitoring Version 1 Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-3
Additional Architectural Performance Monitoring Extensions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-4
Architectural Performance Monitoring Version 2 Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-5
Architectural Performance Monitoring Version 3 Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-7
Full-Width Writes to Performance Counter Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-9
Pre-defined Architectural Performance Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-9
PERFORMANCE MONITORING (INTEL® CORE™ SOLO AND INTEL® CORE™ DUO PROCESSORS) . . . . . . . . . . . . . . . . . . . . . . . . . 18-11
PERFORMANCE MONITORING (PROCESSORS BASED ON INTEL® CORE™ MICROARCHITECTURE) . . . . . . . . . . . . . . . . . . . 18-12
Fixed-function Performance Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-13
Global Counter Control Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-14
At-Retirement Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-16
Precise Event Based Sampling (PEBS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-16
Setting up the PEBS Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-17
PEBS Record Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-17
Writing a PEBS Interrupt Service Routine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-17
Re-configuring PEBS Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-18
PERFORMANCE MONITORING (PROCESSORS BASED ON INTEL® ATOM™ MICROARCHITECTURE). . . . . . . . . . . . . . . . . . . 18-19
PERFORMANCE MONITORING FOR PROCESSORS BASED ON INTEL® MICROARCHITECTURE CODE NAME NEHALEM. . 18-19
Enhancements of Performance Monitoring in the Processor Core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-20
Precise Event Based Sampling (PEBS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-20
Load Latency Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-24
Off-core Response Performance Monitoring in the Processor Core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-26
Performance Monitoring Facility in the Uncore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-28
Vol. 3A xv
CONTENTS
PAGE
18.6.2.1
Uncore Performance Monitoring Management Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-29
18.6.2.2
Uncore Performance Event Configuration Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-31
18.6.2.3
Uncore Address/Opcode Match MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-32
18.6.3
Intel® Xeon® Processor 7500 Series Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-33
18.7
PERFORMANCE MONITORING FOR PROCESSORS BASED ON INTEL® MICROARCHITECTURE CODE NAME WESTMERE 18-35
18.7.1
Intel® Xeon® Processor E7 Family Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-35
18.8
PERFORMANCE MONITORING FOR PROCESSORS BASED ON INTEL® MICROARCHITECTURE CODE NAME SANDY BRIDGE . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-36
18.8.1
Global Counter Control Facilities In Intel® Microarchitecture Code Name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . .18-37
18.8.2
Counter Coalescence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-38
18.8.3
Full Width Writes to Performance Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-38
18.8.4
PEBS Support in Intel® Microarchitecture Code Name Sandy Bridge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-39
18.8.4.1
PEBS Record Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-40
18.8.4.2
Load Latency Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-41
18.8.4.3
Precise Store Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-42
18.8.4.4
Precise Distribution of Instructions Retired (PDIR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-43
18.8.5
Off-core Response Performance Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-43
18.8.6
Uncore Performance Monitoring Facilities In Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx
Processor Series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-46
18.8.6.1
Uncore Performance Monitoring Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-48
18.8.7
Intel® Xeon® Processor E5 Family Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-48
18.8.8
Intel® Xeon® Processor E5 Family Uncore Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-49
18.9
3RD GENERATION INTEL® CORE™ PROCESSOR PERFORMANCE MONITORING FACILITY. . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-49
18.10 NEXT GENERATION INTEL® CORE™ PROCESSOR PERFORMANCE MONITORING FACILITY . . . . . . . . . . . . . . . . . . . . . . . . . . 18-49
18.10.1
Precise Event Based Sampling (PEBS) Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-50
18.10.2
PEBS Data Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-51
18.10.3
PEBS Data Address Profiling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-51
18.10.3.1
EventingIP Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-52
18.10.4
Off-core Response Performance Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-53
18.10.5
Performance Monitoring and Intel® TSX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-53
18.10.5.1
Intel TSX and PEBS Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-54
18.10.6
Uncore Performance Monitoring Facilities in Next Generation Intel® Core™ Processors. . . . . . . . . . . . . . . . . . . . . . . . . .18-55
18.11 PERFORMANCE MONITORING (PROCESSORS
BASED ON INTEL NETBURST® MICROARCHITECTURE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-56
18.11.1
ESCR MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-59
18.11.2
Performance Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-60
18.11.3
CCCR MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-61
18.11.4
Debug Store (DS) Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-63
18.11.5
Programming the Performance Counters
for Non-Retirement Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-63
18.11.5.1
Selecting Events to Count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-63
18.11.5.2
Filtering Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-65
18.11.5.3
Starting Event Counting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-66
18.11.5.4
Reading a Performance Counter’s Count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-66
18.11.5.5
Halting Event Counting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-66
18.11.5.6
Cascading Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-67
18.11.5.7
EXTENDED CASCADING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-67
18.11.5.8
Generating an Interrupt on Overflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-68
18.11.5.9
Counter Usage Guideline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-69
18.11.6
At-Retirement Counting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-69
18.11.6.1
Using At-Retirement Counting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-70
18.11.6.2
Tagging Mechanism for Front_end_event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-70
18.11.6.3
Tagging Mechanism For Execution_event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-70
18.11.6.4
Tagging Mechanism for Replay_event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-71
18.11.7
Precise Event-Based Sampling (PEBS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-71
18.11.7.1
Detection of the Availability of the PEBS Facilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-72
18.11.7.2
Setting Up the DS Save Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-72
18.11.7.3
Setting Up the PEBS Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-72
18.11.7.4
Writing a PEBS Interrupt Service Routine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-72
18.11.7.5
Other DS Mechanism Implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-72
18.11.8
Operating System Implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-72
18.12 PERFORMANCE MONITORING AND INTEL HYPER-THREADING TECHNOLOGY IN PROCESSORS BASED ON INTEL NETBURST®
MICROARCHITECTURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-73
18.12.1
ESCR MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-73
18.12.2
CCCR MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-74
xvi Vol. 3A
CONTENTS
PAGE
18.12.3
IA32_PEBS_ENABLE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-75
18.12.4
Performance Monitoring Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-76
18.13 COUNTING CLOCKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-77
18.13.1
Non-Halted Clockticks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-78
18.13.2
Non-Sleep Clockticks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-78
18.13.3
Incrementing the Time-Stamp Counter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-79
18.13.4
Non-Halted Reference Clockticks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-79
18.13.5
Cycle Counting and Opportunistic Processor Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-79
18.14 PERFORMANCE MONITORING, BRANCH PROFILING AND SYSTEM EVENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-79
18.15 PERFORMANCE MONITORING AND DUAL-CORE TECHNOLOGY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-80
18.16 PERFORMANCE MONITORING ON 64-BIT INTEL XEON PROCESSOR MP WITH UP TO 8-MBYTE L3 CACHE . . . . . . . . . . . . 18-80
18.17 PERFORMANCE MONITORING ON L3 AND CACHING BUS CONTROLLER SUB-SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-83
18.17.1
Overview of Performance Monitoring with L3/Caching Bus Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-85
18.17.2
GBSQ Event Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-86
18.17.3
GSNPQ Event Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-87
18.17.4
FSB Event Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-88
18.17.4.1
FSB Sub-Event Mask Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-88
18.17.5
Common Event Control Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-89
18.18 PERFORMANCE MONITORING (P6 FAMILY PROCESSOR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-89
18.18.1
PerfEvtSel0 and PerfEvtSel1 MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-90
18.18.2
PerfCtr0 and PerfCtr1 MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-91
18.18.3
Starting and Stopping the Performance-Monitoring Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-91
18.18.4
Event and Time-Stamp Monitoring Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-91
18.18.5
Monitoring Counter Overflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-92
18.19 PERFORMANCE MONITORING (PENTIUM PROCESSORS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-92
18.19.1
Control and Event Select Register (CESR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-93
18.19.2
Use of the Performance-Monitoring Pins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-93
18.19.3
Events Counted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-94
CHAPTER 19
PERFORMANCE-MONITORING EVENTS
19.1
19.2
19.3
19.4
19.5
19.6
19.7
19.8
19.9
19.10
19.11
19.12
19.13
19.14
ARCHITECTURAL PERFORMANCE-MONITORING EVENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1
PERFORMANCE MONITORING EVENTS FOR NEXT GENERATION INTEL® CORE™ PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . 19-2
PERFORMANCE MONITORING EVENTS FOR 3RD GENERATION INTEL® CORE™ PROCESSORS . . . . . . . . . . . . . . . . . . . . . . 19-13
PERFORMANCE MONITORING EVENTS FOR 2ND GENERATION INTEL® CORE™ I7-2XXX, INTEL® CORE™ I5-2XXX,
INTEL® CORE™ I3-2XXX PROCESSOR SERIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-22
PERFORMANCE MONITORING EVENTS FOR INTEL® CORE™ I7 PROCESSOR FAMILY AND INTEL® XEON® PROCESSOR
FAMILY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-36
PERFORMANCE MONITORING EVENTS FOR PROCESSORS BASED ON INTEL® MICROARCHITECTURE CODE NAME WESTMERE
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-65
PERFORMANCE MONITORING EVENTS FOR INTEL® XEON® PROCESSOR 5200, 5400 SERIES AND INTEL® CORE™2 EXTREME
PROCESSORS QX 9000 SERIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-97
PERFORMANCE MONITORING EVENTS FOR INTEL® XEON® PROCESSOR 3000, 3200, 5100, 5300 SERIES AND
INTEL® CORE™2 DUO PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-97
PERFORMANCE MONITORING EVENTS FOR INTEL® ATOM™ PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-123
PERFORMANCE MONITORING EVENTS FOR INTEL® CORE™ SOLO AND INTEL® CORE™ DUO PROCESSORS . . . . . . . 19-137
PENTIUM® 4 AND INTEL® XEON® PROCESSOR PERFORMANCE-MONITORING EVENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-142
PERFORMANCE MONITORING EVENTS FOR INTEL® PENTIUM® M PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-171
P6 FAMILY PROCESSOR PERFORMANCE-MONITORING EVENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-173
PENTIUM PROCESSOR PERFORMANCE-MONITORING EVENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-182
CHAPTER 20
8086 EMULATION
20.1
20.1.1
20.1.2
20.1.3
20.1.4
20.2
20.2.1
20.2.2
20.2.3
REAL-ADDRESS MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-1
Address Translation in Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-2
Registers Supported in Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-3
Instructions Supported in Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-3
Interrupt and Exception Handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-4
VIRTUAL-8086 MODE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-5
Enabling Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-6
Structure of a Virtual-8086 Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-7
Paging of Virtual-8086 Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-7
Vol. 3A xvii
CONTENTS
PAGE
20.2.4
Protection within a Virtual-8086 Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-8
20.2.5
Entering Virtual-8086 Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-8
20.2.6
Leaving Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-9
20.2.7
Sensitive Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-10
20.2.8
Virtual-8086 Mode I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-10
20.2.8.1
I/O-Port-Mapped I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-11
20.2.8.2
Memory-Mapped I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-11
20.2.8.3
Special I/O Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-11
20.3
INTERRUPT AND EXCEPTION HANDLING IN VIRTUAL-8086 MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-11
20.3.1
Class 1—Hardware Interrupt and Exception Handling in Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-12
20.3.1.1
Handling an Interrupt or Exception Through a Protected-Mode Trap or Interrupt Gate . . . . . . . . . . . . . . . . . . . . . . . . .20-12
20.3.1.2
Handling an Interrupt or Exception With an 8086 Program Interrupt or Exception Handler. . . . . . . . . . . . . . . . . . . . .20-14
20.3.1.3
Handling an Interrupt or Exception Through a Task Gate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-14
20.3.2
Class 2—Maskable Hardware Interrupt Handling in Virtual-8086 Mode Using the Virtual Interrupt Mechanism . . . . .20-15
20.3.3
Class 3—Software Interrupt Handling in Virtual-8086 Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-16
20.3.3.1
Method 1: Software Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-18
20.3.3.2
Methods 2 and 3: Software Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-18
20.3.3.3
Method 4: Software Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-19
20.3.3.4
Method 5: Software Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-19
20.3.3.5
Method 6: Software Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-19
20.4
PROTECTED-MODE VIRTUAL INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-20
CHAPTER 21
MIXING 16-BIT AND 32-BIT CODE
21.1
21.2
21.3
21.4
21.4.1
21.4.2
21.4.2.1
21.4.2.2
21.4.3
21.4.4
21.4.5
DEFINING 16-BIT AND 32-BIT PROGRAM MODULES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-1
MIXING 16-BIT AND 32-BIT OPERATIONS WITHIN A CODE SEGMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-2
SHARING DATA AMONG MIXED-SIZE CODE SEGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-3
TRANSFERRING CONTROL AMONG MIXED-SIZE CODE SEGMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-3
Code-Segment Pointer Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-4
Stack Management for Control Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-4
Controlling the Operand-Size Attribute For a Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-5
Passing Parameters With a Gate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-6
Interrupt Control Transfers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-6
Parameter Translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-6
Writing Interface Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-6
CHAPTER 22
ARCHITECTURE COMPATIBILITY
22.1
22.2
22.3
22.4
22.5
22.6
22.7
22.8
22.9
22.10
22.11
22.12
22.13
22.13.1
22.14
22.15
22.16
22.16.1
22.17
22.17.1
22.17.2
22.18
22.18.1
22.18.2
PROCESSOR FAMILIES AND CATEGORIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-1
RESERVED BITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-1
ENABLING NEW FUNCTIONS AND MODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2
DETECTING THE PRESENCE OF NEW FEATURES THROUGH SOFTWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2
INTEL MMX TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2
STREAMING SIMD EXTENSIONS (SSE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3
STREAMING SIMD EXTENSIONS 2 (SSE2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3
STREAMING SIMD EXTENSIONS 3 (SSE3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3
ADDITIONAL STREAMING SIMD EXTENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3
INTEL HYPER-THREADING TECHNOLOGY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3
MULTI-CORE TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4
SPECIFIC FEATURES OF DUAL-CORE PROCESSOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4
NEW INSTRUCTIONS IN THE PENTIUM AND LATER IA-32 PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4
Instructions Added Prior to the Pentium Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4
OBSOLETE INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-5
UNDEFINED OPCODES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-5
NEW FLAGS IN THE EFLAGS REGISTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-5
Using EFLAGS Flags to Distinguish Between 32-Bit IA-32 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-6
STACK OPERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-6
PUSH SP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-6
EFLAGS Pushed on the Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-6
X87 FPU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-6
Control Register CR0 Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-7
x87 FPU Status Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-7
xviii Vol. 3A
CONTENTS
PAGE
22.18.2.1
Condition Code Flags (C0 through C3). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-7
22.18.2.2
Stack Fault Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-8
22.18.3
x87 FPU Control Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-8
22.18.4
x87 FPU Tag Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-8
22.18.5
Data Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-8
22.18.5.1
NaNs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-8
22.18.5.2
Pseudo-zero, Pseudo-NaN, Pseudo-infinity, and Unnormal Formats. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-9
22.18.6
Floating-Point Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-9
22.18.6.1
Denormal Operand Exception (#D). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-9
22.18.6.2
Numeric Overflow Exception (#O) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-9
22.18.6.3
Numeric Underflow Exception (#U) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-10
22.18.6.4
Exception Precedence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-10
22.18.6.5
CS and EIP For FPU Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-10
22.18.6.6
FPU Error Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-10
22.18.6.7
Assertion of the FERR# Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-10
22.18.6.8
Invalid Operation Exception On Denormals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-11
22.18.6.9
Alignment Check Exceptions (#AC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-11
22.18.6.10
Segment Not Present Exception During FLDENV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-11
22.18.6.11
Device Not Available Exception (#NM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-11
22.18.6.12
Coprocessor Segment Overrun Exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-11
22.18.6.13
General Protection Exception (#GP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-11
22.18.6.14
Floating-Point Error Exception (#MF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-11
22.18.7
Changes to Floating-Point Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-12
22.18.7.1
FDIV, FPREM, and FSQRT Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-12
22.18.7.2
FSCALE Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-12
22.18.7.3
FPREM1 Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-12
22.18.7.4
FPREM Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-12
22.18.7.5
FUCOM, FUCOMP, and FUCOMPP Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-12
22.18.7.6
FPTAN Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-12
22.18.7.7
Stack Overflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-12
22.18.7.8
FSIN, FCOS, and FSINCOS Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-13
22.18.7.9
FPATAN Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-13
22.18.7.10
F2XM1 Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-13
22.18.7.11
FLD Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-13
22.18.7.12
FXTRACT Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-13
22.18.7.13
Load Constant Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-13
22.18.7.14
FSETPM Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-14
22.18.7.15
FXAM Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-14
22.18.7.16
FSAVE and FSTENV Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-14
22.18.8
Transcendental Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-14
22.18.9
Obsolete Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-14
22.18.10 WAIT/FWAIT Prefix Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-14
22.18.11 Operands Split Across Segments and/or Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-14
22.18.12 FPU Instruction Synchronization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-15
22.19 SERIALIZING INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-15
22.20 FPU AND MATH COPROCESSOR INITIALIZATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-15
22.20.1
Intel® 387 and Intel® 287 Math Coprocessor Initialization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-15
22.20.2
Intel486 SX Processor and Intel 487 SX Math Coprocessor Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-15
22.21 CONTROL REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-16
22.22 MEMORY MANAGEMENT FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-18
22.22.1
New Memory Management Control Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-18
22.22.1.1
Physical Memory Addressing Extension. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-18
22.22.1.2
Global Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-18
22.22.1.3
Larger Page Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-18
22.22.2
CD and NW Cache Control Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-18
22.22.3
Descriptor Types and Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-18
22.22.4
Changes in Segment Descriptor Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.23 DEBUG FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.23.1
Differences in Debug Register DR6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.23.2
Differences in Debug Register DR7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.23.3
Debug Registers DR4 and DR5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.24 RECOGNITION OF BREAKPOINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.25 EXCEPTIONS AND/OR EXCEPTION CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-20
22.25.1
Machine-Check Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-21
22.25.2
Priority of Exceptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-21
Vol. 3A xix
CONTENTS
PAGE
22.25.3
22.26
22.26.1
22.26.2
22.26.3
22.27
22.27.1
22.27.2
22.27.3
22.28
22.28.1
22.28.2
22.28.3
22.28.4
22.28.5
22.29
22.29.1
22.29.2
22.30
22.30.1
22.30.2
22.30.3
22.31
22.31.1
22.31.2
22.31.3
22.31.4
22.32
22.33
22.33.1
22.34
22.35
22.36
22.37
22.37.1
22.37.2
22.37.3
22.37.4
22.37.5
22.38
Exception Conditions of Legacy SIMD Instructions Operating on MMX Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-21
INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-26
Interrupt Propagation Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-26
NMI Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-26
IDT Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-26
ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-26
Software Visible Differences Between the Local APIC and the 82489DX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-27
New Features Incorporated in the Local APIC for the P6 Family and Pentium Processors . . . . . . . . . . . . . . . . . . . . . . . . .22-27
New Features Incorporated in the Local APIC of the Pentium 4 and Intel Xeon Processors . . . . . . . . . . . . . . . . . . . . . . . .22-27
TASK SWITCHING AND TSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-27
P6 Family and Pentium Processor TSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-28
TSS Selector Writes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-28
Order of Reads/Writes to the TSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-28
Using A 16-Bit TSS with 32-Bit Constructs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-28
Differences in I/O Map Base Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-28
CACHE MANAGEMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-29
Self-Modifying Code with Cache Enabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-29
Disabling the L3 Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-30
PAGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-30
Large Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-30
PCD and PWT Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-30
Enabling and Disabling Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-31
STACK OPERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-31
Selector Pushes and Pops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-31
Error Code Pushes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-31
Fault Handling Effects on the Stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-32
Interlevel RET/IRET From a 16-Bit Interrupt or Call Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-32
MIXING 16- AND 32-BIT SEGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-32
SEGMENT AND ADDRESS WRAPAROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-32
Segment Wraparound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-33
STORE BUFFERS AND MEMORY ORDERING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-33
BUS LOCKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-34
BUS HOLD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-34
MODEL-SPECIFIC EXTENSIONS TO THE IA-32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-34
Model-Specific Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-35
RDMSR and WRMSR Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-35
Memory Type Range Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-35
Machine-Check Exception and Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-35
Performance-Monitoring Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-36
TWO WAYS TO RUN INTEL 286 PROCESSOR TASKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-36
CHAPTER 23
INTRODUCTION TO VIRTUAL-MACHINE EXTENSIONS
23.1
23.2
23.3
23.4
23.5
23.6
23.7
23.8
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VIRTUAL MACHINE ARCHITECTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
INTRODUCTION TO VMX OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LIFE CYCLE OF VMM SOFTWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VIRTUAL-MACHINE CONTROL STRUCTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DISCOVERING SUPPORT FOR VMX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ENABLING AND ENTERING VMX OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RESTRICTIONS ON VMX OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CHAPTER 24
VIRTUAL-MACHINE CONTROL STRUCTURES
24.1
24.2
24.3
24.4
24.4.1
24.4.2
24.5
24.6
23-1
23-1
23-1
23-2
23-2
23-2
23-3
23-3
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-1
FORMAT OF THE VMCS REGION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-2
ORGANIZATION OF VMCS DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-3
GUEST-STATE AREA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-4
Guest Register State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-4
Guest Non-Register State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-5
HOST-STATE AREA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-7
VM-EXECUTION CONTROL FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-8
xx Vol. 3A
CONTENTS
PAGE
24.6.1
24.6.2
24.6.3
24.6.4
24.6.5
24.6.6
24.6.7
24.6.8
24.6.9
24.6.10
24.6.11
24.6.12
24.6.13
24.6.14
24.6.15
24.6.16
24.7
24.7.1
24.7.2
24.8
24.8.1
24.8.2
24.8.3
24.9
24.9.1
24.9.2
24.9.3
24.9.4
24.9.5
24.10
24.11
24.11.1
24.11.2
24.11.3
24.11.4
24.11.5
Pin-Based VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-8
Processor-Based VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-9
Exception Bitmap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-11
I/O-Bitmap Addresses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-11
Time-Stamp Counter Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-11
Guest/Host Masks and Read Shadows for CR0 and CR4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-11
CR3-Target Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-12
Controls for APIC Virtualization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-12
MSR-Bitmap Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-13
Executive-VMCS Pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-13
Extended-Page-Table Pointer (EPTP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-14
Virtual-Processor Identifier (VPID) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-14
Controls for PAUSE-Loop Exiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-14
VM-Function Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-14
VMCS Shadowing Bitmap Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-15
Controls for Virtualization Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-15
VM-EXIT CONTROL FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-15
VM-Exit Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-15
VM-Exit Controls for MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-16
VM-ENTRY CONTROL FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-17
VM-Entry Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-17
VM-Entry Controls for MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-18
VM-Entry Controls for Event Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-18
VM-EXIT INFORMATION FIELDS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-19
Basic VM-Exit Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-19
Information for VM Exits Due to Vectored Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-20
Information for VM Exits That Occur During Event Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-21
Information for VM Exits Due to Instruction Execution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-21
VM-Instruction Error Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-22
VMCS TYPES: ORDINARY AND SHADOW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-22
SOFTWARE USE OF THE VMCS AND RELATED STRUCTURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-22
Software Use of Virtual-Machine Control Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-22
VMREAD, VMWRITE, and Encodings of VMCS Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-23
Initializing a VMCS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-25
Software Access to Related Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-25
VMXON Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-26
CHAPTER 25
VMX NON-ROOT OPERATION
25.1
25.1.1
25.1.2
25.1.3
25.2
25.3
25.4
25.4.1
25.4.2
25.5
25.5.1
25.5.2
25.5.3
25.5.4
25.5.5
25.5.5.1
25.5.5.2
25.5.5.3
25.5.6
25.5.6.1
25.5.6.2
25.5.6.3
25.6
INSTRUCTIONS THAT CAUSE VM EXITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-1
Relative Priority of Faults and VM Exits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-1
Instructions That Cause VM Exits Unconditionally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-2
Instructions That Cause VM Exits Conditionally. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-2
OTHER CAUSES OF VM EXITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-5
CHANGES TO INSTRUCTION BEHAVIOR IN VMX NON-ROOT OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-6
OTHER CHANGES IN VMX NON-ROOT OPERATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-9
Event Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-9
Treatment of Task Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-10
FEATURES SPECIFIC TO VMX NON-ROOT OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-11
VMX-Preemption Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-11
Monitor Trap Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-11
Translation of Guest-Physical Addresses Using EPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-12
APIC Virtualization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-12
VM Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-12
Enabling VM Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-12
General Operation of the VMFUNC Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-13
EPTP Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-13
Virtualization Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-14
Convertible EPT Violations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-15
Virtualization-Exception Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-15
Delivery of Virtualization Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-16
UNRESTRICTED GUESTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-16
Vol. 3A xxi
CONTENTS
PAGE
CHAPTER 26
VM ENTRIES
26.1
26.2
26.2.1
26.2.1.1
26.2.1.2
26.2.1.3
26.2.2
26.2.3
26.2.4
26.3
26.3.1
26.3.1.1
26.3.1.2
26.3.1.3
26.3.1.4
26.3.1.5
26.3.1.6
26.3.2
26.3.2.1
26.3.2.2
26.3.2.3
26.3.2.4
26.3.2.5
26.3.3
26.4
26.5
26.5.1
26.5.1.1
26.5.1.2
26.5.1.3
26.5.2
26.6
26.6.1
26.6.2
26.6.3
26.6.4
26.6.5
26.6.6
26.6.7
26.6.8
26.6.9
26.7
26.8
BASIC VM-ENTRY CHECKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-2
CHECKS ON VMX CONTROLS AND HOST-STATE AREA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-2
Checks on VMX Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-2
VM-Execution Control Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-2
VM-Exit Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-5
VM-Entry Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-5
Checks on Host Control Registers and MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-6
Checks on Host Segment and Descriptor-Table Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-7
Checks Related to Address-Space Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-7
CHECKING AND LOADING GUEST STATE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-7
Checks on the Guest State Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-8
Checks on Guest Control Registers, Debug Registers, and MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-8
Checks on Guest Segment Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-9
Checks on Guest Descriptor-Table Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-11
Checks on Guest RIP and RFLAGS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-11
Checks on Guest Non-Register State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-12
Checks on Guest Page-Directory-Pointer-Table Entries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-13
Loading Guest State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-14
Loading Guest Control Registers, Debug Registers, and MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-14
Loading Guest Segment Registers and Descriptor-Table Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-15
Loading Guest RIP, RSP, and RFLAGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-16
Loading Page-Directory-Pointer-Table Entries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-16
Updating Non-Register State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-16
Clearing Address-Range Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-17
LOADING MSRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-17
EVENT INJECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-17
Vectored-Event Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-18
Details of Vectored-Event Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-18
VM Exits During Event Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-19
Event Injection for VM Entries to Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-20
Injection of Pending MTF VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-20
SPECIAL FEATURES OF VM ENTRY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-20
Interruptibility State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-21
Activity State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-21
Delivery of Pending Debug Exceptions after VM Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-22
VMX-Preemption Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-23
Interrupt-Window Exiting and Virtual-Interrupt Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-23
NMI-Window Exiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-23
VM Exits Induced by the TPR Threshold. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-23
Pending MTF VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-24
VM Entries and Advanced Debugging Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26-24
VM-ENTRY FAILURES DURING OR AFTER LOADING GUEST STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-24
MACHINE-CHECK EVENTS DURING VM ENTRY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-25
CHAPTER 27
VM EXITS
27.1
27.2
27.2.1
27.2.2
27.2.3
27.2.4
27.3
27.3.1
27.3.2
27.3.3
27.3.4
27.4
27.5
27.5.1
27.5.2
ARCHITECTURAL STATE BEFORE A VM EXIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1
RECORDING VM-EXIT INFORMATION AND UPDATING VM-ENTRY CONTROL FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-3
Basic VM-Exit Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-4
Information for VM Exits Due to Vectored Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-10
Information for VM Exits During Event Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-11
Information for VM Exits Due to Instruction Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-12
SAVING GUEST STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-20
Saving Control Registers, Debug Registers, and MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-20
Saving Segment Registers and Descriptor-Table Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-21
Saving RIP, RSP, and RFLAGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-21
Saving Non-Register State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-23
SAVING MSRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-24
LOADING HOST STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-24
Loading Host Control Registers, Debug Registers, MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-25
Loading Host Segment and Descriptor-Table Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-26
xxii Vol. 3A
CONTENTS
PAGE
27.5.3
27.5.4
27.5.5
27.5.6
27.6
27.7
27.8
Loading Host RIP, RSP, and RFLAGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-27
Checking and Loading Host Page-Directory-Pointer-Table Entries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-27
Updating Non-Register State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-28
Clearing Address-Range Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-28
LOADING MSRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-28
VMX ABORTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-29
MACHINE-CHECK EVENTS DURING VM EXIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-29
CHAPTER 28
VMX SUPPORT FOR ADDRESS TRANSLATION
28.1
VIRTUAL PROCESSOR IDENTIFIERS (VPIDS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-1
28.2
THE EXTENDED PAGE TABLE MECHANISM (EPT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-1
28.2.1
EPT Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-1
28.2.2
EPT Translation Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-3
28.2.3
EPT-Induced VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-7
28.2.3.1
EPT Misconfigurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-7
28.2.3.2
EPT Violations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-8
28.2.3.3
Prioritization of EPT-Induced VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-10
28.2.4
Accessed and Dirty Flags for EPT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-11
28.2.5
EPT and Memory Typing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-11
28.2.5.1
Memory Type Used for Accessing EPT Paging Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-11
28.2.5.2
Memory Type Used for Translated Guest-Physical Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-12
28.3
CACHING TRANSLATION INFORMATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-12
28.3.1
Information That May Be Cached . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-13
28.3.2
Creating and Using Cached Translation Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-13
28.3.3
Invalidating Cached Translation Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-14
28.3.3.1
Operations that Invalidate Cached Mappings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-14
28.3.3.2
Operations that Need Not Invalidate Cached Mappings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-16
28.3.3.3
Guidelines for Use of the INVVPID Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-16
28.3.3.4
Guidelines for Use of the INVEPT Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-17
CHAPTER 29
APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS
29.1
29.1.1
29.1.2
29.1.3
29.1.4
29.1.5
29.2
29.2.1
29.2.2
29.3
29.4
29.4.1
29.4.2
29.4.3
29.4.3.1
29.4.3.2
29.4.3.3
29.4.4
29.4.5
29.4.6
29.4.6.1
29.4.6.2
29.5
29.6
VIRTUAL APIC STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-1
Virtualized APIC Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-1
TPR Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-2
PPR Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-2
EOI Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-3
Self-IPI Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-3
EVALUATION AND DELIVERY OF VIRTUAL INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-3
Evaluation of Pending Virtual Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-3
Virtual-Interrupt Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-4
VIRTUALIZING CR8-BASED TPR ACCESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-4
VIRTUALIZING MEMORY-MAPPED APIC ACCESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-5
Priority of APIC-Access VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-6
Virtualizing Reads from the APIC-Access Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-6
Virtualizing Writes to the APIC-Access Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-7
Determining Whether a Write Access is Virtualized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-7
APIC-Write Emulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-8
APIC-Write VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-9
Instruction-Specific Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-9
Issues Pertaining to Page Size and TLB Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-10
APIC Accesses Not Directly Resulting From Linear Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-10
Guest-Physical Accesses to the APIC-Access Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-11
Physical Accesses to the APIC-Access Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-11
VIRTUALIZING MSR-BASED APIC ACCESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-12
POSTED-INTERRUPT PROCESSING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-13
CHAPTER 30
VMX INSTRUCTION REFERENCE
30.1
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-1
Vol. 3A xxiii
CONTENTS
PAGE
30.2
30.3
30.4
CONVENTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-2
VMX INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-2
INVEPT— Invalidate Translations Derived from EPT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-3
INVVPID— Invalidate Translations Based on VPID. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-6
VMCALL—Call to VM Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-9
VMCLEAR—Clear Virtual-Machine Control Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30-11
VMFUNC—Invoke VM function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30-13
VMLAUNCH/VMRESUME—Launch/Resume Virtual Machine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30-14
VMPTRLD—Load Pointer to Virtual-Machine Control Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30-17
VMPTRST—Store Pointer to Virtual-Machine Control Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30-19
VMREAD—Read Field from Virtual-Machine Control Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30-21
VMRESUME—Resume Virtual Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30-23
VMWRITE—Write Field to Virtual-Machine Control Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30-24
VMXOFF—Leave VMX Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30-27
VMXON—Enter VMX Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30-29
VM INSTRUCTION ERROR NUMBERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-31
CHAPTER 31
VIRTUAL-MACHINE MONITOR PROGRAMMING CONSIDERATIONS
31.1
VMX SYSTEM PROGRAMMING OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-1
31.2
SUPPORTING PROCESSOR OPERATING MODES IN GUEST ENVIRONMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-1
31.2.1
Using Unrestricted Guest Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-1
31.3
MANAGING VMCS REGIONS AND POINTERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-2
31.4
USING VMX INSTRUCTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-2
31.5
VMM SETUP & TEAR DOWN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-4
31.5.1
Algorithms for Determining VMX Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-5
31.6
PREPARATION AND LAUNCHING A VIRTUAL MACHINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-6
31.7
HANDLING OF VM EXITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-7
31.7.1
Handling VM Exits Due to Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-8
31.7.1.1
Reflecting Exceptions to Guest Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-8
31.7.1.2
Resuming Guest Software after Handling an Exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-9
31.8
MULTI-PROCESSOR CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-10
31.8.1
Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-11
31.8.2
Moving a VMCS Between Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-11
31.8.3
Paired Index-Data Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-11
31.8.4
External Data Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-11
31.8.5
CPUID Emulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-12
31.9
32-BIT AND 64-BIT GUEST ENVIRONMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-12
31.9.1
Operating Modes of Guest Environments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-12
31.9.2
Handling Widths of VMCS Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-12
31.9.2.1
Natural-Width VMCS Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-13
31.9.2.2
64-Bit VMCS Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-13
31.9.3
IA-32e Mode Hosts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-13
31.9.4
IA-32e Mode Guests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-13
31.9.5
32-Bit Guests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-14
31.10 HANDLING MODEL SPECIFIC REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-14
31.10.1
Using VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-14
31.10.2
Using VM-Exit Controls for MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-15
31.10.3
Using VM-Entry Controls for MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-15
31.10.4
Handling Special-Case MSRs and Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-15
31.10.4.1
Handling IA32_EFER MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-16
31.10.4.2
Handling the SYSENTER and SYSEXIT Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-16
31.10.4.3
Handling the SYSCALL and SYSRET Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-16
31.10.4.4
Handling the SWAPGS Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-16
31.10.4.5
Implementation Specific Behavior on Writing to Certain MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-16
31.10.5
Handling Accesses to Reserved MSR Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-17
31.11 HANDLING ACCESSES TO CONTROL REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-17
31.12 PERFORMANCE CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-17
31.13 USE OF THE VMX-PREEMPTION TIMER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-17
xxiv Vol. 3A
CONTENTS
PAGE
CHAPTER 32
VIRTUALIZATION OF SYSTEM RESOURCES
32.1
32.2
32.2.1
32.3
32.3.1
32.3.2
32.3.3
32.3.4
32.3.5
32.3.5.1
32.3.5.2
32.3.5.3
32.3.5.4
32.4
32.4.1
32.4.2
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-1
VIRTUALIZATION SUPPORT FOR DEBUGGING FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-1
Debug Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-1
MEMORY VIRTUALIZATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-2
Processor Operating Modes & Memory Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-2
Guest & Host Physical Address Spaces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-2
Virtualizing Virtual Memory by Brute Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-3
Alternate Approach to Memory Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-3
Details of Virtual TLB Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-4
Initialization of Virtual TLB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-5
Response to Page Faults. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-5
Response to Uses of INVLPG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-7
Response to CR3 Writes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-8
MICROCODE UPDATE FACILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-8
Early Load of Microcode Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-8
Late Load of Microcode Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-8
CHAPTER 33
HANDLING BOUNDARY CONDITIONS IN A VIRTUAL MACHINE MONITOR
33.1
33.2
33.3
33.3.1
33.3.2
33.3.2.1
33.3.2.2
33.3.2.3
33.3.2.4
33.3.2.5
33.3.3
33.3.3.1
33.3.3.2
33.3.3.3
33.3.3.4
33.4
33.4.1
33.4.2
33.4.3
33.4.3.1
33.4.3.2
33.4.3.3
33.4.3.4
33.4.3.5
33.5
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-1
INTERRUPT HANDLING IN VMX OPERATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-1
EXTERNAL INTERRUPT VIRTUALIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-2
Virtualization of Interrupt Vector Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-3
Control of Platform Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-4
PIC Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-4
xAPIC Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-5
Local APIC Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-5
I/O APIC Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-6
Virtualization of Message Signaled Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-6
Examples of Handling of External Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-6
Guest Setup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-6
Processor Treatment of External Interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-6
Processing of External Interrupts by VMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-7
Generation of Virtual Interrupt Events by VMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-7
ERROR HANDLING BY VMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-8
VM-Exit Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-8
Machine-Check Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-8
MCA Error Handling Guidelines for VMM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-9
VMM Error Handling Strategies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-10
Basic VMM MCA error recovery handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-10
Implementation Considerations for the Basic Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-10
MCA Virtualization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-10
Implementation Considerations for the MCA Virtualization Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-11
HANDLING ACTIVITY STATES BY VMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-11
CHAPTER 34
SYSTEM MANAGEMENT MODE
34.1
34.1.1
34.2
34.3
SYSTEM MANAGEMENT MODE OVERVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1
System Management Mode and VMX Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1
SYSTEM MANAGEMENT INTERRUPT (SMI). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-2
SWITCHING BETWEEN SMM AND THE OTHER
PROCESSOR OPERATING MODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-2
34.3.1
Entering SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-2
34.3.2
Exiting From SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-3
34.4
SMRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-3
34.4.1
SMRAM State Save Map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-4
34.4.1.1
SMRAM State Save Map and Intel 64 Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-6
34.4.2
SMRAM Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-8
34.4.2.1
System Management Range Registers (SMRR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-9
34.5
SMI HANDLER EXECUTION ENVIRONMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-9
Vol. 3A xxv
CONTENTS
PAGE
34.5.1
34.5.2
34.6
34.7
Initial SMM Execution Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-9
SMI Handler Operating Mode Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-10
EXCEPTIONS AND INTERRUPTS WITHIN SMM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-10
MANAGING SYNCHRONOUS AND ASYNCHRONOUS
SYSTEM MANAGEMENT INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-11
34.7.1
I/O State Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-12
34.8
NMI HANDLING WHILE IN SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-13
34.9
SMM REVISION IDENTIFIER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-13
34.10 AUTO HALT RESTART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-13
34.10.1
Executing the HLT Instruction in SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-14
34.11 SMBASE RELOCATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-14
34.12 I/O INSTRUCTION RESTART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-15
34.12.1
Back-to-Back SMI Interrupts When I/O Instruction Restart Is Being Used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-16
34.13 SMM MULTIPLE-PROCESSOR CONSIDERATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-16
34.14 DEFAULT TREATMENT OF SMIS AND SMM WITH VMX OPERATION AND SMX OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . 34-16
34.14.1
Default Treatment of SMI Delivery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-16
34.14.2
Default Treatment of RSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-17
34.14.3
Protection of CR4.VMXE in SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-18
34.14.4
VMXOFF and SMI Unblocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-18
34.15 DUAL-MONITOR TREATMENT OF SMIs AND SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-19
34.15.1
Dual-Monitor Treatment Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-19
34.15.2
SMM VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-19
34.15.2.1
Architectural State Before a VM Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-20
34.15.2.2
Updating the Current-VMCS and Executive-VMCS Pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-20
34.15.2.3
Recording VM-Exit Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-20
34.15.2.4
Saving Guest State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-21
34.15.2.5
Updating Non-Register State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-21
34.15.3
Operation of the SMM-Transfer Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-21
34.15.4
VM Entries that Return from SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-22
34.15.4.1
Checks on the Executive-VMCS Pointer Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-22
34.15.4.2
Checks on VM-Execution Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-22
34.15.4.3
Checks on VM-Entry Control Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-22
34.15.4.4
Checks on the Guest State Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-23
34.15.4.5
Loading Guest State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-23
34.15.4.6
VMX-Preemption Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-23
34.15.4.7
Updating the Current-VMCS and SMM-Transfer VMCS Pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-23
34.15.4.8
VM Exits Induced by VM Entry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-24
34.15.4.9
SMI Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-24
34.15.4.10
Failures of VM Entries That Return from SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-24
34.15.5
Enabling the Dual-Monitor Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-24
34.15.6
Activating the Dual-Monitor Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-26
34.15.6.1
Initial Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-26
34.15.6.2
MSEG Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-26
34.15.6.3
Updating the Current-VMCS and Executive-VMCS Pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-27
34.15.6.4
Saving Guest State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-27
34.15.6.5
Saving MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-27
34.15.6.6
Loading Host State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-27
34.15.6.7
Loading MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-29
34.15.7
Deactivating the Dual-Monitor Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-29
34.16 SMI AND PROCESSOR EXTENDED STATE MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-29
CHAPTER 35
MODEL-SPECIFIC REGISTERS (MSRS)
35.1
35.2
35.3
35.4
35.4.1
35.4.2
35.5
35.6
35.7
ARCHITECTURAL MSRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-2
MSRS IN THE INTEL® CORE™ 2 PROCESSOR FAMILY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-28
MSRS IN THE INTEL® ATOM™ PROCESSOR FAMILY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-42
MSRS IN THE INTEL® MICROARCHITECTURE CODE NAME NEHALEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-53
Additional MSRs in the Intel® Xeon® Processor 5500 and 3400 Series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-69
Additional MSRs in the Intel® Xeon® Processor 7500 Series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-71
MSRS IN THE INTEL® XEON® PROCESSOR 5600 SERIES (BASED ON INTEL® MICROARCHITECTURE CODE NAME WESTMERE)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-86
MSRS IN THE INTEL® XEON® PROCESSOR E7 FAMILY (BASED ON INTEL® MICROARCHITECTURE CODE NAME WESTMERE)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-87
MSRS IN INTEL® PROCESSOR FAMILY (BASED ON INTEL® MICROARCHITECTURE CODE NAME SANDY BRIDGE) . . . . . 35-88
xxvi Vol. 3A
CONTENTS
PAGE
®
35.7.1
MSRs In 2nd Generation Intel Core™ Processor Family (Based on Intel® Microarchitecture Code Name Sandy Bridge) . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-104
35.7.2
MSRs In Intel® Xeon® Processor E5 Family (Based on Intel® Microarchitecture Code Name Sandy Bridge). . . . . 35-107
35.8
MSRS IN THE 3RD GENERATION INTEL® CORE™ PROCESSOR FAMILY (BASED ON INTEL® MICROARCHITECTURE CODE NAME IVY
BRIDGE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-110
35.8.1
MSRs In Intel® Xeon® Processor E5 Family v2 (Based on Intel® Microarchitecture Code Name Ivy Bridge). . . . . 35-112
35.9
MSRS IN THE NEXT GENERATION INTEL® CORE™ PROCESSORS (BASED ON INTEL® MICROARCHITECTURE CODE NAME
HASWELL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-115
35.10 MSRS IN FUTURE GENERATION INTEL® XEON® PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-115
35.11 MSRS IN THE PENTIUM® 4 AND INTEL® XEON® PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-116
35.11.1
MSRs Unique to Intel® Xeon® Processor MP with L3 Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-141
35.12 MSRS IN INTEL® CORE™ SOLO AND INTEL® CORE™ DUO PROCESSORS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-143
35.13 MSRS IN THE PENTIUM M PROCESSOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-152
35.14 MSRS IN THE P6 FAMILY PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-158
35.15 MSRS IN PENTIUM PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-167
APPENDIX A
VMX CAPABILITY REPORTING FACILITY
A.1
A.2
A.3
A.3.1
A.3.2
A.3.3
A.4
A.5
A.6
A.7
A.8
A.9
A.10
A.11
BASIC VMX INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RESERVED CONTROLS AND DEFAULT SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VM-EXECUTION CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pin-Based VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Primary Processor-Based VM-Execution Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Secondary Processor-Based VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VM-EXIT CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VM-ENTRY CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MISCELLANEOUS DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VMX-FIXED BITS IN CR0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VMX-FIXED BITS IN CR4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VMCS ENUMERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VPID AND EPT CAPABILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VM FUNCTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
APPENDIX B
FIELD ENCODING IN VMCS
B.1
B.1.1
B.1.2
B.1.3
B.2
B.2.1
B.2.2
B.2.3
B.2.4
B.3
B.3.1
B.3.2
B.3.3
B.3.4
B.4
B.4.1
B.4.2
B.4.3
B.4.4
16-BIT FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16-Bit Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16-Bit Guest-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16-Bit Host-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
64-BIT FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
64-Bit Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
64-Bit Read-Only Data Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
64-Bit Guest-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
64-Bit Host-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32-BIT FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32-Bit Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32-Bit Read-Only Data Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32-Bit Guest-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32-Bit Host-State Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
NATURAL-WIDTH FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Natural-Width Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Natural-Width Read-Only Data Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Natural-Width Guest-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Natural-Width Host-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A-1
A-2
A-2
A-3
A-3
A-4
A-4
A-5
A-5
A-6
A-6
A-7
A-7
A-8
B-1
B-1
B-1
B-2
B-2
B-2
B-4
B-4
B-5
B-5
B-5
B-6
B-6
B-7
B-7
B-8
B-8
B-8
B-9
APPENDIX C
VMX BASIC EXIT REASONS
Vol. 3A xxvii
CONTENTS
PAGE
FIGURES
Figure 1-1.
Figure 1-2.
Figure 2-1.
Figure 2-2.
Figure 2-3.
Figure 2-4.
Figure 2-5.
Figure 2-6.
Figure 2-7.
Figure 2-8.
Figure 2-9.
Figure 3-1.
Figure 3-2.
Figure 3-3.
Figure 3-4.
Figure 3-5.
Figure 3-6.
Figure 3-7.
Figure 3-8.
Figure 3-9.
Figure 3-10.
Figure 3-11.
Figure 4-1.
Figure 4-2.
Figure 4-3.
Figure 4-4.
Figure 4-5.
Figure 4-6.
Figure 4-7.
Figure 4-8.
Figure 4-9.
Figure 4-10.
Figure 4-11.
Figure 4-12.
Figure 4-13.
Figure 5-1.
Figure 5-2.
Figure 5-3.
Figure 5-4.
Figure 5-5.
Figure 5-6.
Figure 5-7.
Figure 5-8.
Figure 5-9.
Figure 5-10.
Figure 5-11.
Figure 5-12.
Figure 5-13.
Figure 5-14.
Figure 5-15.
Figure 6-1.
Figure 6-2.
Figure 6-3.
Figure 6-4.
Figure 6-5.
Figure 6-6.
Figure 6-7.
Figure 6-8.
Figure 6-9.
Figure 7-1.
Figure 7-2.
xxviii Vol. 3A
Bit and Byte Order. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-6
Syntax for CPUID, CR, and MSR Data Presentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-7
IA-32 System-Level Registers and Data Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-2
System-Level Registers and Data Structures in IA-32e Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-3
Transitions Among the Processor’s Operating Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-8
IA32_EFER MSR Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-9
System Flags in the EFLAGS Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10
Memory Management Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12
Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14
XCR0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19
WBINVD Invalidation of Shared and Non-Shared Cache Hierarchy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23
Segmentation and Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2
Flat Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3
Protected Flat Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4
Multi-Segment Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-5
Logical Address to Linear Address Translation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-7
Segment Selector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-7
Segment Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-8
Segment Descriptor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10
Segment Descriptor When Segment-Present Flag Is Clear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11
Global and Local Descriptor Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15
Pseudo-Descriptor Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16
Enabling and Changing Paging Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3
Linear-Address Translation to a 4-KByte Page using 32-Bit Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-9
Linear-Address Translation to a 4-MByte Page using 32-Bit Paging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-9
Formats of CR3 and Paging-Structure Entries with 32-Bit Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10
Linear-Address Translation to a 4-KByte Page using PAE Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15
Linear-Address Translation to a 2-MByte Page using PAE Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16
Formats of CR3 and Paging-Structure Entries with PAE Paging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18
Linear-Address Translation to a 4-KByte Page using IA-32e Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-20
Linear-Address Translation to a 2-MByte Page using IA-32e Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-21
Linear-Address Translation to a 1-GByte Page using IA-32e Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-21
Formats of CR3 and Paging-Structure Entries with IA-32e Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-28
Page-Fault Error Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-30
Memory Management Convention That Assigns a Page Table
to Each Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-45
Descriptor Fields Used for Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-3
Descriptor Fields with Flags used in IA-32e Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-4
Protection Rings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-7
Privilege Check for Data Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-8
Examples of Accessing Data Segments From Various Privilege Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-9
Privilege Check for Control Transfer Without Using a Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11
Examples of Accessing Conforming and Nonconforming Code Segments From Various Privilege Levels . . . . . . . . . . 5-12
Call-Gate Descriptor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13
Call-Gate Descriptor in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14
Call-Gate Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15
Privilege Check for Control Transfer with Call Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16
Example of Accessing Call Gates At Various Privilege Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17
Stack Switching During an Interprivilege-Level Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19
MSRs Used by SYSCALL and SYSRET. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23
Use of RPL to Weaken Privilege Level of Called Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26
Relationship of the IDTR and IDT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10
IDT Gate Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11
Interrupt Procedure Call. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12
Stack Usage on Transfers to Interrupt and Exception-Handling Routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13
Interrupt Task Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15
Error Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16
64-Bit IDT Gate Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17
IA-32e Mode Stack Usage After Privilege Level Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-19
Page-Fault Error Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-41
Structure of a Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-2
32-Bit Task-State Segment (TSS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-4
CONTENTS
PAGE
Figure 7-3.
Figure 7-4.
Figure 7-5.
Figure 7-6.
Figure 7-7.
Figure 7-8.
Figure 7-9.
Figure 7-10.
Figure 7-11.
Figure 8-1.
Figure 8-2.
Figure 8-3.
Figure 8-4.
Figure 8-5.
Figure 8-6.
Figure 8-7.
Figure 8-1.
Figure 9-1.
Figure 9-2.
Figure 9-3.
Figure 9-4.
Figure 9-5.
Figure 9-6.
Figure 9-7.
Figure 9-8.
Figure 9-9.
Figure 10-1.
Figure 10-2.
Figure 10-3.
Figure 10-4.
Figure 10-5.
Figure 10-6.
Figure 10-7.
Figure 10-8.
Figure 10-9.
Figure 10-10.
Figure 10-11.
Figure 10-12.
Figure 10-13.
Figure 10-14.
Figure 10-15.
Figure 10-16.
Figure 10-17.
Figure 10-18.
Figure 10-19.
Figure 10-20.
Figure 10-21.
Figure 10-22.
Figure 10-23.
Figure 10-24.
Figure 10-25.
Figure 10-26.
Figure 10-27.
Figure 10-28.
Figure 10-29.
Figure 10-30.
Figure 11-1.
Figure 11-2.
Figure 11-3.
Figure 11-4.
Figure 11-5.
Figure 11-6.
Figure 11-7.
Figure 11-8.
Figure 11-9.
TSS Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6
Format of TSS and LDT Descriptors in 64-bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7
Task Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8
Task-Gate Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8
Task Gates Referencing the Same Task. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9
Nested Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12
Overlapping Linear-to-Physical Mappings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15
16-Bit TSS Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16
64-Bit TSS Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17
Example of Write Ordering in Multiple-Processor Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7
Interpretation of APIC ID in Early MP Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23
Local APICs and I/O APIC in MP System Supporting Intel HT Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-26
IA-32 Processor with Two Logical Processors Supporting Intel HT Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-27
Generalized Four level Interpretation of the APIC ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-34
Conceptual Five-level Topology and 32-bit APIC ID Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-34
Topological Relationships between Hierarchical IDs in a Hypothetical MP Platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-36
MP System With Multiple Pentium III Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-54
Contents of CR0 Register after Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4
Version Information in the EDX Register after Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5
Processor State After Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15
Constructing Temporary GDT and Switching to Protected Mode (Lines 162-172 of List File). . . . . . . . . . . . . . . . . . . . 9-23
Moving the GDT, IDT, and TSS from ROM to RAM (Lines 196-261 of List File) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-24
Task Switching (Lines 282-296 of List File) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25
Applying Microcode Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-28
Microcode Update Write Operation Flow [1]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-45
Microcode Update Write Operation Flow [2]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-46
Relationship of Local APIC and I/O APIC In Single-Processor Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2
Local APICs and I/O APIC When Intel Xeon Processors Are Used in Multiple-Processor Systems . . . . . . . . . . . . . . . . . 10-3
Local APICs and I/O APIC When P6 Family Processors Are Used in Multiple-Processor Systems. . . . . . . . . . . . . . . . . . 10-3
Local APIC Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-5
IA32_APIC_BASE MSR (APIC_BASE_MSR in P6 Family). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-9
Local APIC ID Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10
Local APIC Version Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12
Local Vector Table (LVT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-13
Error Status Register (ESR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-15
Divide Configuration Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-16
Initial Count and Current Count Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-17
Interrupt Command Register (ICR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-20
Logical Destination Register (LDR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-24
Destination Format Register (DFR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-24
Arbitration Priority Register (APR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-25
Interrupt Acceptance Flow Chart for the Local APIC (Pentium 4 and Intel Xeon Processors). . . . . . . . . . . . . . . . . . . . 10-27
Interrupt Acceptance Flow Chart for the Local APIC (P6 Family and Pentium Processors) . . . . . . . . . . . . . . . . . . . . . . 10-28
Task-Priority Register (TPR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-29
Processor-Priority Register (PPR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-29
IRR, ISR and TMR Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-30
EOI Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-31
CR8 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-32
Spurious-Interrupt Vector Register (SVR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-33
Layout of the MSI Message Address Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-34
Layout of the MSI Message Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-36
IA32_APIC_BASE MSR Supporting x2APIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-37
Local x2APIC State Transitions with IA32_APIC_BASE, INIT, and Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-42
Interrupt Command Register (ICR) in x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-45
Logical Destination Register in x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-46
SELF IPI register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-47
Cache Structure of the Pentium 4 and Intel Xeon Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1
Cache Structure of the Intel Core i7 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2
Cache-Control Registers and Bits Available in Intel 64 and IA-32 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-11
Mapping Physical Memory With MTRRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-21
IA32_MTRRCAP Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-22
IA32_MTRR_DEF_TYPE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-23
IA32_MTRR_PHYSBASEn and IA32_MTRR_PHYSMASKn Variable-Range Register Pair . . . . . . . . . . . . . . . . . . . . . . . . 11-25
IA32_SMRR_PHYSBASE and IA32_SMRR_PHYSMASK SMRR Pair. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-26
IA32_PAT MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-34
Vol. 3A xxix
CONTENTS
PAGE
Figure 12-1.
Figure 12-2.
Figure 13-1.
Figure 13-2.
Figure 13-3.
Figure 13-4.
Figure 14-1.
Figure 14-2.
Figure 14-3.
Figure 14-4.
Figure 14-5.
Figure 14-6.
Figure 14-7.
Figure 14-8.
Figure 14-9.
Figure 14-10.
Figure 14-11.
Figure 14-12.
Figure 14-13.
Figure 14-14.
Figure 14-15.
Figure 14-16.
Figure 14-17.
Figure 14-18.
Figure 14-19.
Figure 14-20.
Figure 14-21.
Figure 14-22.
Figure 14-23.
Figure 14-24.
Figure 14-25.
Figure 14-26.
Figure 14-27.
Figure 14-28.
Figure 15-1.
Figure 15-2.
Figure 15-3.
Figure 15-4.
Figure 15-5.
Figure 15-6.
Figure 15-7.
Figure 15-8.
Figure 15-9.
Figure 17-1.
Figure 17-2.
Figure 17-3.
Figure 17-4.
Figure 17-5.
Figure 17-6.
Figure 17-7.
Figure 17-8.
Figure 17-9.
Figure 17-10.
Figure 17-11.
Figure 17-12.
Figure 17-13.
Figure 17-14.
Figure 17-15.
xxx Vol. 3A
Mapping of MMX Registers to Floating-Point Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2
Mapping of MMX Registers to x87 FPU Data Register Stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5
Example of Saving the x87 FPU, MMX, SSE, SSE2, SSE3, and SSSE3 State During an Operating-System Controlled Task
Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-7
Future Layout of XSAVE/XRSTOR Area and XSTATE_BV with Five Sets of Processor State Extensions . . . . . . . . . 13-9
OS Enabling of Processor Extended State Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-11
Application Detection of New Instruction Extensions and Processor Extended State . . . . . . . . . . . . . . . . . . . . . . . . . . 13-12
IA32_MPERF MSR and IA32_APERF MSR for P-state Coordination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-2
IA32_PERF_CTL Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4
Periodic Query of Activity Ratio of Opportunistic Processor Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-5
IA32_ENERGY_PERF_BIAS Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-6
Processor Modulation Through Stop-Clock Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-8
MSR_THERM2_CTL Register On Processors with CPUID Family/Model/Stepping Signature Encoded as 0x69n or 0x6Dn
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-9
MSR_THERM2_CTL Register for Supporting TM2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-10
IA32_THERM_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-10
IA32_THERM_INTERRUPT MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-11
IA32_CLOCK_MODULATION MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-12
IA32_CLOCK_MODULATION MSR with Clock Modulation Extension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-13
IA32_THERM_STATUS Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-14
IA32_THERM_INTERRUPT Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-15
IA32_PACKAGE_THERM_STATUS Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-17
IA32_PACKAGE_THERM_INTERRUPT Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-18
MSR_RAPL_POWER_UNIT Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-20
MSR_PKG_POWER_LIMIT Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-21
MSR_PKG_ENERGY_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-22
MSR_PKG_POWER_INFO Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-22
MSR_PKG_PERF_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-23
MSR_PP0_POWER_LIMIT/MSR_PP1_POWER_LIMIT Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-24
MSR_PP0_ENERGY_STATUS/MSR_PP1_ENERGY_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-24
MSR_PP0_POLICY/MSR_PP1_POLICY Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-25
MSR_PP0_PERF_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-25
MSR_DRAM_POWER_LIMIT Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-26
MSR_DRAM_ENERGY_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-26
MSR_DRAM_POWER_INFO Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-27
MSR_DRAM_PERF_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-27
Machine-Check MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-2
IA32_MCG_CAP Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-2
IA32_MCG_STATUS Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
IA32_MCi_CTL Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-4
IA32_MCi_STATUS Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-5
IA32_MCi_ADDR MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-7
UCR Support in IA32_MCi_MISC Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-8
IA32_MCi_CTL2 Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-9
CMCI Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-12
Debug Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-2
DR6/DR7 Layout on Processors Supporting Intel® 64 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-6
IA32_DEBUGCTL MSR for Processors based
on Intel Core microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-11
64-bit Address Layout of LBR MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-14
DS Save Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-16
32-bit Branch Trace Record Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-17
PEBS Record Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-17
IA-32e Mode DS Save Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-18
64-bit Branch Trace Record Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-18
64-bit PEBS Record Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-19
IA32_DEBUGCTL MSR for Processors based
on Intel microarchitecture code name Nehalem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-24
MSR_DEBUGCTLA MSR for Pentium 4 and Intel Xeon Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-28
LBR MSR Branch Record Layout for the Pentium 4
and Intel Xeon Processor Family. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-30
IA32_DEBUGCTL MSR for Intel Core Solo
and Intel Core Duo Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-31
LBR Branch Record Layout for the Intel Core Solo
and Intel Core Duo Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-31
CONTENTS
PAGE
Figure 17-16.
Figure 17-17.
Figure 17-18.
Figure 17-19.
Figure 17-20.
Figure 17-21.
Figure 18-1.
Figure 18-2.
Figure 18-3.
Figure 18-4.
Figure 18-5.
Figure 18-6.
Figure 18-7.
Figure 18-8.
Figure 18-9.
Figure 18-10.
Figure 18-11.
Figure 18-12.
Figure 18-13.
Figure 18-14.
Figure 18-15.
Figure 18-16.
Figure 18-17.
Figure 18-18.
Figure 18-19.
Figure 18-20.
Figure 18-21.
Figure 18-22.
Figure 18-23.
Figure 18-24.
Figure 18-25.
Figure 18-26.
Figure 18-27.
Figure 18-28.
Figure 18-29.
Figure 18-30.
Figure 18-31.
Figure 18-32.
Figure 18-33.
Figure 18-34.
Figure 18-35.
Figure 18-36.
Figure 18-37.
Figure 18-38.
Figure 18-39.
Figure 18-40.
Figure 18-41.
Figure 18-42.
Figure 18-43.
Figure 18-44.
Figure 18-45.
Figure 18-46.
Figure 18-47.
Figure 18-48.
Figure 18-49.
Figure 18-50.
Figure 18-51.
Figure 18-52.
Figure 18-53.
Figure 20-1.
Figure 20-2.
Figure 20-3.
MSR_DEBUGCTLB MSR for Pentium M Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-32
LBR Branch Record Layout for the Pentium M Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-33
DEBUGCTLMSR Register (P6 Family Processors). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-34
CPUID.(EAX=0FH, ECX=0H) QoS Resource Type Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-38
L3 Cache QoS Monitoring Capability Enumeration (CPUID.(EAX=0FH, ECX=1H) ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-38
IA32_PQR_ASSOC, IA32_QM_EVTSEL and IA32_QM_CTR MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-39
Layout of IA32_PERFEVTSELx MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-3
Layout of IA32_FIXED_CTR_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-5
Layout of IA32_PERF_GLOBAL_CTRL MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-6
Layout of IA32_PERF_GLOBAL_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-6
Layout of IA32_PERF_GLOBAL_OVF_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-7
Layout of IA32_PERFEVTSELx MSRs Supporting Architectural Performance Monitoring Version 3 . . . . . . . . . . . . . . 18-7
Layout of IA32_FIXED_CTR_CTRL MSR Supporting Architectural Performance Monitoring Version 3 . . . . . . . . . . . . 18-8
Layout of Global Performance Monitoring Control MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-8
Global Performance Monitoring Overflow Status and Control MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-9
Layout of MSR_PERF_FIXED_CTR_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-14
Layout of MSR_PERF_GLOBAL_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-15
Layout of MSR_PERF_GLOBAL_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-15
Layout of MSR_PERF_GLOBAL_OVF_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-16
IA32_PERF_GLOBAL_STATUS MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-20
Layout of IA32_PEBS_ENABLE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-21
PEBS Programming Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-23
Layout of MSR_PEBS_LD_LAT MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-26
Layout of MSR_OFFCORE_RSP_0 and MSR_OFFCORE_RSP_1 to Configure Off-core Response Events . . . . . . . . . 18-27
Layout of MSR_UNCORE_PERF_GLOBAL_CTRL MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-29
Layout of MSR_UNCORE_PERF_GLOBAL_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-30
Layout of MSR_UNCORE_PERF_GLOBAL_OVF_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-30
Layout of MSR_UNCORE_PERFEVTSELx MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-31
Layout of MSR_UNCORE_FIXED_CTR_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-32
Layout of MSR_UNCORE_ADDR_OPCODE_MATCH MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-32
Distributed Units of the Uncore of Intel® Xeon® Processor 7500 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-34
IA32_PERF_GLOBAL_CTRL MSR in Intel® Microarchitecture Code Name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . . . . . 18-37
IA32_PERF_GLOBAL_STATUS MSR in Intel® Microarchitecture Code Name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . . 18-37
IA32_PERF_GLOBAL_OVF_CTRL MSR in Intel microarchitecture code name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . 18-38
Layout of IA32_PEBS_ENABLE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-40
Request_Type Fields for MSR_OFFCORE_RSP_x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-44
Response_Supplier and Snoop Info Fields for MSR_OFFCORE_RSP_x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-45
Layout of Uncore PERFEVTSEL MSR for a C-Box Unit or the ARB Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-46
Layout of MSR_UNC_PERF_GLOBAL_CTRL MSR for Uncore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-47
Layout of IA32_PERFEVTSELx MSRs Supporting Intel TSX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-54
Event Selection Control Register (ESCR) for Pentium 4
and Intel Xeon Processors without Intel HT Technology Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-59
Performance Counter (Pentium 4 and Intel Xeon Processors) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-61
Counter Configuration Control Register (CCCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-62
Effects of Edge Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-66
Event Selection Control Register (ESCR) for the Pentium 4 Processor, Intel Xeon Processor and Intel Xeon Processor MP
Supporting Hyper-Threading Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-73
Counter Configuration Control Register (CCCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-75
Layout of IA32_PERF_CAPABILITIES MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-80
Block Diagram of 64-bit Intel Xeon Processor MP with 8-MByte L3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-81
MSR_IFSB_IBUSQx, Addresses: 107CCH and 107CDH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-81
MSR_IFSB_ISNPQx, Addresses: 107CEH and 107CFH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-82
MSR_EFSB_DRDYx, Addresses: 107D0H and 107D1H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-82
MSR_IFSB_CTL6, Address: 107D2H;
MSR_IFSB_CNTR7, Address: 107D3H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-83
Block Diagram of Intel Xeon Processor 7400 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-84
Block Diagram of Intel Xeon Processor 7100 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-85
MSR_EMON_L3_CTR_CTL0/1, Addresses: 107CCH/107CDH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-86
MSR_EMON_L3_CTR_CTL2/3, Addresses: 107CEH/107CFH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-88
MSR_EMON_L3_CTR_CTL4/5/6/7, Addresses: 107D0H-107D3H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-88
PerfEvtSel0 and PerfEvtSel1 MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-90
CESR MSR (Pentium Processor Only). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-93
Real-Address Mode Address Translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-3
Interrupt Vector Table in Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-5
Entering and Leaving Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-9
Vol. 3A xxxi
CONTENTS
PAGE
Figure 20-4.
Figure 20-5.
Figure 21-1.
Figure 22-1.
Figure 23-1.
Figure 24-1.
Figure 28-1.
Figure 30-1.
Figure 30-2.
Figure 31-1.
Figure 32-1.
Figure 33-1.
Figure 34-1.
Figure 34-2.
Figure 34-3.
Figure 34-4.
Figure 34-5.
xxxii Vol. 3A
Privilege Level 0 Stack After Interrupt or
Exception in Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-13
Software Interrupt Redirection Bit Map in TSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-18
Stack after Far 16- and 32-Bit Calls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-5
I/O Map Base Address Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-29
Interaction of a Virtual-Machine Monitor and Guests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-2
States of VMCS X. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-2
Formats of EPTP and EPT Paging-Structure Entries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-9
INVEPT Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-3
INVVPID Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-6
VMX Transitions and States of VMCS in a Logical Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-3
Virtual TLB Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-5
Host External Interrupts and Guest Virtual Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-4
SMRAM Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-4
SMM Revision Identifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-13
Auto HALT Restart Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-14
SMBASE Relocation Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-15
I/O Instruction Restart Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-15
CONTENTS
PAGE
TABLES
Table 2-1.
Table 2-2.
Table 2-3.
Table 3-1.
Table 3-2.
Table 4-1.
Table 4-2.
Table 4-3.
Table 4-4.
Table 4-6.
Table 4-5.
Table 4-7.
Table 4-8.
Table 4-9.
Table 4-10.
Table 4-11.
Table 4-12.
Table 4-13.
Table 4-14.
Table 4-15.
Table 4-16.
Table 4-17.
Table 4-18.
Table 4-19.
Table 5-1.
Table 5-2.
Table 5-3.
Table 5-4.
Table 5-6.
Table 5-7.
Table 5-5.
Table 5-9.
Table 5-8.
Table 6-1.
Table 6-2.
Table 6-3.
Table 6-4.
Table 6-5.
Table 6-6.
Table 6-7.
Table 6-8.
Table 7-1.
Table 7-2.
Table 8-1.
Table 8-2.
Table 8-3.
Table 8-4.
Table 9-1.
Table 9-2.
Table 9-3.
Table 9-4.
Table 9-5.
Table 9-6.
Table 9-7.
Table 9-8.
Table 9-9.
IA32_EFER MSR Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-9
Action Taken By x87 FPU Instructions for Different Combinations of EM, MP, and TS . . . . . . . . . . . . . . . . . . . . . . . . . . 2-16
Summary of System Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20
Code- and Data-Segment Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12
System-Segment and Gate-Descriptor Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14
Properties of Different Paging Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2
Paging Structures in the Different Paging Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-7
Use of CR3 with 32-Bit Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10
Format of a 32-Bit Page-Directory Entry that Maps a 4-MByte Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11
Format of a 32-Bit Page-Table Entry that Maps a 4-KByte Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12
Format of a 32-Bit Page-Directory Entry that References a Page Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12
Use of CR3 with PAE Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13
Format of a PAE Page-Directory-Pointer-Table Entry (PDPTE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14
Format of a PAE Page-Directory Entry that Maps a 2-MByte Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16
Format of a PAE Page-Directory Entry that References a Page Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17
Format of a PAE Page-Table Entry that Maps a 4-KByte Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17
Use of CR3 with IA-32e Paging and CR4.PCIDE = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19
Use of CR3 with IA-32e Paging and CR4.PCIDE = 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19
Format of an IA-32e PML4 Entry (PML4E) that References a Page-Directory-Pointer Table. . . . . . . . . . . . . . . . . . . . . 4-23
Format of an IA-32e Page-Directory-Pointer-Table Entry (PDPTE) that Maps a 1-GByte Page. . . . . . . . . . . . . . . . . . . 4-24
Format of an IA-32e Page-Directory-Pointer-Table Entry (PDPTE) that References a Page Directory. . . . . . . . . . . . 4-25
Format of an IA-32e Page-Directory Entry that Maps a 2-MByte Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-25
Format of an IA-32e Page-Directory Entry that References a Page Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-26
Format of an IA-32e Page-Table Entry that Maps a 4-KByte Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-27
Privilege Check Rules for Call Gates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16
64-Bit-Mode Stack Layout After CALLF with CPL Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19
Combined Page-Directory and Page-Table Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29
Extended Feature Enable MSR (IA32_EFER). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30
Legacy PAE-Enabled 4-KByte Page Level Protection Matrix
with Execute-Disable Bit Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31
Legacy PAE-Enabled 2-MByte Page Level Protection
with Execute-Disable Bit Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31
IA-32e Mode Page Level Protection Matrix
with Execute-Disable Bit Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31
Reserved Bit Checking WIth Execute-Disable Bit Capability Not Enabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32
IA-32e Mode Page Level Protection Matrix with Execute-Disable Bit Capability Enabled . . . . . . . . . . . . . . . . . . . . . . . . 5-32
Protected-Mode Exceptions and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-2
Priority Among Simultaneous Exceptions and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-8
Debug Exception Conditions and Corresponding Exception Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21
Interrupt and Exception Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28
Conditions for Generating a Double Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28
Invalid TSS Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-31
Alignment Requirements by Data Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-45
SIMD Floating-Point Exceptions Priority. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-49
Exception Conditions Checked During a Task Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11
Effect of a Task Switch on Busy Flag, NT Flag, Previous Task Link Field, and TS Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13
Initial APIC IDs for the Logical Processors in a System that has Four Intel Xeon MP Processors Supporting Intel HyperThreading Technology1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-36
Initial APIC IDs for the Logical Processors in a System that has Two Physical Processors Supporting Dual-Core and Intel
Hyper-Threading Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-36
Example of Possible x2APIC ID Assignment in a System that has Two Physical Processors Supporting x2APIC and Intel
Hyper-Threading Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-37
Boot Phase IPI Message Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-53
IA-32 Processor States Following Power-up, Reset, or INIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-2
Recommended Settings of EM and MP Flags on IA-32 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-6
Software Emulation Settings of EM, MP, and NE Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-6
Main Initialization Steps in STARTUP.ASM Source Listing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15
Relationship Between BLD Item and ASM Source File. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-27
Microcode Update Field Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-28
Microcode Update Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-30
Extended Processor Signature Table Header Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-31
Processor Signature Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-31
Vol. 3A xxxiii
CONTENTS
PAGE
Table 9-10.
Table 9-11.
Table 9-12.
Table 9-13.
Table 9-14.
Table 9-15.
Table 9-16.
Table 9-17.
Table 9-18.
Table 10-1
Table 10-2.
Table 10-3
Table 10-4
Table 10-5.
Table 10-6.
Table 10-7.
Table 10-1.
Table 10-2.
Table 10-3.
Table 10-4.
Table 11-1.
Table 11-2.
Table 11-3.
Table 11-4.
Table 11-5.
Table 11-6.
Table 11-7.
Table 11-8.
Table 11-9.
Table 11-10.
Table 11-11.
Table 11-12.
Table 12-1.
Table 12-3.
Table 12-2.
Table 13-1.
Table 13-2.
Table 13-3.
Table 13-4.
Table 13-5.
Table 13-6.
Table 13-7.
Table 13-8.
Table 13-9.
Table 13-10.
Table 13-11.
Table 13-12.
Table 13-13.
Table 14-1.
Table 14-2.
Table 15-1.
Table 15-2.
Table 15-3.
Table 15-4.
Table 15-5.
Table 15-7.
Table 15-6.
Table 15-8.
xxxiv Vol. 3A
Processor Flags. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-33
Microcode Update Signature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-37
Microcode Update Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
Parameters for the Presence Test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
Parameters for the Write Update Data Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-43
Parameters for the Control Update Sub-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-47
Mnemonic Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-47
Parameters for the Read Microcode Update Data Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-47
Return Code Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-49
Local APIC Register Address Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-6
Local APIC Timer Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-17
Valid Combinations for the Pentium 4 and Intel Xeon Processors’
Local xAPIC Interrupt Command Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-21
Valid Combinations for the P6 Family Processors’
Local APIC Interrupt Command Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-22
x2APIC Operating Mode Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-37
Local APIC Register Address Map Supported by x2APIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-38
MSR/MMIO Interface of a Local x2APIC in Different Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-40
EOI Message (14 Cycles) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-47
Short Message (21 Cycles) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-48
Non-Focused Lowest Priority Message (34 Cycles) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-49
APIC Bus Status Cycles Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-51
Characteristics of the Caches, TLBs, Store Buffer, and
Write Combining Buffer in Intel 64 and IA-32 Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2
Memory Types and Their Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-6
Methods of Caching Available in Intel Core 2 Duo, Intel Atom, Intel Core Duo, Pentium M, Pentium 4, Intel Xeon, P6 Family,
and Pentium Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-7
MESI Cache Line States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-9
Cache Operating Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-12
Effective Page-Level Memory Type for Pentium Pro and Pentium II Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-14
Effective Page-Level Memory Types for Pentium III and More Recent Processor Families . . . . . . . . . . . . . . . . . . . . . .11-15
Memory Types That Can Be Encoded in MTRRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-21
Address Mapping for Fixed-Range MTRRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-24
Memory Types That Can Be Encoded With PAT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-34
Selection of PAT Entries with PAT, PCD, and PWT Flags. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-35
Memory Type Setting of PAT Entries Following a Power-up or Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-35
Action Taken By MMX Instructions for Different Combinations of EM, MP and TS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1
Effect of the MMX, x87 FPU, and FXSAVE/FXRSTOR Instructions on the x87 FPU Tag Word. . . . . . . . . . . . . . . . . . . . 12-3
Effects of MMX Instructions on x87 FPU State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3
Action Taken for Combinations of OSFXSR, OSXMMEXCPT, SSE, SSE2, SSE3, EM, MP, and TS1 . . . . . . . . . . . . . . . . . . 13-3
Action Taken for Combinations of OSFXSR, SSSE3, SSE4, EM, and TS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-3
XSAVE Header Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-9
XRSTOR Action on MXCSR, x87 FPU, XMM Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-10
XSAVE Action on MXCSR, x87 FPU, XMM Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-11
XCR0 and Processor State Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-14
CR4 bits for AVX New Instructions technology support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-14
Layout of XSAVE Area For Processor Supporting YMM State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-14
XSAVE Header Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-15
XSAVE Save Area Layout for YMM State (Ext_Save_Area_2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-15
XRSTOR Action on MXCSR, XMM Registers, YMM Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-15
Processor Supplied Init Values XRSTOR May Use. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-16
XSAVE Action on MXCSR, XMM, YMM Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-16
On-Demand Clock Modulation Duty Cycle Field Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-12
RAPL MSR Interfaces and RAPL Domains. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-21
Bits 54:53 in IA32_MCi_STATUS MSRs
when IA32_MCG_CAP[11] = 1 and UC = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-6
Overwrite Rules for Enabled Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-7
Address Mode in IA32_MCi_MISC[8:6]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-8
Extended Machine Check State MSRs
in Processors Without Support for Intel 64 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-9
Extended Machine Check State MSRs
In Processors With Support For Intel 64 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-10
Overwrite Rules for UC, CE, and UCR Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-16
MC Error Classifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-16
IA32_MCi_Status [15:0] Simple Error Code Encoding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15-18
CONTENTS
PAGE
Table 15-9.
Table 15-10.
Table 15-11.
Table 15-12.
Table 15-13.
Table 15-14.
Table 15-15.
Table 15-16.
Table 15-17.
Table 15-18.
Table 15-19.
Table 15-20.
Table 16-1.
Table 16-2.
Table 16-3.
Table 16-4.
Table 16-5.
Table 16-6.
Table 16-7.
Table 16-8.
Table 16-9.
Table 16-10.
Table 16-11.
Table 16-12.
Table 16-13.
Table 16-14.
Table 16-15.
Table 16-16.
Table 16-17.
Table 16-18.
Table 16-19.
Table 16-20.
Table 16-21.
Table 16-22.
Table 16-23.
Table 16-24.
Table 16-25.
Table 16-26.
Table 16-27.
Table 17-1.
Table 17-2.
Table 17-3.
Table 17-4.
Table 17-5.
Table 17-6.
Table 17-7.
Table 17-8.
Table 17-9.
Table 17-10.
Table 17-11.
Table 17-12.
Table 17-13.
Table 17-14.
Table 18-1.
Table 18-2.
Table 18-3.
Table 18-4.
Table 18-5.
Table 18-6.
Table 18-7.
Table 18-8.
Table 18-9.
Table 18-10.
Table 18-11.
IA32_MCi_Status [15:0] Compound Error Code Encoding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-19
Encoding for TT (Transaction Type) Sub-Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-20
Level Encoding for LL (Memory Hierarchy Level) Sub-Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-20
Encoding of Request (RRRR) Sub-Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-20
Encodings of PP, T, and II Sub-Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-21
Encodings of MMM and CCCC Sub-Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-21
MCA Compound Error Code Encoding for SRAO Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-22
IA32_MCi_STATUS Values for SRAO Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-22
IA32_MCG_STATUS Flag Indication for SRAO Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-22
MCA Compound Error Code Encoding for SRAR Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-23
IA32_MCi_STATUS Values for SRAR Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-23
IA32_MCG_STATUS Flag Indication for SRAR Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-23
CPUID DisplayFamily_DisplayModel Signatures for Processor Family 06H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-1
Incremental Decoding Information: Processor Family 06H Machine Error Codes For Machine Check. . . . . . . . . . . . . . 16-1
CPUID DisplayFamily_DisplayModel Signatures for Processors Based on Intel Core Microarchitecture . . . . . . . . . . . 16-3
Incremental Bus Error Codes of Machine Check for Processors
Based on Intel Core Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-4
Incremental MCA Error Code Types for Intel Xeon Processor 7400 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-6
Type B Bus and Interconnect Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-6
Type C Cache Bus Controller Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-7
Intel QPI Machine Check Error Codes for IA32_MC0_STATUS and IA32_MC1_STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8
Intel QPI Machine Check Error Codes for IA32_MC0_MISC and IA32_MC1_MISC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8
Machine Check Error Codes for IA32_MC7_STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8
Incremental Memory Controller Error Codes of Machine Check for IA32_MC8_STATUS . . . . . . . . . . . . . . . . . . . . . . . . . 16-9
Incremental Memory Controller Error Codes of Machine Check for IA32_MC8_MISC. . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-10
Machine Check Error Codes for IA32_MC4_STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-10
Intel QPI MC Error Codes for IA32_MC6_STATUS and IA32_MC7_STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-11
Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 8, 11) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-12
Intel IMC MC Error Codes for IA32_MCi_MISC (i= 8, 11). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-12
Machine Check Error Codes for IA32_MC4_STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-13
Intel IMC MC Error Codes for IA32-MCi_STATUS (i= 9, 16) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-15
Intel IMC MC Error Codes for IA32_MCi_MISC (i= 9, 16). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-15
Incremental Decoding Information: Processor Family 0FH Machine Error Codes For Machine Check . . . . . . . . . . . . . 16-16
MCi_STATUS Register Bit Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-17
Incremental MCA Error Code for Intel Xeon Processor MP 7100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-18
Other Information Field Bit Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-18
Type A: L3 Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-19
Type B Bus and Interconnect Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-19
Type C Cache Bus Controller Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-20
Decoding Family 0FH Machine Check Codes for Cache Hierarchy Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-21
Breakpoint Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-5
Debug Exception Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-7
LBR Stack Size and TOS Pointer Range. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-13
IA32_DEBUGCTL Flag Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-20
CPL-Qualified Branch Trace Store Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-21
IA32_LASTBRANCH_x_FROM_IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-24
IA32_LASTBRANCH_x_TO_IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-24
LBR Stack Size and TOS Pointer Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-24
MSR_LBR_SELECT for Intel microarchitecture code name Nehalem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-25
MSR_LBR_SELECT for Intel microarchitecture code name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-25
MSR_LBR_SELECT for Intel microarchitecture code name Haswell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-26
IA32_LASTBRANCH_x_FROM_IP with TSX Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-27
LBR MSR Stack Size and TOS Pointer Range for the Pentium® 4 and the Intel® Xeon® Processor Family . . . . . . . . . 17-29
Cache QoS Supported Event IDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-38
UMask and Event Select Encodings for Pre-Defined Architectural Performance Events . . . . . . . . . . . . . . . . . . . . . . . . . 18-9
Core Specificity Encoding within a Non-Architectural Umask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-11
Agent Specificity Encoding within a Non-Architectural Umask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-11
HW Prefetch Qualification Encoding within a Non-Architectural Umask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-12
MESI Qualification Definitions within a Non-Architectural Umask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-12
Bus Snoop Qualification Definitions within a Non-Architectural Umask. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-12
Snoop Type Qualification Definitions within a Non-Architectural Umask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-13
Association of Fixed-Function Performance Counters with Architectural Performance Events . . . . . . . . . . . . . . . . . 18-13
At-Retirement Performance Events for Intel Core Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-16
PEBS Performance Events for Intel Core Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-16
Requirements to Program PEBS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-18
Vol. 3A xxxv
CONTENTS
PAGE
Table 18-12.
Table 18-13.
Table 18-14.
Table 18-15.
Table 18-16.
Table 18-17.
Table 18-19.
Table 18-18.
Table 18-20.
Table 18-21.
Table 18-22.
Table 18-23.
Table 18-24.
Table 18-25.
Table 18-26.
Table 18-27.
Table 18-29.
Table 18-28.
Table 18-30.
Table 18-31.
Table 18-32.
Table 18-33.
Table 18-34.
Table 18-35.
Table 18-36.
Table 18-37.
Table 18-38.
Table 18-39.
Table 18-40.
Table 18-41.
Table 18-42.
Table 18-43.
Table 19-1.
Table 19-2.
Table 19-3.
Table 19-4.
Table 19-5.
Table 19-6.
Table 19-7.
Table 19-8.
Table 19-9.
Table 19-10.
Table 19-11.
Table 19-12.
Table 19-13.
Table 19-14.
Table 19-15.
Table 19-16.
Table 19-17.
Table 19-18.
Table 19-19.
xxxvi Vol. 3A
PEBS Record Format for Intel Core i7 Processor Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-22
Data Source Encoding for Load Latency Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-25
Off-Core Response Event Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-26
MSR_OFFCORE_RSP_0 and MSR_OFFCORE_RSP_1 Bit Field Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-28
Opcode Field Encoding for MSR_UNCORE_ADDR_OPCODE_MATCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-33
Uncore PMU MSR Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-34
Core PMU Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-36
Uncore PMU MSR Summary for Intel® Xeon® Processor E7 Family. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-36
PEBS Facility Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-39
PEBS Performance Events for Intel® Microarchitecture Code Name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-40
Layout of Data Source Field of Load Latency Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-42
Layout of Precise Store Information In PEBS Record. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-43
Off-Core Response Event Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-43
MSR_OFFCORE_RSP_x Request_Type Field Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-44
MSR_OFFCORE_RSP_x Response Supplier Info Field Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-45
MSR_OFFCORE_RSP_x Snoop Info Field Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-46
MSR_OFFCORE_RSP_x Supplier Info Field Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-48
Uncore PMU MSR Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-48
Uncore PMU MSR Summary for Intel® Xeon® Processor E5 Family. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-49
Core PMU Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-49
PEBS Facility Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-50
PEBS Record Format for Next Generation Intel Core Processor Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-51
Precise Events That Supports Data Linear Address Profiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-51
Layout of Data Linear Address Information In PEBS Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-52
MSR_OFFCORE_RSP_x Request_Type Definition (Haswell). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-53
TX Abort Information Field Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-55
Uncore PMU MSR Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-55
Performance Counter MSRs and Associated CCCR and
ESCR MSRs (Pentium 4 and Intel Xeon Processors) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-56
Event Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-63
CCR Names and Bit Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-67
Effect of Logical Processor and CPL Qualification
for Logical-Processor-Specific (TS) Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-76
Effect of Logical Processor and CPL Qualification
for Non-logical-Processor-specific (TI) Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-77
Architectural Performance Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1
Non-Architectural Performance Events In the Processor Core of
Next Generation Intel® Core™ Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-2
Intel TSX Performance Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-10
Non-Architectural Uncore Performance Events In the Next Generation Intel® Core™ Processors . . . . . . . . . . . . . . . .19-12
Non-Architectural Performance Events In the Processor Core of
3rd Generation Intel® Core™ i7, i5, i3 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-13
Non-Architectural Performance Events Applicable only to the Processor Core of
Next Generation Intel® Xeon® Processor E5 Family. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-22
Non-Architectural Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E5 Family. . . . . . . . . . . . . . . . . . .19-22
Non-Architectural Performance Events applicable only to the Processor core for 2nd Generation Intel® Core™ i7-2xxx,
Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-31
Non-Architectural Performance Events Applicable only to the Processor Core of
Intel® Xeon® Processor E5 Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-33
Non-Architectural Performance Events In the Processor Uncore for 2nd Generation
Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-35
Non-Architectural Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-36
Non-Architectural Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-53
Non-Architectural Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-65
Non-Architectural Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-82
Non-Architectural Performance Events for Processors Based on Enhanced Intel Core Microarchitecture . . . . . . . .19-97
Fixed-Function Performance Counter and Pre-defined Performance Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-97
Non-Architectural Performance Events in Processors Based on Intel® Core™ Microarchitecture . . . . . . . . . . . . . . . . .19-98
Non-Architectural Performance Events for Intel® Atom™ Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-123
Non-Architectural Performance Events in Intel® Core™ Solo and Intel® Core™ Duo Processors . . . . . . . . . . . . . . . . . 19-137
CONTENTS
PAGE
Table 19-20.
Table 19-21.
Table 19-22.
Table 19-23.
Table 19-24.
Table 19-25.
Table 19-26.
Table 19-27.
Table 19-28.
Table 19-29.
Table 19-30.
Table 20-1.
Table 20-2.
Table 21-1.
Table 22-1.
Table 22-3.
Table 22-2.
Table 22-4.
Table 22-5.
Table 22-6.
Table 22-7.
Table 22-8.
Table 22-9.
Table 24-1.
Table 24-2.
Table 24-3.
Table 24-4.
Table 24-5.
Table 24-6.
Table 24-7.
Table 24-8.
Table 24-9.
Table 24-10.
Table 24-11.
Table 24-12.
Table 24-13.
Table 24-14.
Table 24-15.
Table 24-16.
Table 24-17.
Table 25-1.
Table 27-1.
Table 27-2.
Table 27-3.
Table 27-5.
Table 27-4.
Table 27-6.
Table 27-7.
Table 27-9.
Table 27-8.
Table 27-10.
Table 27-11.
Table 27-13.
Table 27-12.
Table 27-14.
Table 28-1.
Table 28-2.
Table 28-3.
Table 28-4.
Table 28-5.
Table 28-6.
Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-142
Performance Monitoring Events For Intel NetBurst® Microarchitecture
for At-Retirement Counting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-160
Intel NetBurst® Microarchitecture Model-Specific Performance Monitoring Events
(For Model Encoding 3, 4 or 6). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-165
List of Metrics Available for Front_end Tagging (For Front_end Event Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-165
List of Metrics Available for Execution Tagging (For Execution Event Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-165
List of Metrics Available for Replay Tagging (For Replay Event Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-166
Event Mask Qualification for Logical Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-167
Performance Monitoring Events on Intel® Pentium® M Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-172
Performance Monitoring Events Modified on Intel® Pentium® M Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-173
Events That Can Be Counted with the P6 Family Performance-Monitoring Counters. . . . . . . . . . . . . . . . . . . . . . . . . .19-174
Events That Can Be Counted with Pentium Processor Performance-Monitoring Counters. . . . . . . . . . . . . . . . . . . . .19-183
Real-Address Mode Exceptions and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-6
Software Interrupt Handling Methods While in Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-17
Characteristics of 16-Bit and 32-Bit Program Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-1
New Instruction in the Pentium Processor and Later IA-32 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4
EM and MP Flag Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-16
Recommended Values of the EM, MP, and NE Flags for Intel486 SX Microprocessor/Intel 487 SX Math Coprocessor
System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-16
Exception Conditions for Legacy SIMD/MMX Instructions with FP Exception and 16-Byte Alignment . . . . . . . . . . . 22-21
Exception Conditions for Legacy SIMD/MMX Instructions with XMM and FP Exception . . . . . . . . . . . . . . . . . . . . . . . . . 22-22
Exception Conditions for Legacy SIMD/MMX Instructions with XMM and without FP Exception. . . . . . . . . . . . . . . . . 22-23
Exception Conditions for SIMD/MMX Instructions with Memory Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-24
Exception Conditions for Legacy SIMD/MMX Instructions without FP Exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-25
Exception Conditions for Legacy SIMD/MMX Instructions without Memory Reference . . . . . . . . . . . . . . . . . . . . . . . . . 22-26
Format of the VMCS Region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-2
Format of Access Rights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-4
Format of Interruptibility State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-6
Format of Pending-Debug-Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-7
Definitions of Pin-Based VM-Execution Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-8
Definitions of Primary Processor-Based VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-9
Definitions of Secondary Processor-Based VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-10
Format of Extended-Page-Table Pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-14
Definitions of VM-Function Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-15
Definitions of VM-Exit Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-16
Format of an MSR Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-17
Definitions of VM-Entry Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-17
Format of the VM-Entry Interruption-Information Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-18
Format of Exit Reason . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-19
Format of the VM-Exit Interruption-Information Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-20
Format of the IDT-Vectoring Information Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-21
Structure of VMCS Component Encoding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-23
Format of the Virtualization-Exception Information Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-15
Exit Qualification for Debug Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-4
Exit Qualification for Task Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-5
Exit Qualification for Control-Register Accesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-6
Exit Qualification for I/O Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-7
Exit Qualification for MOV DR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-7
Exit Qualification for APIC-Access VM Exits from Linear Accesses and Guest-Physical Accesses. . . . . . . . . . . . . . . . . 27-8
Exit Qualification for EPT Violations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-9
Format of the VM-Exit Instruction-Information Field as Used for INVEPT, INVPCID, and INVVPID . . . . . . . . . . . . . . . 27-14
Format of the VM-Exit Instruction-Information Field as Used for INS and OUTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-14
Format of the VM-Exit Instruction-Information Field as Used for LIDT, LGDT, SIDT, or SGDT. . . . . . . . . . . . . . . . . . . . 27-15
Format of the VM-Exit Instruction-Information Field as Used for LLDT, LTR, SLDT, and STR. . . . . . . . . . . . . . . . . . . . 27-16
Format of the VM-Exit Instruction-Information Field as Used for VMCLEAR, VMPTRLD, VMPTRST, and VMXON . 27-18
Format of the VM-Exit Instruction-Information Field as Used for RDRAND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-18
Format of the VM-Exit Instruction-Information Field as Used for VMREAD and VMWRITE . . . . . . . . . . . . . . . . . . . . . . 27-19
Format of an EPT PML4 Entry (PML4E) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-3
Format of an EPT Page-Directory-Pointer-Table Entry (PDPTE) that Maps a 1-GByte Page . . . . . . . . . . . . . . . . . . . . . 28-4
Format of an EPT Page-Directory-Pointer-Table Entry (PDPTE) that References an EPT Page Directory . . . . . . . . . 28-5
Format of an EPT Page-Directory Entry (PDE) that Maps a 2-MByte Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-6
Format of an EPT Page-Directory Entry (PDE) that References an EPT Page Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-7
Format of an EPT Page-Table Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-8
Vol. 3A xxxvii
CONTENTS
PAGE
Table 29-1.
Table 30-1.
Table 31-1.
Table 34-1.
Table 34-2.
Table 34-3.
Table 34-4.
Table 34-5.
Table 34-6.
Table 34-7.
Table 34-8.
Table 34-9.
Table 34-10.
Table 35-1.
Table 35-2.
Table 35-3.
Table 35-4.
Table 35-5.
Table 35-6.
Table 35-7.
Table 35-8.
Table 35-9.
Table 35-10.
Table 35-11.
Table 35-12.
Table 35-13.
Table 35-14.
Table 35-15.
Table 35-16.
Table 35-17.
Table 35-18.
Table 35-19.
Table 35-20.
Table 35-21.
Table 35-22.
Table 35-23.
Table 35-24.
Table A-1.
Table B-1.
Table B-2.
Table B-3.
Table B-4.
Table B-5.
Table B-6.
Table B-7.
Table B-8.
Table B-9.
Table B-10.
Table B-11.
Table B-12.
Table B-13.
Table B-14.
Table B-15.
Table C-1.
xxxviii Vol. 3A
Format of Posted-Interrupt Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29-13
VM-Instruction Error Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30-31
Operating Modes for Host and Guest Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-12
SMRAM State Save Map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-5
Processor Signatures and 64-bit SMRAM State Save Map Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-6
SMRAM State Save Map for Intel 64 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-7
Processor Register Initialization in SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-9
I/O Instruction Information in the SMM State Save Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-12
I/O Instruction Type Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-12
Auto HALT Restart Flag Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-14
I/O Instruction Restart Field Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-15
Exit Qualification for SMIs That Arrive Immediately After the Retirement of an I/O Instruction . . . . . . . . . . . . . . . . .34-20
Format of MSEG Header. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-25
CPUID Signature Values of DisplayFamily_DisplayModel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-1
IA-32 Architectural MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-2
MSRs in Processors Based on Intel® Core™ Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-28
MSRs in Intel® Atom™ Processor Family. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-42
MSRs Supported by Intel® Atom™ Processors with CPUID Signature 06_27H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-53
MSRs in Processors Based on Intel® Microarchitecture Code Name Nehalem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-54
Additional MSRs in Intel® Xeon® Processor 5500 and 3400 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-70
Additional MSRs in Intel® Xeon® Processor 7500 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-71
Additional MSRs Supported by Intel Processors
(Based on Intel® Microarchitecture Code Name Westmere) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-86
Additional MSRs Supported by Intel® Xeon® Processor E7 Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-87
MSRs Supported by Intel® Processors
Based on Intel® Microarchitecture Code Name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-88
MSRs Supported by Second Generation Intel® Core™ Processors (Intel® Microarchitecture Code Name Sandy Bridge). . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-104
Selected MSRs Supported by Intel® Xeon® Processors E5 Family (Based on Intel® Microarchitecture Code Name Sandy
Bridge) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-107
Additional MSRs Supported by 3rd Generation Intel® Core™ Processors (Based on Intel® Microarchitecture Code Name Ivy
Bridge) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-110
Selected MSRs Supported by Intel® Xeon® Processors E5 Family v2 (Based on Intel® Microarchitecture Code Name Ivy
Bridge) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-112
Additional MSRs Supported by Next Generation Intel® Core™ Processors (Based on Intel® Microarchitecture Code Name
Haswell) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-115
Additional MSRs Supported by Future Generation Intel® Xeon® Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-116
MSRs in the Pentium® 4 and Intel® Xeon® Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-117
MSRs Unique to 64-bit Intel® Xeon® Processor MP with
Up to an 8 MB L3 Cache. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-141
MSRs Unique to Intel Xeon Processor 7100 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-142
MSRs in Intel® Core™ Solo, Intel® Core™ Duo Processors, and Dual-Core Intel® Xeon® Processor LV . . . . . . . . . . . . . 35-143
MSRs in Pentium M Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-152
MSRs in the P6 Family Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-159
MSRs in the Pentium Processor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-167
Memory Types Used For VMCS Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1
Encoding for 16-Bit Control Fields (0000_00xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1
Encodings for 16-Bit Guest-State Fields (0000_10xx_xxxx_xxx0B). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1
Encodings for 16-Bit Host-State Fields (0000_11xx_xxxx_xxx0B). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2
Encodings for 64-Bit Control Fields (0010_00xx_xxxx_xxxAb) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2
Encodings for 64-Bit Read-Only Data Field (0010_01xx_xxxx_xxxAb) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4
Encodings for 64-Bit Guest-State Fields (0010_10xx_xxxx_xxxAb). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4
Encodings for 64-Bit Host-State Fields (0010_11xx_xxxx_xxxAb). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-5
Encodings for 32-Bit Control Fields (0100_00xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-5
Encodings for 32-Bit Read-Only Data Fields (0100_01xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-6
Encodings for 32-Bit Guest-State Fields
(0100_10xx_xxxx_xxx0B)B-6
Encoding for 32-Bit Host-State Field (0100_11xx_xxxx_xxx0B). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-7
Encodings for Natural-Width Control Fields (0110_00xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-8
Encodings for Natural-Width Read-Only Data Fields (0110_01xx_xxxx_xxx0B). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-8
Encodings for Natural-Width Guest-State Fields (0110_10xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-8
Encodings for Natural-Width Host-State Fields (0110_11xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-9
Basic Exit Reasons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .C-1
CHAPTER 1
ABOUT THIS MANUAL
The Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A: System Programming Guide,
Part 1 (order number 253668), the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3B:
System Programming Guide, Part 2 (order number 253669) and the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 3C: System Programming Guide, Part 3 (order number 326019) are part of a set that
describes the architecture and programming environment of Intel 64 and IA-32 Architecture processors. The other
volumes in this set are:
•
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1: Basic Architecture (order number
253665).
•
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes 2A, 2B & 2C: Instruction Set
Reference (order numbers 253666, 253667 and 326018).
The Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, describes the basic architecture
and programming environment of Intel 64 and IA-32 processors. The Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volumes 2A, 2B & 2C, describe the instruction set of the processor and the opcode structure.
These volumes apply to application programmers and to programmers who write operating systems or executives.
The Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes 3A, 3B & 3C, describe the operating-system support environment of Intel 64 and IA-32 processors. These volumes target operating-system and
BIOS designers. In addition, Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3B, and
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3C address the programming environment for classes of software that host operating systems.
1.1
INTEL® 64 AND IA-32 PROCESSORS COVERED IN THIS MANUAL
This manual set includes information pertaining primarily to the most recent Intel 64 and IA-32 processors, which
include:
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Pentium® processors
P6 family processors
Pentium® 4 processors
Pentium® M processors
Intel® Xeon® processors
Pentium® D processors
Pentium® processor Extreme Editions
64-bit Intel® Xeon® processors
Intel® Core™ Duo processor
Intel® Core™ Solo processor
Dual-Core Intel® Xeon® processor LV
Intel® Core™2 Duo processor
Intel® Core™2 Quad processor Q6000 series
Intel® Xeon® processor 3000, 3200 series
Intel® Xeon® processor 5000 series
Intel® Xeon® processor 5100, 5300 series
Intel® Core™2 Extreme processor X7000 and X6800 series
Intel® Core™2 Extreme QX6000 series
Intel® Xeon® processor 7100 series
Vol. 3A 1-1
ABOUT THIS MANUAL
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Intel® Pentium® Dual-Core processor
Intel® Xeon® processor 7200, 7300 series
Intel® Core™2 Extreme QX9000 series
Intel® Xeon® processor 5200, 5400, 7400 series
Intel® CoreTM2 Extreme processor QX9000 and X9000 series
Intel® CoreTM2 Quad processor Q9000 series
Intel® CoreTM2 Duo processor E8000, T9000 series
Intel® AtomTM processor family
Intel® CoreTM i7 processor
Intel® CoreTM i5 processor
Intel® Xeon® processor E7-8800/4800/2800 product families
Intel® Xeon® processor E5 family
Intel® Xeon® processor E3-1200 family
Intel® CoreTM i7-3930K processor
2nd generation Intel® CoreTM i7-2xxx, Intel® CoreTM i5-2xxx, Intel® CoreTM i3-2xxx processor series
Intel® Xeon® processor E3-1200 v2 product family
3rd generation Intel® CoreTM processors
Next generation Intel® CoreTM processors
P6 family processors are IA-32 processors based on the P6 family microarchitecture. This includes the Pentium®
Pro, Pentium® II, Pentium® III, and Pentium® III Xeon® processors.
The Pentium® 4, Pentium® D, and Pentium® processor Extreme Editions are based on the Intel NetBurst® microarchitecture. Most early Intel® Xeon® processors are based on the Intel NetBurst® microarchitecture. Intel Xeon
processor 5000, 7100 series are based on the Intel NetBurst® microarchitecture.
The Intel® Core™ Duo, Intel® Core™ Solo and dual-core Intel® Xeon® processor LV are based on an improved
Pentium® M processor microarchitecture.
The Intel® Xeon® processor 3000, 3200, 5100, 5300, 7200, and 7300 series, Intel® Pentium® dual-core, Intel®
Core™2 Duo, Intel® Core™2 Quad and Intel® Core™2 Extreme processors are based on Intel® Core™ microarchitecture.
The Intel® Xeon® processor 5200, 5400, 7400 series, Intel® CoreTM2 Quad processor Q9000 series, and Intel®
CoreTM2 Extreme processors QX9000, X9000 series, Intel® CoreTM2 processor E8000 series are based on Enhanced
Intel® CoreTM microarchitecture.
The Intel® AtomTM processor family is based on the Intel® AtomTM microarchitecture and supports Intel 64 architecture.
The Intel® CoreTM i7 processor and the Intel® CoreTM i5 processor are based on the Intel® microarchitecture code
name Nehalem and support Intel 64 architecture.
Processors based on Intel® microarchitecture code name Westmere support Intel 64 architecture.
The Intel® Xeon® processor E5 family, Intel® Xeon® processor E3-1200 family, Intel® Xeon® processor E78800/4800/2800 product families, Intel® CoreTM i7-3930K processor, 2nd generation Intel® CoreTM i7-2xxx, Intel®
CoreTM i5-2xxx, Intel® CoreTM i3-2xxx processor series are based on the Intel® microarchitecture code name Sandy
Bridge and support Intel 64 architecture.
The Intel® Xeon® processor E3-1200 v2 product family and 3rd generation Intel® CoreTM processors are based on
the Intel® microarchitecture code name Ivy Bridge and support Intel 64 architecture.
The Next Generation Intel® CoreTM processors are based on the Intel® microarchitecture code name Haswell and
support Intel 64 architecture.
P6 family, Pentium® M, Intel® Core™ Solo, Intel® Core™ Duo processors, dual-core Intel® Xeon® processor LV,
and early generations of Pentium 4 and Intel Xeon processors support IA-32 architecture. The Intel® Atom™
processor Z5xx series support IA-32 architecture.
1-2 Vol. 3A
ABOUT THIS MANUAL
The Intel® Xeon® processor 3000, 3200, 5000, 5100, 5200, 5300, 5400, 7100, 7200, 7300, 7400 series, Intel®
Core™2 Duo, Intel® Core™2 Extreme processors, Intel Core 2 Quad processors, Pentium® D processors, Pentium®
Dual-Core processor, newer generations of Pentium 4 and Intel Xeon processor family support Intel® 64 architecture.
IA-32 architecture is the instruction set architecture and programming environment for Intel's 32-bit microprocessors. Intel® 64 architecture is the instruction set architecture and programming environment which is a superset
of and compatible with IA-32 architecture.
1.2
OVERVIEW OF THE SYSTEM PROGRAMMING GUIDE
A description of this manual’s content follows:
Chapter 1 — About This Manual. Gives an overview of all seven volumes of the Intel® 64 and IA-32 Architectures Software Developer’s Manual. It also describes the notational conventions in these manuals and lists related
Intel manuals and documentation of interest to programmers and hardware designers.
Chapter 2 — System Architecture Overview. Describes the modes of operation used by Intel 64 and IA-32
processors and the mechanisms provided by the architectures to support operating systems and executives,
including the system-oriented registers and data structures and the system-oriented instructions. The steps
necessary for switching between real-address and protected modes are also identified.
Chapter 3 — Protected-Mode Memory Management. Describes the data structures, registers, and instructions
that support segmentation and paging. The chapter explains how they can be used to implement a “flat” (unsegmented) memory model or a segmented memory model.
Chapter 4 — Paging. Describes the paging modes supported by Intel 64 and IA-32 processors.
Chapter 5 — Protection. Describes the support for page and segment protection provided in the Intel 64 and IA32 architectures. This chapter also explains the implementation of privilege rules, stack switching, pointer validation, user and supervisor modes.
Chapter 6 — Interrupt and Exception Handling. Describes the basic interrupt mechanisms defined in the Intel
64 and IA-32 architectures, shows how interrupts and exceptions relate to protection, and describes how the architecture handles each exception type. Reference information for each exception is given in this chapter. Includes
programming the LINT0 and LINT1 inputs and gives an example of how to program the LINT0 and LINT1 pins for
specific interrupt vectors.
Chapter 7 — Task Management. Describes mechanisms the Intel 64 and IA-32 architectures provide to support
multitasking and inter-task protection.
Chapter 8 — Multiple-Processor Management. Describes the instructions and flags that support multiple
processors with shared memory, memory ordering, and Intel® Hyper-Threading Technology. Includes MP initialization for P6 family processors and gives an example of how to use of the MP protocol to boot P6 family processors in
an MP system.
Chapter 9 — Processor Management and Initialization. Defines the state of an Intel 64 or IA-32 processor
after reset initialization. This chapter also explains how to set up an Intel 64 or IA-32 processor for real-address
mode operation and protected- mode operation, and how to switch between modes.
Chapter 10 — Advanced Programmable Interrupt Controller (APIC). Describes the programming interface
to the local APIC and gives an overview of the interface between the local APIC and the I/O APIC. Includes APIC bus
message formats and describes the message formats for messages transmitted on the APIC bus for P6 family and
Pentium processors.
Chapter 11 — Memory Cache Control. Describes the general concept of caching and the caching mechanisms
supported by the Intel 64 or IA-32 architectures. This chapter also describes the memory type range registers
(MTRRs) and how they can be used to map memory types of physical memory. Information on using the new cache
control and memory streaming instructions introduced with the Pentium III, Pentium 4, and Intel Xeon processors
is also given.
Chapter 12 — Intel® MMX™ Technology System Programming. Describes those aspects of the Intel® MMX™
technology that must be handled and considered at the system programming level, including: task switching,
exception handling, and compatibility with existing system environments.
Vol. 3A 1-3
ABOUT THIS MANUAL
Chapter 13 — System Programming For Instruction Set Extensions And Processor Extended States.
Describes the operating system requirements to support SSE/SSE2/SSE3/SSSE3/SSE4 extensions, including task
switching, exception handling, and compatibility with existing system environments. The latter part of this chapter
describes the extensible framework of operating system requirements to support processor extended states.
Processor extended state may be required by instruction set extensions beyond those of
SSE/SSE2/SSE3/SSSE3/SSE4 extensions.
Chapter 14 — Power and Thermal Management. Describes facilities of Intel 64 and IA-32 architecture used for
power management and thermal monitoring.
Chapter 15 — Machine-Check Architecture. Describes the machine-check architecture and machinecheck exception mechanism found in the Pentium 4, Intel Xeon, and P6 family processors. Additionally,
a signaling mechanism for software to respond to hardware corrected machine check error is covered.
Chapter 16 — Interpreting Machine-Check Error Codes. Gives an example of how to interpret the error codes
for a machine-check error that occurred on a P6 family processor.
Chapter 17 — Debugging, Branch Profiles and Time-Stamp Counter. Describes the debugging registers and
other debug mechanism provided in Intel 64 or IA-32 processors. This chapter also describes the time-stamp
counter.
Chapter 18 — Performance Monitoring. Describes the Intel 64 and IA-32 architectures’ facilities for monitoring
performance.
Chapter 19 — Performance-Monitoring Events. Lists architectural performance events. Non-architectural
performance events (i.e. model-specific events) are listed for each generation of microarchitecture.
Chapter 20 — 8086 Emulation. Describes the real-address and virtual-8086 modes of the IA-32 architecture.
Chapter 21 — Mixing 16-Bit and 32-Bit Code. Describes how to mix 16-bit and 32-bit code modules within the
same program or task.
Chapter 22 — IA-32 Architecture Compatibility. Describes architectural compatibility among IA-32 processors.
Chapter 23 — Introduction to Virtual-Machine Extensions. Describes the basic elements of virtual machine
architecture and the virtual-machine extensions for Intel 64 and IA-32 Architectures.
Chapter 24 — Virtual-Machine Control Structures. Describes components that manage VMX operation. These
include the working-VMCS pointer and the controlling-VMCS pointer.
Chapter 25 — VMX Non-Root Operation. Describes the operation of a VMX non-root operation. Processor operation in VMX non-root mode can be restricted programmatically such that certain operations, events or conditions
can cause the processor to transfer control from the guest (running in VMX non-root mode) to the monitor software
(running in VMX root mode).
Chapter 26 — VM Entries. Describes VM entries. VM entry transitions the processor from the VMM running in VMX
root-mode to a VM running in VMX non-root mode. VM-Entry is performed by the execution of VMLAUNCH or VMRESUME instructions.
Chapter 27 — VM Exits. Describes VM exits. Certain events, operations or situations while the processor is in VMX
non-root operation may cause VM-exit transitions. In addition, VM exits can also occur on failed VM entries.
Chapter 28 — VMX Support for Address Translation. Describes virtual-machine extensions that support
address translation and the virtualization of physical memory.
Chapter 29 — APIC Virtualization and Virtual Interrupts. Describes the VMCS including controls that enable
the virtualization of interrupts and the Advanced Programmable Interrupt Controller (APIC).
Chapter 30 — VMX Instruction Reference. Describes the virtual-machine extensions (VMX). VMX is intended
for a system executive to support virtualization of processor hardware and a system software layer acting as a host
to multiple guest software environments.
Chapter 31 — Virtual-Machine Monitoring Programming Considerations. Describes programming considerations for VMMs. VMMs manage virtual machines (VMs).
Chapter 32 — Virtualization of System Resources. Describes the virtualization of the system resources. These
include: debugging facilities, address translation, physical memory, and microcode update facilities.
1-4 Vol. 3A
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Chapter 33 — Handling Boundary Conditions in a Virtual Machine Monitor. Describes what a VMM must
consider when handling exceptions, interrupts, error conditions, and transitions between activity states.
Chapter 34 — System Management Mode. Describes Intel 64 and IA-32 architectures’ system management
mode (SMM) facilities.
Chapter 35 — Model-Specific Registers (MSRs). Lists the MSRs available in the Pentium processors, the P6
family processors, the Pentium 4, Intel Xeon, Intel Core Solo, Intel Core Duo processors, and Intel Core 2
processor family and describes their functions.
Appendix A — VMX Capability Reporting Facility. Describes the VMX capability MSRs. Support for specific VMX
features is determined by reading capability MSRs.
Appendix B — Field Encoding in VMCS. Enumerates all fields in the VMCS and their encodings. Fields are
grouped by width (16-bit, 32-bit, etc.) and type (guest-state, host-state, etc.).
Appendix C — VM Basic Exit Reasons. Describes the 32-bit fields that encode reasons for a VM exit. Examples
of exit reasons include, but are not limited to: software interrupts, processor exceptions, software traps, NMIs,
external interrupts, and triple faults.
1.3
NOTATIONAL CONVENTIONS
This manual uses specific notation for data-structure formats, for symbolic representation of instructions, and for
hexadecimal and binary numbers. A review of this notation makes the manual easier to read.
1.3.1
Bit and Byte Order
In illustrations of data structures in memory, smaller addresses appear toward the bottom of the figure; addresses
increase toward the top. Bit positions are numbered from right to left. The numerical value of a set bit is equal to
two raised to the power of the bit position. Intel 64 and IA-32 processors are “little endian” machines; this means
the bytes of a word are numbered starting from the least significant byte. Figure 1-1 illustrates these conventions.
1.3.2
Reserved Bits and Software Compatibility
In many register and memory layout descriptions, certain bits are marked as reserved. When bits are marked as
reserved, it is essential for compatibility with future processors that software treat these bits as having a future,
though unknown, effect. The behavior of reserved bits should be regarded as not only undefined, but unpredictable. Software should follow these guidelines in dealing with reserved bits:
•
Do not depend on the states of any reserved bits when testing the values of registers which contain such bits.
Mask out the reserved bits before testing.
•
•
•
Do not depend on the states of any reserved bits when storing to memory or to a register.
Do not depend on the ability to retain information written into any reserved bits.
When loading a register, always load the reserved bits with the values indicated in the documentation, if any,
or reload them with values previously read from the same register.
NOTE
Avoid any software dependence upon the state of reserved bits in Intel 64 and IA-32 registers.
Depending upon the values of reserved register bits will make software dependent upon the
unspecified manner in which the processor handles these bits. Programs that depend upon
reserved values risk incompatibility with future processors.
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Highest
31
Address
Data Structure
8 7
24 23
16 15
Byte 3
Byte 2
Byte 1
Bit offset
0
Byte 0
28
24
20
16
12
8
4
0
Lowest
Address
Byte Offset
Figure 1-1. Bit and Byte Order
1.3.3
Instruction Operands
When instructions are represented symbolically, a subset of assembly language is used. In this subset, an instruction has the following format:
label: mnemonic argument1, argument2, argument3
where:
•
•
•
A label is an identifier which is followed by a colon.
A mnemonic is a reserved name for a class of instruction opcodes which have the same function.
The operands argument1, argument2, and argument3 are optional. There may be from zero to three
operands, depending on the opcode. When present, they take the form of either literals or identifiers for data
items. Operand identifiers are either reserved names of registers or are assumed to be assigned to data items
declared in another part of the program (which may not be shown in the example).
When two operands are present in an arithmetic or logical instruction, the right operand is the source and the left
operand is the destination.
For example:
LOADREG: MOV EAX, SUBTOTAL
In this example LOADREG is a label, MOV is the mnemonic identifier of an opcode, EAX is the destination operand,
and SUBTOTAL is the source operand. Some assembly languages put the source and destination in reverse order.
1.3.4
Hexadecimal and Binary Numbers
Base 16 (hexadecimal) numbers are represented by a string of hexadecimal digits followed by the character H (for
example, F82EH). A hexadecimal digit is a character from the following set: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D,
E, and F.
Base 2 (binary) numbers are represented by a string of 1s and 0s, sometimes followed by the character B (for
example, 1010B). The “B” designation is only used in situations where confusion as to the type of number might
arise.
1.3.5
Segmented Addressing
The processor uses byte addressing. This means memory is organized and accessed as a sequence of bytes.
Whether one or more bytes are being accessed, a byte address is used to locate the byte or bytes memory. The
range of memory that can be addressed is called an address space.
1-6 Vol. 3A
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The processor also supports segmented addressing. This is a form of addressing where a program may have many
independent address spaces, called segments. For example, a program can keep its code (instructions) and stack
in separate segments. Code addresses would always refer to the code space, and stack addresses would always
refer to the stack space. The following notation is used to specify a byte address within a segment:
Segment-register:Byte-address
For example, the following segment address identifies the byte at address FF79H in the segment pointed by the DS
register:
DS:FF79H
The following segment address identifies an instruction address in the code segment. The CS register points to the
code segment and the EIP register contains the address of the instruction.
CS:EIP
1.3.6
Syntax for CPUID, CR, and MSR Values
Obtain feature flags, status, and system information by using the CPUID instruction, by checking control register
bits, and by reading model-specific registers. We are moving toward a single syntax to represent this type of information. See Figure 1-2.
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Figure 1-2. Syntax for CPUID, CR, and MSR Data Presentation
Vol. 3A 1-7
ABOUT THIS MANUAL
1.3.7
Exceptions
An exception is an event that typically occurs when an instruction causes an error. For example, an attempt to
divide by zero generates an exception. However, some exceptions, such as breakpoints, occur under other conditions. Some types of exceptions may provide error codes. An error code reports additional information about the
error. An example of the notation used to show an exception and error code is shown below:
#PF(fault code)
This example refers to a page-fault exception under conditions where an error code naming a type of fault is
reported. Under some conditions, exceptions which produce error codes may not be able to report an accurate
code. In this case, the error code is zero, as shown below for a general-protection exception:
#GP(0)
1.4
RELATED LITERATURE
Literature related to Intel 64 and IA-32 processors is listed on-line at:
http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html.html
Some of the documents listed at this web site can be viewed on-line; others can be ordered. The literature available
is listed by Intel processor and then by the following literature types: applications notes, data sheets, manuals,
papers, and specification updates.
See also:
•
•
•
The data sheet for a particular Intel 64 or IA-32 processor
•
Intel® Fortran Compiler documentation and online help:
http://software.intel.com/en-us/articles/intel-compilers/
•
Intel® VTune™ Performance Analyzer documentation and online help:
http://www.intel.com/cd/software/products/asmo-na/eng/index.htm
•
Intel® 64 and IA-32 Architectures Software Developer’s Manual (in three or five volumes):
http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html.html
•
Intel® 64 and IA-32 Architectures Optimization Reference Manual:
http://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-optimizationmanual.html
•
Intel® Processor Identification with the CPUID Instruction, AP-485:
http://www.intel.com/Assets/PDF/appnote/241618.pdf
•
Intel 64 Architecture x2APIC Specification:
The specification update for a particular Intel 64 or IA-32 processor
Intel® C++ Compiler documentation and online help:
http://software.intel.com/en-us/articles/intel-compilers/
http://www.intel.com/content/www/us/en/architecture-and-technology/64-architecture-x2apic-specification.html
•
Intel 64 Architecture Processor Topology Enumeration:
http://softwarecommunity.intel.com/articles/eng/3887.htm
•
Intel® Trusted Execution Technology Measured Launched Environment Programming Guide:
http://www.intel.com/content/www/us/en/software-developers/intel-txt-software-development-guide.html
•
Intel® SSE4 Programming Reference: http://edc.intel.com/Link.aspx?id=1630&wapkw=intel® sse4
programming reference
•
Developing Multi-threaded Applications: A Platform Consistent Approach:
http://cache-www.intel.com/cd/00/00/05/15/51534_developing_multithreaded_applications.pdf
1-8 Vol. 3A
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•
Using Spin-Loops on Intel® Pentium® 4 Processor and Intel® Xeon® Processor:
http://software.intel.com/en-us/articles/ap949-using-spin-loops-on-intel-pentiumr-4-processor-and-intelxeonr-processor/
•
Performance Monitoring Unit Sharing Guide
http://software.intel.com/file/30388
More relevant links are:
•
Software network link:
http://softwarecommunity.intel.com/isn/home/
•
Developer centers:
http://www.intel.com/cd/ids/developer/asmo-na/eng/dc/index.htm
•
Processor support general link:
http://www.intel.com/support/processors/
•
Software products and packages:
http://www.intel.com/cd/software/products/asmo-na/eng/index.htm
•
Intel 64 and IA-32 processor manuals (printed or PDF downloads):
http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html.html
•
Intel® Multi-Core Technology:
•
Intel® Hyper-Threading Technology (Intel® HT Technology):
http://software.intel.com/partner/multicore
http://www.intel.com/technology/platform-technology/hyper-threading/index.htm
Vol. 3A 1-9
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CHAPTER 2
SYSTEM ARCHITECTURE OVERVIEW
IA-32 architecture (beginning with the Intel386 processor family) provides extensive support for operating-system
and system-development software. This support offers multiple modes of operation, which include:
•
Real mode, protected mode, virtual 8086 mode, and system management mode. These are sometimes
referred to as legacy modes.
Intel 64 architecture supports almost all the system programming facilities available in IA-32 architecture and
extends them to a new operating mode (IA-32e mode) that supports a 64-bit programming environment. IA-32e
mode allows software to operate in one of two sub-modes:
•
•
64-bit mode supports 64-bit OS and 64-bit applications
Compatibility mode allows most legacy software to run; it co-exists with 64-bit applications under a 64-bit OS.
The IA-32 system-level architecture and includes features to assist in the following operations:
•
•
•
•
•
•
•
•
Memory management
Protection of software modules
Multitasking
Exception and interrupt handling
Multiprocessing
Cache management
Hardware resource and power management
Debugging and performance monitoring
This chapter provides a description of each part of this architecture. It also describes the system registers that are
used to set up and control the processor at the system level and gives a brief overview of the processor’s systemlevel (operating system) instructions.
Many features of the system-level architectural are used only by system programmers. However, application
programmers may need to read this chapter and the following chapters in order to create a reliable and secure
environment for application programs.
This overview and most subsequent chapters of this book focus on protected-mode operation of the IA-32 architecture. IA-32e mode operation of the Intel 64 architecture, as it differs from protected mode operation, is also
described.
All Intel 64 and IA-32 processors enter real-address mode following a power-up or reset (see Chapter 9, “Processor
Management and Initialization”). Software then initiates the switch from real-address mode to protected mode. If
IA-32e mode operation is desired, software also initiates a switch from protected mode to IA-32e mode.
2.1
OVERVIEW OF THE SYSTEM-LEVEL ARCHITECTURE
System-level architecture consists of a set of registers, data structures, and instructions designed to support basic
system-level operations such as memory management, interrupt and exception handling, task management, and
control of multiple processors.
Figure 2-1 provides a summary of system registers and data structures that applies to 32-bit modes. System registers and data structures that apply to IA-32e mode are shown in Figure 2-2.
Vol. 3A 2-1
SYSTEM ARCHITECTURE OVERVIEW
Physical Address
EFLAGS Register
Control Registers
CR4
CR3
CR2
CR1
CR0
Task Register
Interrupt
Vector
Code, Data or
Stack Segment
Linear Address
Task-State
Segment (TSS)
Segment Selector
Register
Global Descriptor
Table (GDT)
Segment Sel.
Seg. Desc.
TSS Seg. Sel.
TSS Desc.
Interrupt Handler
Code
Current
Stack
TSS
Seg. Desc.
Interrupt Descriptor
Table (IDT)
Task-State
Segment (TSS)
TSS Desc.
Interrupt Gate
Task
Code
Data
Stack
LDT Desc.
Task Gate
Task
Code
Data
Stack
GDTR
Trap Gate
Local Descriptor
Table (LDT)
IDTR
Call-Gate
Segment Selector
Seg. Desc.
Call Gate
XCR0 (XFEM)
Protected Procedure
Code
Current
Stack
TSS
LDTR
Linear Address Space
Dir
Linear Addr.
Exception Handler
Code
Current
Stack
TSS
Linear Address
Table
Offset
Page Directory
Page Table
Pg. Dir. Entry
Pg. Tbl. Entry
Page
Physical Addr.
0
CR3*
This page mapping example is for 4-KByte pages
and the normal 32-bit physical address size.
*Physical Address
Figure 2-1. IA-32 System-Level Registers and Data Structures
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SYSTEM ARCHITECTURE OVERVIEW
RFLAGS
Physical Address
Control Register
CR8
CR4
CR3
CR2
CR1
CR0
Task Register
Interrupt
Vector
Code, Data or Stack
Segment (Base =0)
Linear Address
Task-State
Segment (TSS)
Segment Selector
Register
Global Descriptor
Table (GDT)
Segment Sel.
Seg. Desc.
TR
TSS Desc.
NULL
Seg. Desc.
Interrupt Descriptor
Table (IDT)
Interr. Handler
Seg. Desc.
Interrupt Gate
LDT Desc.
GDTR
IST
Trap Gate
Local Descriptor
Table (LDT)
NULL
Call-Gate
Segment Selector
Seg. Desc.
Call Gate
XCR0 (XFEM)
NULL
LDTR
Linear Address Space
Linear Addr.
Code
Current TSS
Stack
Interrupt Gate
IDTR
Interrupt Handler
Code
Stack
Linear Address
PML4 Dir. Pointer Directory
PML4
Pg. Dir. Ptr.
Pg. Dir.
Entry
PML4.
Entry
0
CR3*
Page Dir.
Table
Exception Handler
Code
Stack
Protected Procedure
Code
Stack
Offset
Page Table
Page Tbl
Entry
Page
Physical
Addr.
This page mapping example is for 4-KByte pages
and 40-bit physical address size.
*Physical Address
Figure 2-2. System-Level Registers and Data Structures in IA-32e Mode
2.1.1
Global and Local Descriptor Tables
When operating in protected mode, all memory accesses pass through either the global descriptor table (GDT) or
an optional local descriptor table (LDT) as shown in Figure 2-1. These tables contain entries called segment
descriptors. Segment descriptors provide the base address of segments well as access rights, type, and usage
information.
Each segment descriptor has an associated segment selector. A segment selector provides the software that uses
it with an index into the GDT or LDT (the offset of its associated segment descriptor), a global/local flag (determines whether the selector points to the GDT or the LDT), and access rights information.
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SYSTEM ARCHITECTURE OVERVIEW
To access a byte in a segment, a segment selector and an offset must be supplied. The segment selector provides
access to the segment descriptor for the segment (in the GDT or LDT). From the segment descriptor, the processor
obtains the base address of the segment in the linear address space. The offset then provides the location of the
byte relative to the base address. This mechanism can be used to access any valid code, data, or stack segment,
provided the segment is accessible from the current privilege level (CPL) at which the processor is operating. The
CPL is defined as the protection level of the currently executing code segment.
See Figure 2-1. The solid arrows in the figure indicate a linear address, dashed lines indicate a segment selector,
and the dotted arrows indicate a physical address. For simplicity, many of the segment selectors are shown as
direct pointers to a segment. However, the actual path from a segment selector to its associated segment is always
through a GDT or LDT.
The linear address of the base of the GDT is contained in the GDT register (GDTR); the linear address of the LDT is
contained in the LDT register (LDTR).
2.1.1.1
Global and Local Descriptor Tables in IA-32e Mode
GDTR and LDTR registers are expanded to 64-bits wide in both IA-32e sub-modes (64-bit mode and compatibility
mode). For more information: see Section 3.5.2, “Segment Descriptor Tables in IA-32e Mode.”
Global and local descriptor tables are expanded in 64-bit mode to support 64-bit base addresses, (16-byte LDT
descriptors hold a 64-bit base address and various attributes). In compatibility mode, descriptors are not
expanded.
2.1.2
System Segments, Segment Descriptors, and Gates
Besides code, data, and stack segments that make up the execution environment of a program or procedure, the
architecture defines two system segments: the task-state segment (TSS) and the LDT. The GDT is not considered
a segment because it is not accessed by means of a segment selector and segment descriptor. TSSs and LDTs have
segment descriptors defined for them.
The architecture also defines a set of special descriptors called gates (call gates, interrupt gates, trap gates, and
task gates). These provide protected gateways to system procedures and handlers that may operate at a different
privilege level than application programs and most procedures. For example, a CALL to a call gate can provide
access to a procedure in a code segment that is at the same or a numerically lower privilege level (more privileged)
than the current code segment. To access a procedure through a call gate, the calling procedure1 supplies the
selector for the call gate. The processor then performs an access rights check on the call gate, comparing the CPL
with the privilege level of the call gate and the destination code segment pointed to by the call gate.
If access to the destination code segment is allowed, the processor gets the segment selector for the destination
code segment and an offset into that code segment from the call gate. If the call requires a change in privilege
level, the processor also switches to the stack for the targeted privilege level. The segment selector for the new
stack is obtained from the TSS for the currently running task. Gates also facilitate transitions between 16-bit and
32-bit code segments, and vice versa.
2.1.2.1
Gates in IA-32e Mode
In IA-32e mode, the following descriptors are 16-byte descriptors (expanded to allow a 64-bit base): LDT descriptors, 64-bit TSSs, call gates, interrupt gates, and trap gates.
Call gates facilitate transitions between 64-bit mode and compatibility mode. Task gates are not supported in IA32e mode. On privilege level changes, stack segment selectors are not read from the TSS. Instead, they are set to
NULL.
1. The word “procedure” is commonly used in this document as a general term for a logical unit or block of code (such as a program, procedure, function, or routine).
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SYSTEM ARCHITECTURE OVERVIEW
2.1.3
Task-State Segments and Task Gates
The TSS (see Figure 2-1) defines the state of the execution environment for a task. It includes the state of generalpurpose registers, segment registers, the EFLAGS register, the EIP register, and segment selectors with stack
pointers for three stack segments (one stack for each privilege level). The TSS also includes the segment selector
for the LDT associated with the task and the base address of the paging-structure hierarchy.
All program execution in protected mode happens within the context of a task (called the current task). The
segment selector for the TSS for the current task is stored in the task register. The simplest method for switching
to a task is to make a call or jump to the new task. Here, the segment selector for the TSS of the new task is given
in the CALL or JMP instruction. In switching tasks, the processor performs the following actions:
1. Stores the state of the current task in the current TSS.
2. Loads the task register with the segment selector for the new task.
3. Accesses the new TSS through a segment descriptor in the GDT.
4. Loads the state of the new task from the new TSS into the general-purpose registers, the segment registers,
the LDTR, control register CR3 (base address of the paging-structure hierarchy), the EFLAGS register, and the
EIP register.
5. Begins execution of the new task.
A task can also be accessed through a task gate. A task gate is similar to a call gate, except that it provides access
(through a segment selector) to a TSS rather than a code segment.
2.1.3.1
Task-State Segments in IA-32e Mode
Hardware task switches are not supported in IA-32e mode. However, TSSs continue to exist. The base address of
a TSS is specified by its descriptor.
A 64-bit TSS holds the following information that is important to 64-bit operation:
•
•
•
Stack pointer addresses for each privilege level
Pointer addresses for the interrupt stack table
Offset address of the IO-permission bitmap (from the TSS base)
The task register is expanded to hold 64-bit base addresses in IA-32e mode. See also: Section 7.7, “Task Management in 64-bit Mode.”
2.1.4
Interrupt and Exception Handling
External interrupts, software interrupts and exceptions are handled through the interrupt descriptor table (IDT).
The IDT stores a collection of gate descriptors that provide access to interrupt and exception handlers. Like the
GDT, the IDT is not a segment. The linear address for the base of the IDT is contained in the IDT register (IDTR).
Gate descriptors in the IDT can be interrupt, trap, or task gate descriptors. To access an interrupt or exception
handler, the processor first receives an interrupt vector (interrupt number) from internal hardware, an external
interrupt controller, or from software by means of an INT, INTO, INT 3, or BOUND instruction. The interrupt vector
provides an index into the IDT. If the selected gate descriptor is an interrupt gate or a trap gate, the associated
handler procedure is accessed in a manner similar to calling a procedure through a call gate. If the descriptor is a
task gate, the handler is accessed through a task switch.
2.1.4.1
Interrupt and Exception Handling IA-32e Mode
In IA-32e mode, interrupt descriptors are expanded to 16 bytes to support 64-bit base addresses. This is true for
64-bit mode and compatibility mode.
The IDTR register is expanded to hold a 64-bit base address. Task gates are not supported.
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SYSTEM ARCHITECTURE OVERVIEW
2.1.5
Memory Management
System architecture supports either direct physical addressing of memory or virtual memory (through paging).
When physical addressing is used, a linear address is treated as a physical address. When paging is used: all code,
data, stack, and system segments (including the GDT and IDT) can be paged with only the most recently accessed
pages being held in physical memory.
The location of pages (sometimes called page frames) in physical memory is contained in the paging structures.
These structures reside in physical memory (see Figure 2-1 for the case of 32-bit paging).
The base physical address of the paging-structure hierarchy is contained in control register CR3. The entries in the
paging structures determine the physical address of the base of a page frame, access rights and memory management information.
To use this paging mechanism, a linear address is broken into parts. The parts provide separate offsets into the
paging structures and the page frame. A system can have a single hierarchy of paging structures or several. For
example, each task can have its own hierarchy.
2.1.5.1
Memory Management in IA-32e Mode
In IA-32e mode, physical memory pages are managed by a set of system data structures. In compatibility mode
and 64-bit mode, four levels of system data structures are used. These include:
•
The page map level 4 (PML4) — An entry in a PML4 table contains the physical address of the base of a page
directory pointer table, access rights, and memory management information. The base physical address of the
PML4 is stored in CR3.
•
A set of page directory pointer tables — An entry in a page directory pointer table contains the physical
address of the base of a page directory table, access rights, and memory management information.
•
Sets of page directories — An entry in a page directory table contains the physical address of the base of a
page table, access rights, and memory management information.
•
Sets of page tables — An entry in a page table contains the physical address of a page frame, access rights,
and memory management information.
2.1.6
System Registers
To assist in initializing the processor and controlling system operations, the system architecture provides system
flags in the EFLAGS register and several system registers:
•
The system flags and IOPL field in the EFLAGS register control task and mode switching, interrupt handling,
instruction tracing, and access rights. See also: Section 2.3, “System Flags and Fields in the EFLAGS Register.”
•
The control registers (CR0, CR2, CR3, and CR4) contain a variety of flags and data fields for controlling systemlevel operations. Other flags in these registers are used to indicate support for specific processor capabilities
within the operating system or executive. See also: Section 2.5, “Control Registers.”
•
The debug registers (not shown in Figure 2-1) allow the setting of breakpoints for use in debugging programs
and systems software. See also: Chapter 17, “Debugging, Branch Profiling, and Time-Stamp Counter.”
•
The GDTR, LDTR, and IDTR registers contain the linear addresses and sizes (limits) of their respective tables.
See also: Section 2.4, “Memory-Management Registers.”
•
The task register contains the linear address and size of the TSS for the current task. See also: Section 2.4,
“Memory-Management Registers.”
•
Model-specific registers (not shown in Figure 2-1).
The model-specific registers (MSRs) are a group of registers available primarily to operating-system or executive
procedures (that is, code running at privilege level 0). These registers control items such as the debug extensions,
the performance-monitoring counters, the machine- check architecture, and the memory type ranges (MTRRs).
The number and function of these registers varies among different members of the Intel 64 and IA-32 processor
families. See also: Section 9.4, “Model-Specific Registers (MSRs),” and Chapter 35, “Model-Specific Registers
(MSRs).”
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SYSTEM ARCHITECTURE OVERVIEW
Most systems restrict access to system registers (other than the EFLAGS register) by application programs.
Systems can be designed, however, where all programs and procedures run at the most privileged level (privilege
level 0). In such a case, application programs would be allowed to modify the system registers.
2.1.6.1
System Registers in IA-32e Mode
In IA-32e mode, the four system-descriptor-table registers (GDTR, IDTR, LDTR, and TR) are expanded in hardware
to hold 64-bit base addresses. EFLAGS becomes the 64-bit RFLAGS register. CR0–CR4 are expanded to 64 bits.
CR8 becomes available. CR8 provides read-write access to the task priority register (TPR) so that the operating
system can control the priority classes of external interrupts.
In 64-bit mode, debug registers DR0–DR7 are 64 bits. In compatibility mode, address-matching in DR0–DR3 is
also done at 64-bit granularity.
On systems that support IA-32e mode, the extended feature enable register (IA32_EFER) is available. This modelspecific register controls activation of IA-32e mode and other IA-32e mode operations. In addition, there are
several model-specific registers that govern IA-32e mode instructions:
•
•
•
•
IA32_KernelGSbase — Used by SWAPGS instruction.
IA32_LSTAR — Used by SYSCALL instruction.
IA32_SYSCALL_FLAG_MASK — Used by SYSCALL instruction.
IA32_STAR_CS — Used by SYSCALL and SYSRET instruction.
2.1.7
Other System Resources
Besides the system registers and data structures described in the previous sections, system architecture provides
the following additional resources:
•
•
•
Operating system instructions (see also: Section 2.7, “System Instruction Summary”).
Performance-monitoring counters (not shown in Figure 2-1).
Internal caches and buffers (not shown in Figure 2-1).
Performance-monitoring counters are event counters that can be programmed to count processor events such as
the number of instructions decoded, the number of interrupts received, or the number of cache loads. See also:
Chapter 23, “Introduction to Virtual-Machine Extensions.”
The processor provides several internal caches and buffers. The caches are used to store both data and instructions. The buffers are used to store things like decoded addresses to system and application segments and write
operations waiting to be performed. See also: Chapter 11, “Memory Cache Control.”
2.2
MODES OF OPERATION
The IA-32 supports three operating modes and one quasi-operating mode:
•
Protected mode — This is the native operating mode of the processor. It provides a rich set of architectural
features, flexibility, high performance and backward compatibility to existing software base.
•
Real-address mode — This operating mode provides the programming environment of the Intel 8086
processor, with a few extensions (such as the ability to switch to protected or system management mode).
•
System management mode (SMM) — SMM is a standard architectural feature in all IA-32 processors,
beginning with the Intel386 SL processor. This mode provides an operating system or executive with a
transparent mechanism for implementing power management and OEM differentiation features. SMM is
entered through activation of an external system interrupt pin (SMI#), which generates a system management
interrupt (SMI). In SMM, the processor switches to a separate address space while saving the context of the
currently running program or task. SMM-specific code may then be executed transparently. Upon returning
from SMM, the processor is placed back into its state prior to the SMI.
•
Virtual-8086 mode — In protected mode, the processor supports a quasi-operating mode known as virtual8086 mode. This mode allows the processor execute 8086 software in a protected, multitasking environment.
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SYSTEM ARCHITECTURE OVERVIEW
Intel 64 architecture supports all operating modes of IA-32 architecture and IA-32e modes:
•
IA-32e mode — In IA-32e mode, the processor supports two sub-modes: compatibility mode and 64-bit
mode. 64-bit mode provides 64-bit linear addressing and support for physical address space larger than 64
GBytes. Compatibility mode allows most legacy protected-mode applications to run unchanged.
Figure 2-3 shows how the processor moves between operating modes.
SMI#
Real-Address
Mode
Reset or
PE=0
PE=1
Reset
or
RSM
SMI#
Reset
Protected Mode
See**
VM=0
RSM
LME=1, CR0.PG=1*
SMI#
IA-32e
Mode
RSM
System
Management
Mode
VM=1
* See Section 9.8.5
Virtual-8086
Mode
SMI#
** See Section 9.8.5.4
RSM
Figure 2-3. Transitions Among the Processor’s Operating Modes
The processor is placed in real-address mode following power-up or a reset. The PE flag in control register CR0 then
controls whether the processor is operating in real-address or protected mode. See also: Section 9.9, “Mode
Switching.” and Section 4.1.2, “Paging-Mode Enabling.”
The VM flag in the EFLAGS register determines whether the processor is operating in protected mode or virtual8086 mode. Transitions between protected mode and virtual-8086 mode are generally carried out as part of a task
switch or a return from an interrupt or exception handler. See also: Section 20.2.5, “Entering Virtual-8086 Mode.”
The LMA bit (IA32_EFER.LMA[bit 10]) determines whether the processor is operating in IA-32e mode. When
running in IA-32e mode, 64-bit or compatibility sub-mode operation is determined by CS.L bit of the code segment.
The processor enters into IA-32e mode from protected mode by enabling paging and setting the LME bit
(IA32_EFER.LME[bit 8]). See also: Chapter 9, “Processor Management and Initialization.”
The processor switches to SMM whenever it receives an SMI while the processor is in real-address, protected,
virtual-8086, or IA-32e modes. Upon execution of the RSM instruction, the processor always returns to the mode
it was in when the SMI occurred.
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SYSTEM ARCHITECTURE OVERVIEW
2.2.1
Extended Feature Enable Register
The IA32_EFER MSR provides several fields related to IA-32e mode enabling and operation. It also provides one
field that relates to page-access right modification (see Section 4.6, “Access Rights”). The layout of the
IA32_EFER MSR is shown in Figure 2-4.
63
12 11 10 9 8 7
1
0
IA32_EFER
Execute Disable Bit Enable
IA-32e Mode Active
IA-32e Mode Enable
SYSCALL Enable
Reserved
Figure 2-4. IA32_EFER MSR Layout
Table 2-1. IA32_EFER MSR Information
Bit
Description
0
SYSCALL Enable (R/W)
Enables SYSCALL/SYSRET instructions in 64-bit mode.
7:1
Reserved.
8
IA-32e Mode Enable (R/W)
Enables IA-32e mode operation.
9
Reserved.
10
IA-32e Mode Active (R)
Indicates IA-32e mode is active when set.
11
Execute Disable Bit Enable (R/W)
Enables page access restriction by preventing instruction fetches from PAE pages with the XD bit set (See Section 4.6).
63:12
2.3
Reserved.
SYSTEM FLAGS AND FIELDS IN THE EFLAGS REGISTER
The system flags and IOPL field of the EFLAGS register control I/O, maskable hardware interrupts, debugging, task
switching, and the virtual-8086 mode (see Figure 2-5). Only privileged code (typically operating system or executive code) should be allowed to modify these bits.
The system flags and IOPL are:
TF
Trap (bit 8) — Set to enable single-step mode for debugging; clear to disable single-step mode. In singlestep mode, the processor generates a debug exception after each instruction. This allows the execution
state of a program to be inspected after each instruction. If an application program sets the TF flag using
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SYSTEM ARCHITECTURE OVERVIEW
a POPF, POPFD, or IRET instruction, a debug exception is generated after the instruction that follows the
POPF, POPFD, or IRET.
31
22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Reserved (set to 0)
V V
I I I A V R 0 N
T
D
C M F
P F
I
O
P
L
O D I T S Z
P
C
A
F F F F F F 0 F 0 F 1 F
ID — Identification Flag
VIP — Virtual Interrupt Pending
VIF — Virtual Interrupt Flag
AC — Alignment Check
VM — Virtual-8086 Mode
RF — Resume Flag
NT — Nested Task Flag
IOPL— I/O Privilege Level
IF — Interrupt Enable Flag
TF — Trap Flag
Reserved
Figure 2-5. System Flags in the EFLAGS Register
IF
Interrupt enable (bit 9) — Controls the response of the processor to maskable hardware interrupt
requests (see also: Section 6.3.2, “Maskable Hardware Interrupts”). The flag is set to respond to maskable
hardware interrupts; cleared to inhibit maskable hardware interrupts. The IF flag does not affect the generation of exceptions or nonmaskable interrupts (NMI interrupts). The CPL, IOPL, and the state of the VME
flag in control register CR4 determine whether the IF flag can be modified by the CLI, STI, POPF, POPFD,
and IRET.
IOPL
I/O privilege level field (bits 12 and 13) — Indicates the I/O privilege level (IOPL) of the currently
running program or task. The CPL of the currently running program or task must be less than or equal to
the IOPL to access the I/O address space. This field can only be modified by the POPF and IRET instructions
when operating at a CPL of 0.
The IOPL is also one of the mechanisms that controls the modification of the IF flag and the handling of
interrupts in virtual-8086 mode when virtual mode extensions are in effect (when CR4.VME = 1). See also:
Chapter 14, “Input/Output,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 1.
NT
Nested task (bit 14) — Controls the chaining of interrupted and called tasks. The processor sets this flag
on calls to a task initiated with a CALL instruction, an interrupt, or an exception. It examines and modifies
this flag on returns from a task initiated with the IRET instruction. The flag can be explicitly set or cleared
with the POPF/POPFD instructions; however, changing to the state of this flag can generate unexpected
exceptions in application programs.
See also: Section 7.4, “Task Linking.”
RF
Resume (bit 16) — Controls the processor’s response to instruction-breakpoint conditions. When set, this
flag temporarily disables debug exceptions (#DB) from being generated for instruction breakpoints
(although other exception conditions can cause an exception to be generated). When clear, instruction
breakpoints will generate debug exceptions.
The primary function of the RF flag is to allow the restarting of an instruction following a debug exception
that was caused by an instruction breakpoint condition. Here, debug software must set this flag in the
EFLAGS image on the stack just prior to returning to the interrupted program with IRETD (to prevent the
instruction breakpoint from causing another debug exception). The processor then automatically clears
this flag after the instruction returned to has been successfully executed, enabling instruction breakpoint
faults again.
See also: Section 17.3.1.1, “Instruction-Breakpoint Exception Condition.”
VM
Virtual-8086 mode (bit 17) — Set to enable virtual-8086 mode; clear to return to protected mode.
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SYSTEM ARCHITECTURE OVERVIEW
See also: Section 20.2.1, “Enabling Virtual-8086 Mode.”
AC
Alignment check (bit 18) — Set this flag and the AM flag in control register CR0 to enable alignment
checking of memory references; clear the AC flag and/or the AM flag to disable alignment checking. An
alignment-check exception is generated when reference is made to an unaligned operand, such as a word
at an odd byte address or a doubleword at an address which is not an integral multiple of four. Alignmentcheck exceptions are generated only in user mode (privilege level 3). Memory references that default to
privilege level 0, such as segment descriptor loads, do not generate this exception even when caused by
instructions executed in user-mode.
The alignment-check exception can be used to check alignment of data. This is useful when exchanging
data with processors which require all data to be aligned. The alignment-check exception can also be used
by interpreters to flag some pointers as special by misaligning the pointer. This eliminates overhead of
checking each pointer and only handles the special pointer when used.
VIF
Virtual Interrupt (bit 19) — Contains a virtual image of the IF flag. This flag is used in conjunction with
the VIP flag. The processor only recognizes the VIF flag when either the VME flag or the PVI flag in control
register CR4 is set and the IOPL is less than 3. (The VME flag enables the virtual-8086 mode extensions;
the PVI flag enables the protected-mode virtual interrupts.)
See also: Section 20.3.3.5, “Method 6: Software Interrupt Handling,” and Section 20.4, “Protected-Mode
Virtual Interrupts.”
VIP
Virtual interrupt pending (bit 20) — Set by software to indicate that an interrupt is pending; cleared to
indicate that no interrupt is pending. This flag is used in conjunction with the VIF flag. The processor reads
this flag but never modifies it. The processor only recognizes the VIP flag when either the VME flag or the
PVI flag in control register CR4 is set and the IOPL is less than 3. The VME flag enables the virtual-8086
mode extensions; the PVI flag enables the protected-mode virtual interrupts.
See Section 20.3.3.5, “Method 6: Software Interrupt Handling,” and Section 20.4, “Protected-Mode Virtual
Interrupts.”
ID
2.3.1
Identification (bit 21). — The ability of a program or procedure to set or clear this flag indicates support
for the CPUID instruction.
System Flags and Fields in IA-32e Mode
In 64-bit mode, the RFLAGS register expands to 64 bits with the upper 32 bits reserved. System flags in RFLAGS
(64-bit mode) or EFLAGS (compatibility mode) are shown in Figure 2-5.
In IA-32e mode, the processor does not allow the VM bit to be set because virtual-8086 mode is not supported
(attempts to set the bit are ignored). Also, the processor will not set the NT bit. The processor does, however, allow
software to set the NT bit (note that an IRET causes a general protection fault in IA-32e mode if the NT bit is set).
In IA-32e mode, the SYSCALL/SYSRET instructions have a programmable method of specifying which bits are
cleared in RFLAGS/EFLAGS. These instructions save/restore EFLAGS/RFLAGS.
2.4
MEMORY-MANAGEMENT REGISTERS
The processor provides four memory-management registers (GDTR, LDTR, IDTR, and TR) that specify the locations
of the data structures which control segmented memory management (see Figure 2-6). Special instructions are
provided for loading and storing these registers.
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SYSTEM ARCHITECTURE OVERVIEW
47(79)
System Table Registers
16 15
0
GDTR
32(64)-bit Linear Base Address
16-Bit Table Limit
IDTR
32(64)-bit Linear Base Address
16-Bit Table Limit
System Segment
Registers
15
0
Task
Register
LDTR
Segment Descriptor Registers (Automatically Loaded)
Attributes
Seg. Sel.
32(64)-bit Linear Base Address
Segment Limit
Seg. Sel.
32(64)-bit Linear Base Address
Segment Limit
Figure 2-6. Memory Management Registers
2.4.1
Global Descriptor Table Register (GDTR)
The GDTR register holds the base address (32 bits in protected mode; 64 bits in IA-32e mode) and the 16-bit table
limit for the GDT. The base address specifies the linear address of byte 0 of the GDT; the table limit specifies the
number of bytes in the table.
The LGDT and SGDT instructions load and store the GDTR register, respectively. On power up or reset of the
processor, the base address is set to the default value of 0 and the limit is set to 0FFFFH. A new base address must
be loaded into the GDTR as part of the processor initialization process for protected-mode operation.
See also: Section 3.5.1, “Segment Descriptor Tables.”
2.4.2
Local Descriptor Table Register (LDTR)
The LDTR register holds the 16-bit segment selector, base address (32 bits in protected mode; 64 bits in IA-32e
mode), segment limit, and descriptor attributes for the LDT. The base address specifies the linear address of byte
0 of the LDT segment; the segment limit specifies the number of bytes in the segment. See also: Section 3.5.1,
“Segment Descriptor Tables.”
The LLDT and SLDT instructions load and store the segment selector part of the LDTR register, respectively. The
segment that contains the LDT must have a segment descriptor in the GDT. When the LLDT instruction loads a
segment selector in the LDTR: the base address, limit, and descriptor attributes from the LDT descriptor are automatically loaded in the LDTR.
When a task switch occurs, the LDTR is automatically loaded with the segment selector and descriptor for the LDT
for the new task. The contents of the LDTR are not automatically saved prior to writing the new LDT information
into the register.
On power up or reset of the processor, the segment selector and base address are set to the default value of 0 and
the limit is set to 0FFFFH.
2.4.3
IDTR Interrupt Descriptor Table Register
The IDTR register holds the base address (32 bits in protected mode; 64 bits in IA-32e mode) and 16-bit table limit
for the IDT. The base address specifies the linear address of byte 0 of the IDT; the table limit specifies the number
of bytes in the table. The LIDT and SIDT instructions load and store the IDTR register, respectively. On power up or
reset of the processor, the base address is set to the default value of 0 and the limit is set to 0FFFFH. The base
address and limit in the register can then be changed as part of the processor initialization process.
See also: Section 6.10, “Interrupt Descriptor Table (IDT).”
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SYSTEM ARCHITECTURE OVERVIEW
2.4.4
Task Register (TR)
The task register holds the 16-bit segment selector, base address (32 bits in protected mode; 64 bits in IA-32e
mode), segment limit, and descriptor attributes for the TSS of the current task. The selector references the TSS
descriptor in the GDT. The base address specifies the linear address of byte 0 of the TSS; the segment limit specifies the number of bytes in the TSS. See also: Section 7.2.4, “Task Register.”
The LTR and STR instructions load and store the segment selector part of the task register, respectively. When the
LTR instruction loads a segment selector in the task register, the base address, limit, and descriptor attributes from
the TSS descriptor are automatically loaded into the task register. On power up or reset of the processor, the base
address is set to the default value of 0 and the limit is set to 0FFFFH.
When a task switch occurs, the task register is automatically loaded with the segment selector and descriptor for
the TSS for the new task. The contents of the task register are not automatically saved prior to writing the new TSS
information into the register.
2.5
CONTROL REGISTERS
Control registers (CR0, CR1, CR2, CR3, and CR4; see Figure 2-7) determine operating mode of the processor and
the characteristics of the currently executing task. These registers are 32 bits in all 32-bit modes and compatibility
mode.
In 64-bit mode, control registers are expanded to 64 bits. The MOV CRn instructions are used to manipulate the
register bits. Operand-size prefixes for these instructions are ignored. The following is also true:
•
Bits 63:32 of CR0 and CR4 are reserved and must be written with zeros. Writing a nonzero value to any of the
upper 32 bits results in a general-protection exception, #GP(0).
•
•
•
All 64 bits of CR2 are writable by software.
•
Register CR8 is available in 64-bit mode only.
Bits 51:40 of CR3 are reserved and must be 0.
The MOV CRn instructions do not check that addresses written to CR2 and CR3 are within the linear-address or
physical-address limitations of the implementation.
The control registers are summarized below, and each architecturally defined control field in these control registers
are described individually. In Figure 2-7, the width of the register in 64-bit mode is indicated in parenthesis (except
for CR0).
•
•
•
•
CR0 — Contains system control flags that control operating mode and states of the processor.
CR1 — Reserved.
CR2 — Contains the page-fault linear address (the linear address that caused a page fault).
CR3 — Contains the physical address of the base of the paging-structure hierarchy and two flags (PCD and
PWT). Only the most-significant bits (less the lower 12 bits) of the base address are specified; the lower 12 bits
of the address are assumed to be 0. The first paging structure must thus be aligned to a page (4-KByte)
boundary. The PCD and PWT flags control caching of that paging structure in the processor’s internal data
caches (they do not control TLB caching of page-directory information).
When using the physical address extension, the CR3 register contains the base address of the page-directorypointer table In IA-32e mode, the CR3 register contains the base address of the PML4 table.
See also: Chapter 4, “Paging.”
•
CR4 — Contains a group of flags that enable several architectural extensions, and indicate operating system or
executive support for specific processor capabilities. The control registers can be read and loaded (or modified)
using the move-to-or-from-control-registers forms of the MOV instruction. In protected mode, the MOV
instructions allow the control registers to be read or loaded (at privilege level 0 only). This restriction means
that application programs or operating-system procedures (running at privilege levels 1, 2, or 3) are prevented
from reading or loading the control registers.
Vol. 3A 2-13
SYSTEM ARCHITECTURE OVERVIEW
•
CR8 — Provides read and write access to the Task Priority Register (TPR). It specifies the priority threshold
value that operating systems use to control the priority class of external interrupts allowed to interrupt the
processor. This register is available only in 64-bit mode. However, interrupt filtering continues to apply in
compatibility mode.
31(63)
20
Reserved
18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
S
M
E
P
S
M
X
E
OSXSAVE
V
M
X
E
T P V
P P M P P
C G C A S D S V M
E D I E
E E E E E
FSGSBASE
PCIDE
OSFXSR
OSXMMEXCPT
12 11
5 4 3 2
31(63)
P P
C W
D T
Page-Directory Base
31(63)
CR4
CR3
(PDBR)
0
Page-Fault Linear Address
31(63)
CR2
0
CR1
31 30 29 28
P C N
G D W
19 18 17 16 15
A
M
W
P
6 5 4 3 2 1 0
N E T E M P
E T S M P E
CR0
Reserved
Figure 2-7. Control Registers
When loading a control register, reserved bits should always be set to the values previously read. The flags in
control registers are:
PG
Paging (bit 31 of CR0) — Enables paging when set; disables paging when clear. When paging is
disabled, all linear addresses are treated as physical addresses. The PG flag has no effect if the PE flag (bit
0 of register CR0) is not also set; setting the PG flag when the PE flag is clear causes a general-protection
exception (#GP). See also: Chapter 4, “Paging.”
On Intel 64 processors, enabling and disabling IA-32e mode operation also requires modifying CR0.PG.
CD
Cache Disable (bit 30 of CR0) — When the CD and NW flags are clear, caching of memory locations for
the whole of physical memory in the processor’s internal (and external) caches is enabled. When the CD
flag is set, caching is restricted as described in Table 11-5. To prevent the processor from accessing and
updating its caches, the CD flag must be set and the caches must be invalidated so that no cache hits can
occur.
See also: Section 11.5.3, “Preventing Caching,” and Section 11.5, “Cache Control.”
NW
Not Write-through (bit 29 of CR0) — When the NW and CD flags are clear, write-back (for Pentium 4,
Intel Xeon, P6 family, and Pentium processors) or write-through (for Intel486 processors) is enabled for
writes that hit the cache and invalidation cycles are enabled. See Table 11-5 for detailed information about
the affect of the NW flag on caching for other settings of the CD and NW flags.
AM
Alignment Mask (bit 18 of CR0) — Enables automatic alignment checking when set; disables alignment
checking when clear. Alignment checking is performed only when the AM flag is set, the AC flag in the
EFLAGS register is set, CPL is 3, and the processor is operating in either protected or virtual-8086 mode.
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SYSTEM ARCHITECTURE OVERVIEW
WP
Write Protect (bit 16 of CR0) — When set, inhibits supervisor-level procedures from writing into readonly pages; when clear, allows supervisor-level procedures to write into read-only pages (regardless of the
U/S bit setting; see Section 4.1.3 and Section 4.6). This flag facilitates implementation of the copy-onwrite method of creating a new process (forking) used by operating systems such as UNIX.
NE
Numeric Error (bit 5 of CR0) — Enables the native (internal) mechanism for reporting x87 FPU errors
when set; enables the PC-style x87 FPU error reporting mechanism when clear. When the NE flag is clear
and the IGNNE# input is asserted, x87 FPU errors are ignored. When the NE flag is clear and the IGNNE#
input is deasserted, an unmasked x87 FPU error causes the processor to assert the FERR# pin to generate
an external interrupt and to stop instruction execution immediately before executing the next waiting
floating-point instruction or WAIT/FWAIT instruction.
The FERR# pin is intended to drive an input to an external interrupt controller (the FERR# pin emulates the
ERROR# pin of the Intel 287 and Intel 387 DX math coprocessors). The NE flag, IGNNE# pin, and FERR#
pin are used with external logic to implement PC-style error reporting. Using FERR# and IGNNE# to handle
floating-point exceptions is deprecated by modern operating systems; this non-native approach also limits
newer processors to operate with one logical processor active.
See also: “Software Exception Handling” in Chapter 8, “Programming with the x87 FPU,” and Appendix A,
“EFLAGS Cross-Reference,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 1.
ET
Extension Type (bit 4 of CR0) — Reserved in the Pentium 4, Intel Xeon, P6 family, and Pentium processors. In the Pentium 4, Intel Xeon, and P6 family processors, this flag is hardcoded to 1. In the Intel386
and Intel486 processors, this flag indicates support of Intel 387 DX math coprocessor instructions when
set.
TS
Task Switched (bit 3 of CR0) — Allows the saving of the x87 FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4
context on a task switch to be delayed until an x87 FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instruction is
actually executed by the new task. The processor sets this flag on every task switch and tests it when
executing x87 FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instructions.
•
If the TS flag is set and the EM flag (bit 2 of CR0) is clear, a device-not-available exception (#NM) is
raised prior to the execution of any x87 FPU/MMX/SSE/ SSE2/SSE3/SSSE3/SSE4 instruction; with the
exception of PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE, MOVNTI, CLFLUSH, CRC32, and POPCNT.
See the paragraph below for the special case of the WAIT/FWAIT instructions.
•
If the TS flag is set and the MP flag (bit 1 of CR0) and EM flag are clear, an #NM exception is not raised
prior to the execution of an x87 FPU WAIT/FWAIT instruction.
•
If the EM flag is set, the setting of the TS flag has no affect on the execution of x87
FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instructions.
Table 2-2 shows the actions taken when the processor encounters an x87 FPU instruction based on the
settings of the TS, EM, and MP flags. Table 12-1 and 13-1 show the actions taken when the processor
encounters an MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instruction.
The processor does not automatically save the context of the x87 FPU, XMM, and MXCSR registers on a
task switch. Instead, it sets the TS flag, which causes the processor to raise an #NM exception whenever
it encounters an x87 FPU/MMX/SSE /SSE2/SSE3/SSSE3/SSE4 instruction in the instruction stream for the
new task (with the exception of the instructions listed above).
The fault handler for the #NM exception can then be used to clear the TS flag (with the CLTS instruction) and save
the context of the x87 FPU, XMM, and MXCSR registers. If the task never encounters an x87
FPU/MMX/SSE/SSE2/SSE3//SSSE3/SSE4 instruction; the x87 FPU/MMX/SSE/SSE2/ SSE3/SSSE3/SSE4 context is
never saved.
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SYSTEM ARCHITECTURE OVERVIEW
Table 2-2. Action Taken By x87 FPU Instructions for Different Combinations of EM, MP, and TS
CR0 Flags
EM
EM
MP
x87 FPU Instruction Type
TS
Floating-Point
WAIT/FWAIT
0
0
0
Execute
Execute.
0
0
1
#NM Exception
Execute.
0
1
0
Execute
Execute.
0
1
1
#NM Exception
#NM exception.
1
0
0
#NM Exception
Execute.
1
0
1
#NM Exception
Execute.
1
1
0
#NM Exception
Execute.
1
1
1
#NM Exception
#NM exception.
Emulation (bit 2 of CR0) — Indicates that the processor does not have an internal or external x87 FPU
when set; indicates an x87 FPU is present when clear. This flag also affects the execution of
MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instructions.
When the EM flag is set, execution of an x87 FPU instruction generates a device-not-available exception
(#NM). This flag must be set when the processor does not have an internal x87 FPU or is not connected to
an external math coprocessor. Setting this flag forces all floating-point instructions to be handled by software emulation. Table 9-2 shows the recommended setting of this flag, depending on the IA-32 processor
and x87 FPU or math coprocessor present in the system. Table 2-2 shows the interaction of the EM, MP, and
TS flags.
Also, when the EM flag is set, execution of an MMX instruction causes an invalid-opcode exception (#UD)
to be generated (see Table 12-1). Thus, if an IA-32 or Intel 64 processor incorporates MMX technology, the
EM flag must be set to 0 to enable execution of MMX instructions.
Similarly for SSE/SSE2/SSE3/SSSE3/SSE4 extensions, when the EM flag is set, execution of most
SSE/SSE2/SSE3/SSSE3/SSE4 instructions causes an invalid opcode exception (#UD) to be generated (see
Table 13-1). If an IA-32 or Intel 64 processor incorporates the SSE/SSE2/SSE3/SSSE3/SSE4 extensions,
the EM flag must be set to 0 to enable execution of these extensions. SSE/SSE2/SSE3/SSSE3/SSE4
instructions not affected by the EM flag include: PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE, MOVNTI,
CLFLUSH, CRC32, and POPCNT.
MP
Monitor Coprocessor (bit 1 of CR0). — Controls the interaction of the WAIT (or FWAIT) instruction with
the TS flag (bit 3 of CR0). If the MP flag is set, a WAIT instruction generates a device-not-available exception
(#NM) if the TS flag is also set. If the MP flag is clear, the WAIT instruction ignores the setting of the TS flag.
Table 9-2 shows the recommended setting of this flag, depending on the IA-32 processor and x87 FPU or
math coprocessor present in the system. Table 2-2 shows the interaction of the MP, EM, and TS flags.
PE
Protection Enable (bit 0 of CR0) — Enables protected mode when set; enables real-address mode when
clear. This flag does not enable paging directly. It only enables segment-level protection. To enable paging,
both the PE and PG flags must be set.
See also: Section 9.9, “Mode Switching.”
PCD
Page-level Cache Disable (bit 4 of CR3) — Controls the memory type used to access the first paging
structure of the current paging-structure hierarchy. See Section 4.9, “Paging and Memory Typing”. This bit
is not used if paging is disabled, with PAE paging, or with IA-32e paging if CR4.PCIDE=1.
PWT
Page-level Write-Through (bit 3 of CR3) — Controls the memory type used to access the first paging
structure of the current paging-structure hierarchy. See Section 4.9, “Paging and Memory Typing”. This bit
is not used if paging is disabled, with PAE paging, or with IA-32e paging if CR4.PCIDE=1.
VME
Virtual-8086 Mode Extensions (bit 0 of CR4) — Enables interrupt- and exception-handling extensions
in virtual-8086 mode when set; disables the extensions when clear. Use of the virtual mode extensions can
improve the performance of virtual-8086 applications by eliminating the overhead of calling the virtual8086 monitor to handle interrupts and exceptions that occur while executing an 8086 program and,
instead, redirecting the interrupts and exceptions back to the 8086 program’s handlers. It also provides
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SYSTEM ARCHITECTURE OVERVIEW
hardware support for a virtual interrupt flag (VIF) to improve reliability of running 8086 programs in multitasking and multiple-processor environments.
See also: Section 20.3, “Interrupt and Exception Handling in Virtual-8086 Mode.”
PVI
Protected-Mode Virtual Interrupts (bit 1 of CR4) — Enables hardware support for a virtual interrupt
flag (VIF) in protected mode when set; disables the VIF flag in protected mode when clear.
See also: Section 20.4, “Protected-Mode Virtual Interrupts.”
TSD
Time Stamp Disable (bit 2 of CR4) — Restricts the execution of the RDTSC instruction to procedures
running at privilege level 0 when set; allows RDTSC instruction to be executed at any privilege level when
clear. This bit also applies to the RDTSCP instruction if supported (if CPUID.80000001H:EDX[27] = 1).
DE
Debugging Extensions (bit 3 of CR4) — References to debug registers DR4 and DR5 cause an undefined opcode (#UD) exception to be generated when set; when clear, processor aliases references to registers DR4 and DR5 for compatibility with software written to run on earlier IA-32 processors.
See also: Section 17.2.2, “Debug Registers DR4 and DR5.”
PSE
Page Size Extensions (bit 4 of CR4) — Enables 4-MByte pages with 32-bit paging when set; restricts
32-bit paging to pages to 4 KBytes when clear.
See also: Section 4.3, “32-Bit Paging.”
PAE
Physical Address Extension (bit 5 of CR4) — When set, enables paging to produce physical addresses
with more than 32 bits. When clear, restricts physical addresses to 32 bits. PAE must be set before entering
IA-32e mode.
See also: Chapter 4, “Paging.”
MCE
Machine-Check Enable (bit 6 of CR4) — Enables the machine-check exception when set; disables the
machine-check exception when clear.
See also: Chapter 15, “Machine-Check Architecture.”
PGE
Page Global Enable (bit 7 of CR4) — (Introduced in the P6 family processors.) Enables the global page
feature when set; disables the global page feature when clear. The global page feature allows frequently
used or shared pages to be marked as global to all users (done with the global flag, bit 8, in a page-directory or page-table entry). Global pages are not flushed from the translation-lookaside buffer (TLB) on a
task switch or a write to register CR3.
When enabling the global page feature, paging must be enabled (by setting the PG flag in control register
CR0) before the PGE flag is set. Reversing this sequence may affect program correctness, and processor
performance will be impacted.
See also: Section 4.10, “Caching Translation Information.”
PCE
Performance-Monitoring Counter Enable (bit 8 of CR4) — Enables execution of the RDPMC instruction for programs or procedures running at any protection level when set; RDPMC instruction can be
executed only at protection level 0 when clear.
OSFXSR
Operating System Support for FXSAVE and FXRSTOR instructions (bit 9 of CR4) — When set, this
flag: (1) indicates to software that the operating system supports the use of the FXSAVE and FXRSTOR
instructions, (2) enables the FXSAVE and FXRSTOR instructions to save and restore the contents of the
XMM and MXCSR registers along with the contents of the x87 FPU and MMX registers, and (3) enables the
processor to execute SSE/SSE2/SSE3/SSSE3/SSE4 instructions, with the exception of the PAUSE,
PREFETCHh, SFENCE, LFENCE, MFENCE, MOVNTI, CLFLUSH, CRC32, and POPCNT.
If this flag is clear, the FXSAVE and FXRSTOR instructions will save and restore the contents of the x87 FPU
and MMX instructions, but they may not save and restore the contents of the XMM and MXCSR registers.
Also, the processor will generate an invalid opcode exception (#UD) if it attempts to execute any
SSE/SSE2/SSE3 instruction, with the exception of PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE,
MOVNTI, CLFLUSH, CRC32, and POPCNT. The operating system or executive must explicitly set this flag.
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SYSTEM ARCHITECTURE OVERVIEW
NOTE
CPUID feature flags FXSR indicates availability of the FXSAVE/FXRSTOR instructions. The OSFXSR
bit provides operating system software with a means of enabling FXSAVE/FXRSTOR to save/restore
the contents of the X87 FPU, XMM and MXCSR registers. Consequently OSFXSR bit indicates that
the operating system provides context switch support for SSE/SSE2/SSE3/SSSE3/SSE4.
OSXMMEXCPT
Operating System Support for Unmasked SIMD Floating-Point Exceptions (bit 10 of CR4) —
When set, indicates that the operating system supports the handling of unmasked SIMD floating-point
exceptions through an exception handler that is invoked when a SIMD floating-point exception (#XF) is
generated. SIMD floating-point exceptions are only generated by SSE/SSE2/SSE3/SSE4.1 SIMD floatingpoint instructions.
The operating system or executive must explicitly set this flag. If this flag is not set, the processor will
generate an invalid opcode exception (#UD) whenever it detects an unmasked SIMD floating-point exception.
VMXE
VMX-Enable Bit (bit 13 of CR4) — Enables VMX operation when set. See Chapter 23, “Introduction to
Virtual-Machine Extensions.”
SMXE
SMX-Enable Bit (bit 14 of CR4) — Enables SMX operation when set. See Chapter 30, “VMX Instruction
Reference” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3C.
FSGSBASE
FSGSBASE-Enable Bit (bit 16 of CR4) — Enables the instructions RDFSBASE, RDGSBASE, WRFSBASE,
and WRGSBASE.
PCIDE
PCID-Enable Bit (bit 17 of CR4) — Enables process-context identifiers (PCIDs) when set. See Section
4.10.1, “Process-Context Identifiers (PCIDs)”. Can be set only in IA-32e mode (if IA32_EFER.LMA = 1).
OSXSAVE
XSAVE and Processor Extended States-Enable Bit (bit 18 of CR4) — When set, this flag: (1) indicates (via CPUID.01H:ECX.OSXSAVE[bit 27]) that the operating system supports the use of the XGETBV,
XSAVE and XRSTOR instructions by general software; (2) enables the XSAVE and XRSTOR instructions to
save and restore the x87 FPU state (including MMX registers), the SSE state (XMM registers and MXCSR),
along with other processor extended states enabled in XCR0; (3) enables the processor to execute XGETBV
and XSETBV instructions in order to read and write XCR0. See Section 2.6 and Chapter 13, “System
Programming for Instruction Set Extensions and Processor Extended States”.
SMEP
SMEP-Enable Bit (bit 20 of CR4) — Enables supervisor-mode execution prevention (SMEP) when set.
See Section 4.6, “Access Rights”.
TPL
Task Priority Level (bit 3:0 of CR8) — This sets the threshold value corresponding to the highestpriority interrupt to be blocked. A value of 0 means all interrupts are enabled. This field is available in 64bit mode. A value of 15 means all interrupts will be disabled.
2.5.1
CPUID Qualification of Control Register Flags
Not all flags in control register CR4 are implemented on all processors. With the exception of the PCE flag, they can
be qualified with the CPUID instruction to determine if they are implemented on the processor before they are
used.
The CR8 register is available on processors that support Intel 64 architecture.
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SYSTEM ARCHITECTURE OVERVIEW
2.6
EXTENDED CONTROL REGISTERS (INCLUDING XCR0)
If CPUID.01H:ECX.XSAVE[bit 26] is 1, the processor supports one or more extended control registers (XCRs).
Currently, the only such register defined is XCR0. This register specifies the set of processor states that the operating system enables on that processor, e.g. x87 FPU state, SSE state, AVX state, and other processor extended
states that Intel 64 architecture may introduce in the future. The OS programs XCR0 to reflect the features it
supports.
63
2 1 0
1
Reserved for XCR0 bit vector expansion
Reserved / Future processor extended states
AVX state
SSE state
x87 FPU/MMX state (must be 1)
Reserved (must be 0)
Figure 2-8. XCR0
Software can access XCR0 only if CR4.OSXSAVE[bit 18] = 1. (This bit is also readable as
CPUID.01H:ECX.OSXSAVE[bit 27].) The layout of XCR0 is architected to allow software to use CPUID leaf function
0DH to enumerate the set of bits that the processor supports in XCR0 (see CPUID instruction in Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 2A). Each processor state (X87 FPU state, SSE state,
AVX state, or a future processor extended state) is represented by a bit in XCR0. The OS can enable future
processor extended states in a forward manner by specifying the appropriate bit mask value using the XSETBV
instruction according to the results of the CPUID leaf 0DH.
With the exception of bit 63, each bit in XCR0 corresponds to a subset of the processor states. XCR0 thus provides
space for up to 63 sets of processor state extensions. Bit 63 of XCR0 is reserved for future expansion and will not
represent a processor extended state.
Currently, XCR0 has three processor states defined, with up to 61 bits reserved for future processor extended
states:
•
•
XCR0.X87 (bit 0): This bit 0 must be 1. An attempt to write 0 to this bit causes a #GP exception.
•
XCR0.AVX (bit 2): If 1, AVX instructions can be executed and XSAVE, XSAVEOPT, and XRSTOR can be used to
manage the upper halves of the YMM registers (YMM0-YMM15 in 64-bit mode; otherwise YMM0-YMM7).
XCR0.SSE (bit 1): If 1, XSAVE, XSAVEOPT, and XRSTOR can be used to manage MXCSR and XMM registers
(XMM0-XMM15 in 64-bit mode; otherwise XMM0-XMM7).
Any attempt to set a reserved bit (as determined by the contents of EAX and EDX after executing CPUID with
EAX=0DH, ECX= 0H) in XCR0 for a given processor will result in a #GP exception. An attempt to write 0 to
XCR0.x87 (bit 0) will result in a #GP exception. An attempt to write 0 to XCR0.SSE (bit 1) and 1 to XCR0.AVX (bit
2) also results in a #GP exception.
If a bit in XCR0 is 1, software can use the XSAVE instruction to save the corresponding processor state to memory
(see XSAVE instruction in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2B).
After reset, all bits (except bit 0) in XCR0 are cleared to zero, XCR0[0] is set to 1.
2.7
SYSTEM INSTRUCTION SUMMARY
System instructions handle system-level functions such as loading system registers, managing the cache,
managing interrupts, or setting up the debug registers. Many of these instructions can be executed only by oper-
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SYSTEM ARCHITECTURE OVERVIEW
ating-system or executive procedures (that is, procedures running at privilege level 0). Others can be executed at
any privilege level and are thus available to application programs.
Table 2-3 lists the system instructions and indicates whether they are available and useful for application programs.
These instructions are described in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes
2A, 2B & 2C.
Table 2-3. Summary of System Instructions
Useful to
Application?
Protected from
Application?
Instruction
Description
LLDT
Load LDT Register
No
Yes
SLDT
Store LDT Register
No
No
LGDT
Load GDT Register
No
Yes
SGDT
Store GDT Register
No
No
LTR
Load Task Register
No
Yes
STR
Store Task Register
No
No
LIDT
Load IDT Register
No
Yes
SIDT
Store IDT Register
No
No
MOV CRn
Load and store control registers
No
Yes
SMSW
Store MSW
Yes
No
LMSW
Load MSW
No
Yes
CLTS
Clear TS flag in CR0
No
Yes
ARPL
Adjust RPL
LAR
Load Access Rights
Yes
No
LSL
Load Segment Limit
Yes
No
VERR
Verify for Reading
Yes
No
VERW
Verify for Writing
Yes
No
MOV DRn
Load and store debug registers
No
Yes
INVD
Invalidate cache, no writeback
No
Yes
WBINVD
Invalidate cache, with writeback
No
Yes
INVLPG
Invalidate TLB entry
No
Yes
Yes
1, 5
No
HLT
Halt Processor
No
Yes
LOCK (Prefix)
Bus Lock
Yes
No
RSM
Return from system management mode
No
Yes
RDMSR3
Read Model-Specific Registers
No
Yes
WRMSR3
Write Model-Specific Registers
No
Yes
RDPMC4
Read Performance-Monitoring Counter
Yes
Yes2
RDTSC3
Read Time-Stamp Counter
Yes
Yes2
RDTSCP7
Read Serialized Time-Stamp Counter
Yes
Yes2
XGETBV
Return the state of XCR0
Yes
No
XSETBV
Enable one or more processor extended states
No6
Yes
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SYSTEM ARCHITECTURE OVERVIEW
Table 2-3. Summary of System Instructions (Contd.)
Instruction
Description
Useful to
Application?
Protected from
Application?
NOTES:
1. Useful to application programs running at a CPL of 1 or 2.
2. The TSD and PCE flags in control register CR4 control access to these instructions by application programs running at a CPL of 3.
3. These instructions were introduced into the IA-32 Architecture with the Pentium processor.
4. This instruction was introduced into the IA-32 Architecture with the Pentium Pro processor and the Pentium processor with MMX
technology.
5. This instruction is not supported in 64-bit mode.
6. Application uses XGETBV to query which set of processor extended states are enabled.
7. RDTSCP is introduced in Intel Core i7 processor.
2.7.1
Loading and Storing System Registers
The GDTR, LDTR, IDTR, and TR registers each have a load and store instruction for loading data into and storing
data from the register:
•
•
•
•
•
LGDT (Load GDTR Register) — Loads the GDT base address and limit from memory into the GDTR register.
•
SLDT (Store LDT Register) — Stores the LDT segment selector from the LDTR register into memory or a
general-purpose register.
•
LTR (Load Task Register) — Loads segment selector and segment descriptor for a TSS from memory into the
task register. (The segment selector operand can also be located in a general-purpose register.)
•
STR (Store Task Register) — Stores the segment selector for the current task TSS from the task register into
memory or a general-purpose register.
SGDT (Store GDTR Register) — Stores the GDT base address and limit from the GDTR register into memory.
LIDT (Load IDTR Register) — Loads the IDT base address and limit from memory into the IDTR register.
SIDT (Load IDTR Register — Stores the IDT base address and limit from the IDTR register into memory.
LLDT (Load LDT Register) — Loads the LDT segment selector and segment descriptor from memory into the
LDTR. (The segment selector operand can also be located in a general-purpose register.)
The LMSW (load machine status word) and SMSW (store machine status word) instructions operate on bits 0
through 15 of control register CR0. These instructions are provided for compatibility with the 16-bit Intel 286
processor. Programs written to run on 32-bit IA-32 processors should not use these instructions. Instead, they
should access the control register CR0 using the MOV instruction.
The CLTS (clear TS flag in CR0) instruction is provided for use in handling a device-not-available exception (#NM)
that occurs when the processor attempts to execute a floating-point instruction when the TS flag is set. This
instruction allows the TS flag to be cleared after the x87 FPU context has been saved, preventing further #NM
exceptions. See Section 2.5, “Control Registers,” for more information on the TS flag.
The control registers (CR0, CR1, CR2, CR3, CR4, and CR8) are loaded using the MOV instruction. The instruction
loads a control register from a general-purpose register or stores the content of a control register in a generalpurpose register.
2.7.2
Verifying of Access Privileges
The processor provides several instructions for examining segment selectors and segment descriptors to determine if access to their associated segments is allowed. These instructions duplicate some of the automatic access
rights and type checking done by the processor, thus allowing operating-system or executive software to prevent
exceptions from being generated.
The ARPL (adjust RPL) instruction adjusts the RPL (requestor privilege level) of a segment selector to match that
of the program or procedure that supplied the segment selector. See Section 5.10.4, “Checking Caller Access Priv-
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SYSTEM ARCHITECTURE OVERVIEW
ileges (ARPL Instruction),” for a detailed explanation of the function and use of this instruction. Note that ARPL is
not supported in 64-bit mode.
The LAR (load access rights) instruction verifies the accessibility of a specified segment and loads access rights
information from the segment’s segment descriptor into a general-purpose register. Software can then examine
the access rights to determine if the segment type is compatible with its intended use. See Section 5.10.1,
“Checking Access Rights (LAR Instruction),” for a detailed explanation of the function and use of this instruction.
The LSL (load segment limit) instruction verifies the accessibility of a specified segment and loads the segment
limit from the segment’s segment descriptor into a general-purpose register. Software can then compare the
segment limit with an offset into the segment to determine whether the offset lies within the segment. See Section
5.10.3, “Checking That the Pointer Offset Is Within Limits (LSL Instruction),” for a detailed explanation of the function and use of this instruction.
The VERR (verify for reading) and VERW (verify for writing) instructions verify if a selected segment is readable or
writable, respectively, at a given CPL. See Section 5.10.2, “Checking Read/Write Rights (VERR and VERW Instructions),” for a detailed explanation of the function and use of this instruction.
2.7.3
Loading and Storing Debug Registers
Internal debugging facilities in the processor are controlled by a set of 8 debug registers (DR0-DR7). The MOV
instruction allows setup data to be loaded to and stored from these registers.
On processors that support Intel 64 architecture, debug registers DR0-DR7 are 64 bits. In 32-bit modes and
compatibility mode, writes to a debug register fill the upper 32 bits with zeros. Reads return the lower 32 bits. In
64-bit mode, the upper 32 bits of DR6-DR7 are reserved and must be written with zeros. Writing one to any of the
upper 32 bits causes an exception, #GP(0).
In 64-bit mode, MOV DRn instructions read or write all 64 bits of a debug register (operand-size prefixes are
ignored). All 64 bits of DR0-DR3 are writable by software. However, MOV DRn instructions do not check that
addresses written to DR0-DR3 are in the limits of the implementation. Address matching is supported only on valid
addresses generated by the processor implementation.
2.7.4
Invalidating Caches and TLBs
The processor provides several instructions for use in explicitly invalidating its caches and TLB entries. The INVD
(invalidate cache with no writeback) instruction invalidates all data and instruction entries in the internal caches
and sends a signal to the external caches indicating that they should be also be invalidated.
The WBINVD (invalidate cache with writeback) instruction performs the same function as the INVD instruction,
except that it writes back modified lines in its internal caches to memory before it invalidates the caches. After
invalidating the caches local to the executing logical processor or processor core, WBINVD signals caches higher in
the cache hierarchy (caches shared with the invalidating logical processor or core) to write back any data they have
in modified state, at the time of instruction execution and to invalidate their contents.
Note, non-shared caches may not be written back nor invalidated. In Figure 2-9 below, if code executing on either
LP0 or LP1 were to execute a WBINVD, the shared L1 and L2 for LP0/LP1 will be written back and invalidated as do
the shared L3. However, the L1 and L2 caches not shared with LP0 and LP1 will not be written back nor invalidated.
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SYSTEM ARCHITECTURE OVERVIEW
Logical Processors
L1 & L2 Cache
LP0
LP1
LP2
LP3
LP4
LP5
LP6
Not Written back and
not Invalidated
LP7
Written back
& Invalidated
Execution Engine
L3 Cache
Written back and Invalidated
Uncore
QPI
DDR3
Figure 2-9. WBINVD Invalidation of Shared and Non-Shared Cache Hierarchy
The INVLPG (invalidate TLB entry) instruction invalidates (flushes) the TLB entry for a specified page.
2.7.5
Controlling the Processor
The HLT (halt processor) instruction stops the processor until an enabled interrupt (such as NMI or SMI, which are
normally enabled), a debug exception, the BINIT# signal, the INIT# signal, or the RESET# signal is received. The
processor generates a special bus cycle to indicate that the halt mode has been entered.
Hardware may respond to this signal in a number of ways. An indicator light on the front panel may be turned on.
An NMI interrupt for recording diagnostic information may be generated. Reset initialization may be invoked (note
that the BINIT# pin was introduced with the Pentium Pro processor). If any non-wake events are pending during
shutdown, they will be handled after the wake event from shutdown is processed (for example, A20M# interrupts).
The LOCK prefix invokes a locked (atomic) read-modify-write operation when modifying a memory operand. This
mechanism is used to allow reliable communications between processors in multiprocessor systems, as described
below:
•
In the Pentium processor and earlier IA-32 processors, the LOCK prefix causes the processor to assert the
LOCK# signal during the instruction. This always causes an explicit bus lock to occur.
•
In the Pentium 4, Intel Xeon, and P6 family processors, the locking operation is handled with either a cache lock
or bus lock. If a memory access is cacheable and affects only a single cache line, a cache lock is invoked and
the system bus and the actual memory location in system memory are not locked during the operation. Here,
other Pentium 4, Intel Xeon, or P6 family processors on the bus write-back any modified data and invalidate
their caches as necessary to maintain system memory coherency. If the memory access is not cacheable
and/or it crosses a cache line boundary, the processor’s LOCK# signal is asserted and the processor does not
respond to requests for bus control during the locked operation.
The RSM (return from SMM) instruction restores the processor (from a context dump) to the state it was in prior to
an system management mode (SMM) interrupt.
2.7.6
Reading Performance-Monitoring and Time-Stamp Counters
The RDPMC (read performance-monitoring counter) and RDTSC (read time-stamp counter) instructions allow
application programs to read the processor’s performance-monitoring and time-stamp counters, respectively.
Processors based on Intel NetBurst® microarchitecture have eighteen 40-bit performance-monitoring counters; P6
family processors have two 40-bit counters. Intel® Atom™ processors and most of the processors based on the
Intel Core microarchitecture support two types of performance monitoring counters: two programmable perfor-
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SYSTEM ARCHITECTURE OVERVIEW
mance counters similar to those available in the P6 family, and three fixed-function performance monitoring
counters.
The programmable performance counters can support counting either the occurrence or duration of events. Events
that can be monitored on programmable counters generally are model specific (except for architectural performance events enumerated by CPUID leaf 0AH); they may include the number of instructions decoded, interrupts
received, or the number of cache loads. Individual counters can be set up to monitor different events. Use the
system instruction WRMSR to set up values in IA32_PERFEVTSEL0/1 (for Intel Atom, Intel Core 2, Intel Core Duo,
and Intel Pentium M processors), in one of the 45 ESCRs and one of the 18 CCCR MSRs (for Pentium 4 and Intel
Xeon processors); or in the PerfEvtSel0 or the PerfEvtSel1 MSR (for the P6 family processors). The RDPMC instruction loads the current count from the selected counter into the EDX:EAX registers.
Fixed-function performance counters record only specific events that are defined in Chapter 23, “Introduction to
Virtual-Machine Extensions”, and the width/number of fixed-function counters are enumerated by CPUID leaf 0AH.
The time-stamp counter is a model-specific 64-bit counter that is reset to zero each time the processor is reset. If
not reset, the counter will increment ~9.5 x 1016 times per year when the processor is operating at a clock rate
of 3GHz. At this clock frequency, it would take over 190 years for the counter to wrap around. The RDTSC
instruction loads the current count of the time-stamp counter into the EDX:EAX registers.
See Section 18.1, “Performance Monitoring Overview,” and Section 17.13, “Time-Stamp Counter,” for more information about the performance monitoring and time-stamp counters.
The RDTSC instruction was introduced into the IA-32 architecture with the Pentium processor. The RDPMC instruction was introduced into the IA-32 architecture with the Pentium Pro processor and the Pentium processor with
MMX technology. Earlier Pentium processors have two performance-monitoring counters, but they can be read only
with the RDMSR instruction, and only at privilege level 0.
2.7.6.1
Reading Counters in 64-Bit Mode
In 64-bit mode, RDTSC operates the same as in protected mode. The count in the time-stamp counter is stored in
EDX:EAX (or RDX[31:0]:RAX[31:0] with RDX[63:32]:RAX[63:32] cleared).
RDPMC requires an index to specify the offset of the performance-monitoring counter. In 64-bit mode for Pentium
4 or Intel Xeon processor families, the index is specified in ECX[30:0]. The current count of the performance-monitoring counter is stored in EDX:EAX (or RDX[31:0]:RAX[31:0] with RDX[63:32]:RAX[63:32] cleared).
2.7.7
Reading and Writing Model-Specific Registers
The RDMSR (read model-specific register) and WRMSR (write model-specific register) instructions allow a
processor’s 64-bit model-specific registers (MSRs) to be read and written, respectively. The MSR to be read or
written is specified by the value in the ECX register.
RDMSR reads the value from the specified MSR to the EDX:EAX registers; WRMSR writes the value in the EDX:EAX
registers to the specified MSR. RDMSR and WRMSR were introduced into the IA-32 architecture with the Pentium
processor.
See Section 9.4, “Model-Specific Registers (MSRs),” for more information.
2.7.7.1
Reading and Writing Model-Specific Registers in 64-Bit Mode
RDMSR and WRMSR require an index to specify the address of an MSR. In 64-bit mode, the index is 32 bits; it is
specified using ECX.
2.7.8
Enabling Processor Extended States
The XSETBV instruction is required to enable OS support of individual processor extended states in XCR0 (see
Section 2.6).
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CHAPTER 3
PROTECTED-MODE MEMORY MANAGEMENT
This chapter describes the Intel 64 and IA-32 architecture’s protected-mode memory management facilities,
including the physical memory requirements, segmentation mechanism, and paging mechanism.
See also: Chapter 5, “Protection” (for a description of the processor’s protection mechanism) and Chapter 20,
“8086 Emulation” (for a description of memory addressing protection in real-address and virtual-8086 modes).
3.1
MEMORY MANAGEMENT OVERVIEW
The memory management facilities of the IA-32 architecture are divided into two parts: segmentation and paging.
Segmentation provides a mechanism of isolating individual code, data, and stack modules so that multiple
programs (or tasks) can run on the same processor without interfering with one another. Paging provides a mechanism for implementing a conventional demand-paged, virtual-memory system where sections of a program’s
execution environment are mapped into physical memory as needed. Paging can also be used to provide isolation
between multiple tasks. When operating in protected mode, some form of segmentation must be used. There is
no mode bit to disable segmentation. The use of paging, however, is optional.
These two mechanisms (segmentation and paging) can be configured to support simple single-program (or singletask) systems, multitasking systems, or multiple-processor systems that used shared memory.
As shown in Figure 3-1, segmentation provides a mechanism for dividing the processor’s addressable memory
space (called the linear address space) into smaller protected address spaces called segments. Segments can
be used to hold the code, data, and stack for a program or to hold system data structures (such as a TSS or LDT).
If more than one program (or task) is running on a processor, each program can be assigned its own set of
segments. The processor then enforces the boundaries between these segments and insures that one program
does not interfere with the execution of another program by writing into the other program’s segments. The
segmentation mechanism also allows typing of segments so that the operations that may be performed on a particular type of segment can be restricted.
All the segments in a system are contained in the processor’s linear address space. To locate a byte in a particular
segment, a logical address (also called a far pointer) must be provided. A logical address consists of a segment
selector and an offset. The segment selector is a unique identifier for a segment. Among other things it provides an
offset into a descriptor table (such as the global descriptor table, GDT) to a data structure called a segment
descriptor. Each segment has a segment descriptor, which specifies the size of the segment, the access rights and
privilege level for the segment, the segment type, and the location of the first byte of the segment in the linear
address space (called the base address of the segment). The offset part of the logical address is added to the base
address for the segment to locate a byte within the segment. The base address plus the offset thus forms a linear
address in the processor’s linear address space.
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Logical Address
(or Far Pointer)
Segment
Selector
Offset
Linear Address
Space
Global Descriptor
Table (GDT)
Dir
Linear Address
Table
Offset
Segment
Page Table
Segment
Descriptor
Page Directory
Lin. Addr.
Physical
Address
Space
Page
Phy. Addr.
Entry
Entry
Segment
Base Address
Page
Segmentation
Paging
Figure 3-1. Segmentation and Paging
If paging is not used, the linear address space of the processor is mapped directly into the physical address space
of processor. The physical address space is defined as the range of addresses that the processor can generate on
its address bus.
Because multitasking computing systems commonly define a linear address space much larger than it is economically feasible to contain all at once in physical memory, some method of “virtualizing” the linear address space is
needed. This virtualization of the linear address space is handled through the processor’s paging mechanism.
Paging supports a “virtual memory” environment where a large linear address space is simulated with a small
amount of physical memory (RAM and ROM) and some disk storage. When using paging, each segment is divided
into pages (typically 4 KBytes each in size), which are stored either in physical memory or on the disk. The operating system or executive maintains a page directory and a set of page tables to keep track of the pages. When a
program (or task) attempts to access an address location in the linear address space, the processor uses the page
directory and page tables to translate the linear address into a physical address and then performs the requested
operation (read or write) on the memory location.
If the page being accessed is not currently in physical memory, the processor interrupts execution of the program
(by generating a page-fault exception). The operating system or executive then reads the page into physical
memory from the disk and continues executing the program.
When paging is implemented properly in the operating-system or executive, the swapping of pages between physical memory and the disk is transparent to the correct execution of a program. Even programs written for 16-bit IA32 processors can be paged (transparently) when they are run in virtual-8086 mode.
3.2
USING SEGMENTS
The segmentation mechanism supported by the IA-32 architecture can be used to implement a wide variety of
system designs. These designs range from flat models that make only minimal use of segmentation to protect
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programs to multi-segmented models that employ segmentation to create a robust operating environment in
which multiple programs and tasks can be executed reliably.
The following sections give several examples of how segmentation can be employed in a system to improve
memory management performance and reliability.
3.2.1
Basic Flat Model
The simplest memory model for a system is the basic “flat model,” in which the operating system and application
programs have access to a continuous, unsegmented address space. To the greatest extent possible, this basic flat
model hides the segmentation mechanism of the architecture from both the system designer and the application
programmer.
To implement a basic flat memory model with the IA-32 architecture, at least two segment descriptors must be
created, one for referencing a code segment and one for referencing a data segment (see Figure 3-2). Both of
these segments, however, are mapped to the entire linear address space: that is, both segment descriptors have
the same base address value of 0 and the same segment limit of 4 GBytes. By setting the segment limit to 4
GBytes, the segmentation mechanism is kept from generating exceptions for out of limit memory references, even
if no physical memory resides at a particular address. ROM (EPROM) is generally located at the top of the physical
address space, because the processor begins execution at FFFF_FFF0H. RAM (DRAM) is placed at the bottom of the
address space because the initial base address for the DS data segment after reset initialization is 0.
3.2.2
Protected Flat Model
The protected flat model is similar to the basic flat model, except the segment limits are set to include only the
range of addresses for which physical memory actually exists (see Figure 3-3). A general-protection exception
(#GP) is then generated on any attempt to access nonexistent memory. This model provides a minimum level of
hardware protection against some kinds of program bugs.
Linear Address Space
(or Physical Memory)
Segment
Registers
CS
Code
Code- and Data-Segment
Descriptors
SS
DS
ES
Access
Limit
Base Address
FFFFFFFFH
Not Present
Data and
Stack
0
FS
GS
Figure 3-2. Flat Model
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Segment
Registers
Segment
Descriptors
Linear Address Space
(or Physical Memory)
Access
Limit
Base Address
Code
FFFFFFFFH
CS
Not Present
ES
SS
DS
FS
Memory I/O
Access
Limit
Base Address
Data and
Stack
GS
0
Figure 3-3. Protected Flat Model
More complexity can be added to this protected flat model to provide more protection. For example, for the paging
mechanism to provide isolation between user and supervisor code and data, four segments need to be defined:
code and data segments at privilege level 3 for the user, and code and data segments at privilege level 0 for the
supervisor. Usually these segments all overlay each other and start at address 0 in the linear address space. This
flat segmentation model along with a simple paging structure can protect the operating system from applications,
and by adding a separate paging structure for each task or process, it can also protect applications from each other.
Similar designs are used by several popular multitasking operating systems.
3.2.3
Multi-Segment Model
A multi-segment model (such as the one shown in Figure 3-4) uses the full capabilities of the segmentation mechanism to provided hardware enforced protection of code, data structures, and programs and tasks. Here, each
program (or task) is given its own table of segment descriptors and its own segments. The segments can be
completely private to their assigned programs or shared among programs. Access to all segments and to the
execution environments of individual programs running on the system is controlled by hardware.
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Segment
Registers
Segment
Descriptors
Linear Address Space
(or Physical Memory)
CS
Access
Limit
Base Address
Stack
SS
Access
Limit
Base Address
DS
Access
Limit
Base Address
ES
Access
Limit
Base Address
FS
Access
Limit
Base Address
GS
Access
Limit
Base Address
Access
Limit
Base Address
Code
Data
Data
Data
Access
Limit
Base Address
Access
Limit
Base Address
Data
Access
Limit
Base Address
Figure 3-4. Multi-Segment Model
Access checks can be used to protect not only against referencing an address outside the limit of a segment, but
also against performing disallowed operations in certain segments. For example, since code segments are designated as read-only segments, hardware can be used to prevent writes into code segments. The access rights information created for segments can also be used to set up protection rings or levels. Protection levels can be used to
protect operating-system procedures from unauthorized access by application programs.
3.2.4
Segmentation in IA-32e Mode
In IA-32e mode of Intel 64 architecture, the effects of segmentation depend on whether the processor is running
in compatibility mode or 64-bit mode. In compatibility mode, segmentation functions just as it does using legacy
16-bit or 32-bit protected mode semantics.
In 64-bit mode, segmentation is generally (but not completely) disabled, creating a flat 64-bit linear-address
space. The processor treats the segment base of CS, DS, ES, SS as zero, creating a linear address that is equal to
the effective address. The FS and GS segments are exceptions. These segment registers (which hold the segment
base) can be used as an additional base registers in linear address calculations. They facilitate addressing local
data and certain operating system data structures.
Note that the processor does not perform segment limit checks at runtime in 64-bit mode.
3.2.5
Paging and Segmentation
Paging can be used with any of the segmentation models described in Figures 3-2, 3-3, and 3-4. The processor’s
paging mechanism divides the linear address space (into which segments are mapped) into pages (as shown in
Figure 3-1). These linear-address-space pages are then mapped to pages in the physical address space. The
paging mechanism offers several page-level protection facilities that can be used with or instead of the segment-
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protection facilities. For example, it lets read-write protection be enforced on a page-by-page basis. The paging
mechanism also provides two-level user-supervisor protection that can also be specified on a page-by-page basis.
3.3
PHYSICAL ADDRESS SPACE
In protected mode, the IA-32 architecture provides a normal physical address space of 4 GBytes (232 bytes). This
is the address space that the processor can address on its address bus. This address space is flat (unsegmented),
with addresses ranging continuously from 0 to FFFFFFFFH. This physical address space can be mapped to readwrite memory, read-only memory, and memory mapped I/O. The memory mapping facilities described in this
chapter can be used to divide this physical memory up into segments and/or pages.
Starting with the Pentium Pro processor, the IA-32 architecture also supports an extension of the physical address
space to 236 bytes (64 GBytes); with a maximum physical address of FFFFFFFFFH. This extension is invoked in
either of two ways:
•
•
Using the physical address extension (PAE) flag, located in bit 5 of control register CR4.
Using the 36-bit page size extension (PSE-36) feature (introduced in the Pentium III processors).
Physical address support has since been extended beyond 36 bits. See Chapter 4, “Paging” for more information
about 36-bit physical addressing.
3.3.1
Intel® 64 Processors and Physical Address Space
On processors that support Intel 64 architecture (CPUID.80000001:EDX[29] = 1), the size of the physical address
range is implementation-specific and indicated by CPUID.80000008H:EAX[bits 7-0].
For the format of information returned in EAX, see “CPUID—CPU Identification” in Chapter 3 of the Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 2A. See also: Chapter 4, “Paging.”
3.4
LOGICAL AND LINEAR ADDRESSES
At the system-architecture level in protected mode, the processor uses two stages of address translation to arrive
at a physical address: logical-address translation and linear address space paging.
Even with the minimum use of segments, every byte in the processor’s address space is accessed with a logical
address. A logical address consists of a 16-bit segment selector and a 32-bit offset (see Figure 3-5). The segment
selector identifies the segment the byte is located in and the offset specifies the location of the byte in the segment
relative to the base address of the segment.
The processor translates every logical address into a linear address. A linear address is a 32-bit address in the
processor’s linear address space. Like the physical address space, the linear address space is a flat (unsegmented),
232-byte address space, with addresses ranging from 0 to FFFFFFFFH. The linear address space contains all the
segments and system tables defined for a system.
To translate a logical address into a linear address, the processor does the following:
1. Uses the offset in the segment selector to locate the segment descriptor for the segment in the GDT or LDT and
reads it into the processor. (This step is needed only when a new segment selector is loaded into a segment
register.)
2. Examines the segment descriptor to check the access rights and range of the segment to insure that the
segment is accessible and that the offset is within the limits of the segment.
3. Adds the base address of the segment from the segment descriptor to the offset to form a linear address.
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Logical
Address
0
31(63)
Offset (Effective Address)
15
0
Seg. Selector
Descriptor Table
Segment
Descriptor
Base Address
+
31(63)
0
Linear Address
Figure 3-5. Logical Address to Linear Address Translation
If paging is not used, the processor maps the linear address directly to a physical address (that is, the linear
address goes out on the processor’s address bus). If the linear address space is paged, a second level of address
translation is used to translate the linear address into a physical address.
See also: Chapter 4, “Paging.”
3.4.1
Logical Address Translation in IA-32e Mode
In IA-32e mode, an Intel 64 processor uses the steps described above to translate a logical address to a linear
address. In 64-bit mode, the offset and base address of the segment are 64-bits instead of 32 bits. The linear
address format is also 64 bits wide and is subject to the canonical form requirement.
Each code segment descriptor provides an L bit. This bit allows a code segment to execute 64-bit code or legacy
32-bit code by code segment.
3.4.2
Segment Selectors
A segment selector is a 16-bit identifier for a segment (see Figure 3-6). It does not point directly to the segment,
but instead points to the segment descriptor that defines the segment. A segment selector contains the following
items:
Index
(Bits 3 through 15) — Selects one of 8192 descriptors in the GDT or LDT. The processor multiplies
the index value by 8 (the number of bytes in a segment descriptor) and adds the result to the base
address of the GDT or LDT (from the GDTR or LDTR register, respectively).
TI (table indicator) flag
(Bit 2) — Specifies the descriptor table to use: clearing this flag selects the GDT; setting this flag
selects the current LDT.
15
3 2 1 0
Index
T RPL
I
Table Indicator
0 = GDT
1 = LDT
Requested Privilege Level (RPL)
Figure 3-6. Segment Selector
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PROTECTED-MODE MEMORY MANAGEMENT
Requested Privilege Level (RPL)
(Bits 0 and 1) — Specifies the privilege level of the selector. The privilege level can range from 0 to
3, with 0 being the most privileged level. See Section 5.5, “Privilege Levels”, for a description of the
relationship of the RPL to the CPL of the executing program (or task) and the descriptor privilege
level (DPL) of the descriptor the segment selector points to.
The first entry of the GDT is not used by the processor. A segment selector that points to this entry of the GDT (that
is, a segment selector with an index of 0 and the TI flag set to 0) is used as a “null segment selector.” The processor
does not generate an exception when a segment register (other than the CS or SS registers) is loaded with a null
selector. It does, however, generate an exception when a segment register holding a null selector is used to access
memory. A null selector can be used to initialize unused segment registers. Loading the CS or SS register with a null
segment selector causes a general-protection exception (#GP) to be generated.
Segment selectors are visible to application programs as part of a pointer variable, but the values of selectors are
usually assigned or modified by link editors or linking loaders, not application programs.
3.4.3
Segment Registers
To reduce address translation time and coding complexity, the processor provides registers for holding up to 6
segment selectors (see Figure 3-7). Each of these segment registers support a specific kind of memory reference
(code, stack, or data). For virtually any kind of program execution to take place, at least the code-segment (CS),
data-segment (DS), and stack-segment (SS) registers must be loaded with valid segment selectors. The processor
also provides three additional data-segment registers (ES, FS, and GS), which can be used to make additional data
segments available to the currently executing program (or task).
For a program to access a segment, the segment selector for the segment must have been loaded in one of the
segment registers. So, although a system can define thousands of segments, only 6 can be available for immediate
use. Other segments can be made available by loading their segment selectors into these registers during program
execution.
Visible Part
Segment Selector
Hidden Part
Base Address, Limit, Access Information
CS
SS
DS
ES
FS
GS
Figure 3-7. Segment Registers
Every segment register has a “visible” part and a “hidden” part. (The hidden part is sometimes referred to as a
“descriptor cache” or a “shadow register.”) When a segment selector is loaded into the visible part of a segment
register, the processor also loads the hidden part of the segment register with the base address, segment limit, and
access control information from the segment descriptor pointed to by the segment selector. The information cached
in the segment register (visible and hidden) allows the processor to translate addresses without taking extra bus
cycles to read the base address and limit from the segment descriptor. In systems in which multiple processors
have access to the same descriptor tables, it is the responsibility of software to reload the segment registers when
the descriptor tables are modified. If this is not done, an old segment descriptor cached in a segment register might
be used after its memory-resident version has been modified.
Two kinds of load instructions are provided for loading the segment registers:
1. Direct load instructions such as the MOV, POP, LDS, LES, LSS, LGS, and LFS instructions. These instructions
explicitly reference the segment registers.
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2. Implied load instructions such as the far pointer versions of the CALL, JMP, and RET instructions, the SYSENTER
and SYSEXIT instructions, and the IRET, INTn, INTO and INT3 instructions. These instructions change the
contents of the CS register (and sometimes other segment registers) as an incidental part of their operation.
The MOV instruction can also be used to store visible part of a segment register in a general-purpose register.
3.4.4
Segment Loading Instructions in IA-32e Mode
Because ES, DS, and SS segment registers are not used in 64-bit mode, their fields (base, limit, and attribute) in
segment descriptor registers are ignored. Some forms of segment load instructions are also invalid (for example,
LDS, POP ES). Address calculations that reference the ES, DS, or SS segments are treated as if the segment base
is zero.
The processor checks that all linear-address references are in canonical form instead of performing limit checks.
Mode switching does not change the contents of the segment registers or the associated descriptor registers.
These registers are also not changed during 64-bit mode execution, unless explicit segment loads are performed.
In order to set up compatibility mode for an application, segment-load instructions (MOV to Sreg, POP Sreg) work
normally in 64-bit mode. An entry is read from the system descriptor table (GDT or LDT) and is loaded in the
hidden portion of the segment descriptor register. The descriptor-register base, limit, and attribute fields are all
loaded. However, the contents of the data and stack segment selector and the descriptor registers are ignored.
When FS and GS segment overrides are used in 64-bit mode, their respective base addresses are used in the linear
address calculation: (FS or GS).base + index + displacement. FS.base and GS.base are then expanded to the full
linear-address size supported by the implementation. The resulting effective address calculation can wrap across
positive and negative addresses; the resulting linear address must be canonical.
In 64-bit mode, memory accesses using FS-segment and GS-segment overrides are not checked for a runtime limit
nor subjected to attribute-checking. Normal segment loads (MOV to Sreg and POP Sreg) into FS and GS load a
standard 32-bit base value in the hidden portion of the segment descriptor register. The base address bits above
the standard 32 bits are cleared to 0 to allow consistency for implementations that use less than 64 bits.
The hidden descriptor register fields for FS.base and GS.base are physically mapped to MSRs in order to load all
address bits supported by a 64-bit implementation. Software with CPL = 0 (privileged software) can load all
supported linear-address bits into FS.base or GS.base using WRMSR. Addresses written into the 64-bit FS.base
and GS.base registers must be in canonical form. A WRMSR instruction that attempts to write a non-canonical
address to those registers causes a #GP fault.
When in compatibility mode, FS and GS overrides operate as defined by 32-bit mode behavior regardless of the
value loaded into the upper 32 linear-address bits of the hidden descriptor register base field. Compatibility mode
ignores the upper 32 bits when calculating an effective address.
A new 64-bit mode instruction, SWAPGS, can be used to load GS base. SWAPGS exchanges the kernel data structure pointer from the IA32_KernelGSbase MSR with the GS base register. The kernel can then use the GS prefix on
normal memory references to access the kernel data structures. An attempt to write a non-canonical value (using
WRMSR) to the IA32_KernelGSBase MSR causes a #GP fault.
3.4.5
Segment Descriptors
A segment descriptor is a data structure in a GDT or LDT that provides the processor with the size and location of
a segment, as well as access control and status information. Segment descriptors are typically created by
compilers, linkers, loaders, or the operating system or executive, but not application programs. Figure 3-8 illustrates the general descriptor format for all types of segment descriptors.
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31
24 23 22 21 20 19
Base 31:24
D
A
G / L V
B
L
31
16 15 14 13 12 11
Seg.
Limit
19:16
P
D
P
L
S
0
8 7
Type
Base 23:16
16 15
Base Address 15:00
4
0
Segment Limit 15:00
0
L
— 64-bit code segment (IA-32e mode only)
AVL — Available for use by system software
BASE — Segment base address
D/B — Default operation size (0 = 16-bit segment; 1 = 32-bit segment)
DPL — Descriptor privilege level
G
— Granularity
LIMIT — Segment Limit
P
— Segment present
S
— Descriptor type (0 = system; 1 = code or data)
TYPE — Segment type
Figure 3-8. Segment Descriptor
The flags and fields in a segment descriptor are as follows:
Segment limit field
Specifies the size of the segment. The processor puts together the two segment limit fields to form
a 20-bit value. The processor interprets the segment limit in one of two ways, depending on the
setting of the G (granularity) flag:
•
If the granularity flag is clear, the segment size can range from 1 byte to 1 MByte, in byte increments.
•
If the granularity flag is set, the segment size can range from 4 KBytes to 4 GBytes, in 4-KByte
increments.
The processor uses the segment limit in two different ways, depending on whether the segment is
an expand-up or an expand-down segment. See Section 3.4.5.1, “Code- and Data-Segment
Descriptor Types”, for more information about segment types. For expand-up segments, the offset
in a logical address can range from 0 to the segment limit. Offsets greater than the segment limit
generate general-protection exceptions (#GP, for all segment other than SS) or stack-fault exceptions (#SS for the SS segment). For expand-down segments, the segment limit has the reverse
function; the offset can range from the segment limit plus 1 to FFFFFFFFH or FFFFH, depending on
the setting of the B flag. Offsets less than or equal to the segment limit generate general-protection
exceptions or stack-fault exceptions. Decreasing the value in the segment limit field for an expanddown segment allocates new memory at the bottom of the segment's address space, rather than at
the top. IA-32 architecture stacks always grow downwards, making this mechanism convenient for
expandable stacks.
Base address fields
Defines the location of byte 0 of the segment within the 4-GByte linear address space. The
processor puts together the three base address fields to form a single 32-bit value. Segment base
addresses should be aligned to 16-byte boundaries. Although 16-byte alignment is not required,
this alignment allows programs to maximize performance by aligning code and data on 16-byte
boundaries.
Type field
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Indicates the segment or gate type and specifies the kinds of access that can be made to the
segment and the direction of growth. The interpretation of this field depends on whether the
descriptor type flag specifies an application (code or data) descriptor or a system descriptor. The
encoding of the type field is different for code, data, and system descriptors (see Figure 5-1). See
Section 3.4.5.1, “Code- and Data-Segment Descriptor Types”, for a description of how this field is
used to specify code and data-segment types.
PROTECTED-MODE MEMORY MANAGEMENT
S (descriptor type) flag
Specifies whether the segment descriptor is for a system segment (S flag is clear) or a code or data
segment (S flag is set).
DPL (descriptor privilege level) field
Specifies the privilege level of the segment. The privilege level can range from 0 to 3, with 0 being
the most privileged level. The DPL is used to control access to the segment. See Section 5.5, “Privilege Levels”, for a description of the relationship of the DPL to the CPL of the executing code
segment and the RPL of a segment selector.
P (segment-present) flag
Indicates whether the segment is present in memory (set) or not present (clear). If this flag is clear,
the processor generates a segment-not-present exception (#NP) when a segment selector that
points to the segment descriptor is loaded into a segment register. Memory management software
can use this flag to control which segments are actually loaded into physical memory at a given
time. It offers a control in addition to paging for managing virtual memory.
Figure 3-9 shows the format of a segment descriptor when the segment-present flag is clear. When
this flag is clear, the operating system or executive is free to use the locations marked “Available” to
store its own data, such as information regarding the whereabouts of the missing segment.
D/B (default operation size/default stack pointer size and/or upper bound) flag
Performs different functions depending on whether the segment descriptor is an executable code
segment, an expand-down data segment, or a stack segment. (This flag should always be set to 1
for 32-bit code and data segments and to 0 for 16-bit code and data segments.)
•
Executable code segment. The flag is called the D flag and it indicates the default length for
effective addresses and operands referenced by instructions in the segment. If the flag is set,
32-bit addresses and 32-bit or 8-bit operands are assumed; if it is clear, 16-bit addresses and
16-bit or 8-bit operands are assumed.
The instruction prefix 66H can be used to select an operand size other than the default, and the
prefix 67H can be used select an address size other than the default.
•
Stack segment (data segment pointed to by the SS register). The flag is called the B (big)
flag and it specifies the size of the stack pointer used for implicit stack operations (such as
pushes, pops, and calls). If the flag is set, a 32-bit stack pointer is used, which is stored in the
32-bit ESP register; if the flag is clear, a 16-bit stack pointer is used, which is stored in the 16bit SP register. If the stack segment is set up to be an expand-down data segment (described in
the next paragraph), the B flag also specifies the upper bound of the stack segment.
•
Expand-down data segment. The flag is called the B flag and it specifies the upper bound of
the segment. If the flag is set, the upper bound is FFFFFFFFH (4 GBytes); if the flag is clear, the
upper bound is FFFFH (64 KBytes).
31
16 15 14 13 12 11
Available
0
D
P
L
31
S
0
8 7
Type
Available
4
0
Available
0
Figure 3-9. Segment Descriptor When Segment-Present Flag Is Clear
G (granularity) flag
Determines the scaling of the segment limit field. When the granularity flag is clear, the segment
limit is interpreted in byte units; when flag is set, the segment limit is interpreted in 4-KByte units.
(This flag does not affect the granularity of the base address; it is always byte granular.) When the
granularity flag is set, the twelve least significant bits of an offset are not tested when checking the
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offset against the segment limit. For example, when the granularity flag is set, a limit of 0 results in
valid offsets from 0 to 4095.
L (64-bit code segment) flag
In IA-32e mode, bit 21 of the second doubleword of the segment descriptor indicates whether a
code segment contains native 64-bit code. A value of 1 indicates instructions in this code segment
are executed in 64-bit mode. A value of 0 indicates the instructions in this code segment are
executed in compatibility mode. If L-bit is set, then D-bit must be cleared. When not in IA-32e mode
or for non-code segments, bit 21 is reserved and should always be set to 0.
Available and reserved bits
Bit 20 of the second doubleword of the segment descriptor is available for use by system software.
3.4.5.1
Code- and Data-Segment Descriptor Types
When the S (descriptor type) flag in a segment descriptor is set, the descriptor is for either a code or a data
segment. The highest order bit of the type field (bit 11 of the second double word of the segment descriptor) then
determines whether the descriptor is for a data segment (clear) or a code segment (set).
For data segments, the three low-order bits of the type field (bits 8, 9, and 10) are interpreted as accessed (A),
write-enable (W), and expansion-direction (E). See Table 3-1 for a description of the encoding of the bits in the
type field for code and data segments. Data segments can be read-only or read/write segments, depending on the
setting of the write-enable bit.
Table 3-1. Code- and Data-Segment Types
Type Field
Descriptor
Type
Description
Decimal
11
10
E
9
W
8
A
0
0
0
0
0
Data
Read-Only
1
0
0
0
1
Data
Read-Only, accessed
2
0
0
1
0
Data
Read/Write
3
0
0
1
1
Data
Read/Write, accessed
4
0
1
0
0
Data
Read-Only, expand-down
5
0
1
0
1
Data
Read-Only, expand-down, accessed
6
0
1
1
0
Data
Read/Write, expand-down
7
0
1
1
1
Data
Read/Write, expand-down, accessed
C
R
A
8
1
0
0
0
Code
Execute-Only
9
1
0
0
1
Code
Execute-Only, accessed
10
1
0
1
0
Code
Execute/Read
11
1
0
1
1
Code
Execute/Read, accessed
12
1
1
0
0
Code
Execute-Only, conforming
13
1
1
0
1
Code
Execute-Only, conforming, accessed
14
1
1
1
0
Code
Execute/Read, conforming
15
1
1
1
1
Code
Execute/Read, conforming, accessed
Stack segments are data segments which must be read/write segments. Loading the SS register with a segment
selector for a nonwritable data segment generates a general-protection exception (#GP). If the size of a stack
segment needs to be changed dynamically, the stack segment can be an expand-down data segment (expansiondirection flag set). Here, dynamically changing the segment limit causes stack space to be added to the bottom of
3-12 Vol. 3A
PROTECTED-MODE MEMORY MANAGEMENT
the stack. If the size of a stack segment is intended to remain static, the stack segment may be either an expandup or expand-down type.
The accessed bit indicates whether the segment has been accessed since the last time the operating-system or
executive cleared the bit. The processor sets this bit whenever it loads a segment selector for the segment into a
segment register, assuming that the type of memory that contains the segment descriptor supports processor
writes. The bit remains set until explicitly cleared. This bit can be used both for virtual memory management and
for debugging.
For code segments, the three low-order bits of the type field are interpreted as accessed (A), read enable (R), and
conforming (C). Code segments can be execute-only or execute/read, depending on the setting of the read-enable
bit. An execute/read segment might be used when constants or other static data have been placed with instruction
code in a ROM. Here, data can be read from the code segment either by using an instruction with a CS override
prefix or by loading a segment selector for the code segment in a data-segment register (the DS, ES, FS, or GS
registers). In protected mode, code segments are not writable.
Code segments can be either conforming or nonconforming. A transfer of execution into a more-privileged
conforming segment allows execution to continue at the current privilege level. A transfer into a nonconforming
segment at a different privilege level results in a general-protection exception (#GP), unless a call gate or task
gate is used (see Section 5.8.1, “Direct Calls or Jumps to Code Segments”, for more information on conforming and
nonconforming code segments). System utilities that do not access protected facilities and handlers for some types
of exceptions (such as, divide error or overflow) may be loaded in conforming code segments. Utilities that need to
be protected from less privileged programs and procedures should be placed in nonconforming code segments.
NOTE
Execution cannot be transferred by a call or a jump to a less-privileged (numerically higher
privilege level) code segment, regardless of whether the target segment is a conforming or
nonconforming code segment. Attempting such an execution transfer will result in a generalprotection exception.
All data segments are nonconforming, meaning that they cannot be accessed by less privileged programs or procedures (code executing at numerically high privilege levels). Unlike code segments, however, data segments can be
accessed by more privileged programs or procedures (code executing at numerically lower privilege levels) without
using a special access gate.
If the segment descriptors in the GDT or an LDT are placed in ROM, the processor can enter an indefinite loop if
software or the processor attempts to update (write to) the ROM-based segment descriptors. To prevent this
problem, set the accessed bits for all segment descriptors placed in a ROM. Also, remove operating-system or
executive code that attempts to modify segment descriptors located in ROM.
3.5
SYSTEM DESCRIPTOR TYPES
When the S (descriptor type) flag in a segment descriptor is clear, the descriptor type is a system descriptor. The
processor recognizes the following types of system descriptors:
•
•
•
•
•
•
Local descriptor-table (LDT) segment descriptor.
Task-state segment (TSS) descriptor.
Call-gate descriptor.
Interrupt-gate descriptor.
Trap-gate descriptor.
Task-gate descriptor.
These descriptor types fall into two categories: system-segment descriptors and gate descriptors. Systemsegment descriptors point to system segments (LDT and TSS segments). Gate descriptors are in themselves
“gates,” which hold pointers to procedure entry points in code segments (call, interrupt, and trap gates) or which
hold segment selectors for TSS’s (task gates).
Vol. 3A 3-13
PROTECTED-MODE MEMORY MANAGEMENT
Table 3-2 shows the encoding of the type field for system-segment descriptors and gate descriptors. Note that
system descriptors in IA-32e mode are 16 bytes instead of 8 bytes.
Table 3-2. System-Segment and Gate-Descriptor Types
Type Field
Description
Decimal
11
10
9
8
32-Bit Mode
IA-32e Mode
0
0
0
0
0
Reserved
Upper 8 byte of an 16-byte
descriptor
1
0
0
0
1
16-bit TSS (Available)
Reserved
2
0
0
1
0
LDT
LDT
3
0
0
1
1
16-bit TSS (Busy)
Reserved
4
0
1
0
0
16-bit Call Gate
Reserved
5
0
1
0
1
Task Gate
Reserved
6
0
1
1
0
16-bit Interrupt Gate
Reserved
7
0
1
1
1
16-bit Trap Gate
Reserved
8
1
0
0
0
Reserved
Reserved
9
1
0
0
1
32-bit TSS (Available)
64-bit TSS (Available)
10
1
0
1
0
Reserved
Reserved
11
1
0
1
1
32-bit TSS (Busy)
64-bit TSS (Busy)
12
1
1
0
0
32-bit Call Gate
64-bit Call Gate
13
1
1
0
1
Reserved
Reserved
14
1
1
1
0
32-bit Interrupt Gate
64-bit Interrupt Gate
15
1
1
1
1
32-bit Trap Gate
64-bit Trap Gate
See also: Section 3.5.1, “Segment Descriptor Tables”, and Section 7.2.2, “TSS Descriptor” (for more information
on the system-segment descriptors); see Section 5.8.3, “Call Gates”, Section 6.11, “IDT Descriptors”, and Section
7.2.5, “Task-Gate Descriptor” (for more information on the gate descriptors).
3.5.1
Segment Descriptor Tables
A segment descriptor table is an array of segment descriptors (see Figure 3-10). A descriptor table is variable in
length and can contain up to 8192 (213) 8-byte descriptors. There are two kinds of descriptor tables:
•
•
The global descriptor table (GDT)
The local descriptor tables (LDT)
3-14 Vol. 3A
PROTECTED-MODE MEMORY MANAGEMENT
T
I
Global
Descriptor
Table (GDT)
Local
Descriptor
Table (LDT)
TI = 0
TI = 1
Segment
Selector
First Descriptor in
GDT is Not Used
56
56
48
48
40
40
32
32
24
24
16
16
8
8
0
0
GDTR Register
LDTR Register
Limit
Base Address
Limit
Base Address
Seg. Sel.
Figure 3-10. Global and Local Descriptor Tables
Each system must have one GDT defined, which may be used for all programs and tasks in the system. Optionally,
one or more LDTs can be defined. For example, an LDT can be defined for each separate task being run, or some or
all tasks can share the same LDT.
The GDT is not a segment itself; instead, it is a data structure in linear address space. The base linear address and
limit of the GDT must be loaded into the GDTR register (see Section 2.4, “Memory-Management Registers”). The
base addresses of the GDT should be aligned on an eight-byte boundary to yield the best processor performance.
The limit value for the GDT is expressed in bytes. As with segments, the limit value is added to the base address to
get the address of the last valid byte. A limit value of 0 results in exactly one valid byte. Because segment descriptors are always 8 bytes long, the GDT limit should always be one less than an integral multiple of eight (that is, 8N
– 1).
The first descriptor in the GDT is not used by the processor. A segment selector to this “null descriptor” does not
generate an exception when loaded into a data-segment register (DS, ES, FS, or GS), but it always generates a
general-protection exception (#GP) when an attempt is made to access memory using the descriptor. By initializing
the segment registers with this segment selector, accidental reference to unused segment registers can be guaranteed to generate an exception.
The LDT is located in a system segment of the LDT type. The GDT must contain a segment descriptor for the LDT
segment. If the system supports multiple LDTs, each must have a separate segment selector and segment
descriptor in the GDT. The segment descriptor for an LDT can be located anywhere in the GDT. See Section 3.5,
“System Descriptor Types”, information on the LDT segment-descriptor type.
An LDT is accessed with its segment selector. To eliminate address translations when accessing the LDT, the
segment selector, base linear address, limit, and access rights of the LDT are stored in the LDTR register (see
Section 2.4, “Memory-Management Registers”).
When the GDTR register is stored (using the SGDT instruction), a 48-bit “pseudo-descriptor” is stored in memory
(see top diagram in Figure 3-11). To avoid alignment check faults in user mode (privilege level 3), the pseudoVol. 3A 3-15
PROTECTED-MODE MEMORY MANAGEMENT
descriptor should be located at an odd word address (that is, address MOD 4 is equal to 2). This causes the
processor to store an aligned word, followed by an aligned doubleword. User-mode programs normally do not store
pseudo-descriptors, but the possibility of generating an alignment check fault can be avoided by aligning pseudodescriptors in this way. The same alignment should be used when storing the IDTR register using the SIDT instruction. When storing the LDTR or task register (using the SLDT or STR instruction, respectively), the pseudodescriptor should be located at a doubleword address (that is, address MOD 4 is equal to 0).
47
16 15
79
0
Limit
32-bit Base Address
16 15
64-bit Base Address
0
Limit
Figure 3-11. Pseudo-Descriptor Formats
3.5.2
Segment Descriptor Tables in IA-32e Mode
In IA-32e mode, a segment descriptor table can contain up to 8192 (213) 8-byte descriptors. An entry in the
segment descriptor table can be 8 bytes. System descriptors are expanded to 16 bytes (occupying the space of two
entries).
GDTR and LDTR registers are expanded to hold 64-bit base address. The corresponding pseudo-descriptor is 80
bits. (see the bottom diagram in Figure 3-11).
The following system descriptors expand to 16 bytes:
— Call gate descriptors (see Section 5.8.3.1, “IA-32e Mode Call Gates”)
— IDT gate descriptors (see Section 6.14.1, “64-Bit Mode IDT”)
— LDT and TSS descriptors (see Section 7.2.3, “TSS Descriptor in 64-bit mode”).
3-16 Vol. 3A
CHAPTER 4
PAGING
Chapter 3 explains how segmentation converts logical addresses to linear addresses. Paging (or linear-address
translation) is the process of translating linear addresses so that they can be used to access memory or I/O
devices. Paging translates each linear address to a physical address and determines, for each translation, what
accesses to the linear address are allowed (the address’s access rights) and the type of caching used for such
accesses (the address’s memory type).
Intel-64 processors support three different paging modes. These modes are identified and defined in Section 4.1.
Section 4.2 gives an overview of the translation mechanism that is used in all modes. Section 4.3, Section 4.4, and
Section 4.5 discuss the three paging modes in detail.
Section 4.6 details how paging determines and uses access rights. Section 4.7 discusses exceptions that may be
generated by paging (page-fault exceptions). Section 4.8 considers data which the processor writes in response to
linear-address accesses (accessed and dirty flags).
Section 4.9 describes how paging determines the memory types used for accesses to linear addresses. Section 4.10
provides details of how a processor may cache information about linear-address translation. Section 4.11 outlines
interactions between paging and certain VMX features. Section 4.12 gives an overview of how paging can be used
to implement virtual memory.
4.1
PAGING MODES AND CONTROL BITS
Paging behavior is controlled by the following control bits:
•
•
The WP and PG flags in control register CR0 (bit 16 and bit 31, respectively).
•
The LME and NXE flags in the IA32_EFER MSR (bit 8 and bit 11, respectively).
The PSE, PAE, PGE, PCIDE, and SMEP flags in control register CR4 (bit 4, bit 5, bit 7, bit 17, and bit 20 respectively).
Software enables paging by using the MOV to CR0 instruction to set CR0.PG. Before doing so, software should
ensure that control register CR3 contains the physical address of the first paging structure that the processor will
use for linear-address translation (see Section 4.2) and that structure is initialized as desired. See Table 4-3,
Table 4-7, and Table 4-12 for the use of CR3 in the different paging modes.
Section 4.1.1 describes how the values of CR0.PG, CR4.PAE, and IA32_EFER.LME determine whether paging is in
use and, if so, which of three paging modes is in use. Section 4.1.2 explains how to manage these bits to establish
or make changes in paging modes. Section 4.1.3 discusses how CR0.WP, CR4.PSE, CR4.PGE, CR4.PCIDE,
CR4.SMEP, and IA32_EFER.NXE modify the operation of the different paging modes.
4.1.1
Three Paging Modes
If CR0.PG = 0, paging is not used. The logical processor treats all linear addresses as if they were physical
addresses. CR4.PAE and IA32_EFER.LME are ignored by the processor, as are CR0.WP, CR4.PSE, CR4.PGE,
CR4.SMEP, and IA32_EFER.NXE.
Paging is enabled if CR0.PG = 1. Paging can be enabled only if protection is enabled (CR0.PE = 1). If paging is
enabled, one of three paging modes is used. The values of CR4.PAE and IA32_EFER.LME determine which paging
mode is used:
•
If CR0.PG = 1 and CR4.PAE = 0, 32-bit paging is used. 32-bit paging is detailed in Section 4.3. 32-bit paging
uses CR0.WP, CR4.PSE, CR4.PGE, and CR4.SMEP as described in Section 4.1.3.
•
If CR0.PG = 1, CR4.PAE = 1, and IA32_EFER.LME = 0, PAE paging is used. PAE paging is detailed in Section
4.4. PAE paging uses CR0.WP, CR4.PGE, CR4.SMEP, and IA32_EFER.NXE as described in Section 4.1.3.
Vol. 3A 4-1
PAGING
•
If CR0.PG = 1, CR4.PAE = 1, and IA32_EFER.LME = 1, IA-32e paging is used.1 IA-32e paging is detailed in
Section 4.5. IA-32e paging uses CR0.WP, CR4.PGE, CR4.PCIDE, CR4.SMEP, and IA32_EFER.NXE as described
in Section 4.1.3. IA-32e paging is available only on processors that support the Intel 64 architecture.
The three paging modes differ with regard to the following details:
•
•
•
Linear-address width. The size of the linear addresses that can be translated.
•
Support for execute-disable access rights. In some paging modes, software can be prevented from fetching
instructions from pages that are otherwise readable.
•
Support for PCIDs. In some paging modes, software can enable a facility by which a logical processor caches
information for multiple linear-address spaces. The processor may retain cached information when software
switches between different linear-address spaces.
Physical-address width. The size of the physical addresses produced by paging.
Page size. The granularity at which linear addresses are translated. Linear addresses on the same page are
translated to corresponding physical addresses on the same page.
Table 4-1 illustrates the key differences between the three paging modes.
Table 4-1. Properties of Different Paging Modes
Paging
Mode
PG in
CR0
PAE in
CR4
LME in
IA32_EFER
Lin.Addr.
Width
Phys.Addr.
Width1
Page
Sizes
Supports
ExecuteDisable?
Supports
PCIDs?
None
0
N/A
N/A
32
32
N/A
No
No
32-bit
1
0
02
32
Up to
403
4 KB
4 MB4
No
No
PAE
1
1
0
32
Up to
52
4 KB
2 MB
Yes5
No
IA-32e
1
1
1
48
Up to
52
4 KB
2 MB
1 GB6
Yes5
Yes7
NOTES:
1. The physical-address width is always bounded by MAXPHYADDR; see Section 4.1.4.
2. The processor ensures that IA32_EFER.LME must be 0 if CR0.PG = 1 and CR4.PAE = 0.
3. 32-bit paging supports physical-address widths of more than 32 bits only for 4-MByte pages and only if the PSE-36 mechanism is
supported; see Section 4.1.4 and Section 4.3.
4. 4-MByte pages are used with 32-bit paging only if CR4.PSE = 1; see Section 4.3.
5. Execute-disable access rights are applied only if IA32_EFER.NXE = 1; see Section 4.6.
6. Not all processors that support IA-32e paging support 1-GByte pages; see Section 4.1.4.
7. PCIDs are used only if CR4.PCIDE = 1; see Section 4.10.1.
Because they are used only if IA32_EFER.LME = 0, 32-bit paging and PAE paging is used only in legacy protected
mode. Because legacy protected mode cannot produce linear addresses larger than 32 bits, 32-bit paging and PAE
paging translate 32-bit linear addresses.
Because it is used only if IA32_EFER.LME = 1, IA-32e paging is used only in IA-32e mode. (In fact, it is the use of
IA-32e paging that defines IA-32e mode.) IA-32e mode has two sub-modes:
•
Compatibility mode. This mode uses only 32-bit linear addresses. IA-32e paging treats bits 47:32 of such an
address as all 0.
1. The LMA flag in the IA32_EFER MSR (bit 10) is a status bit that indicates whether the logical processor is in IA-32e mode (and thus
using IA-32e paging). The processor always sets IA32_EFER.LMA to CR0.PG & IA32_EFER.LME. Software cannot directly modify
IA32_EFER.LMA; an execution of WRMSR to the IA32_EFER MSR ignores bit 10 of its source operand.
4-2 Vol. 3A
PAGING
•
64-bit mode. While this mode produces 64-bit linear addresses, the processor ensures that bits 63:47 of such
an address are identical.1 IA-32e paging does not use bits 63:48 of such addresses.
4.1.2
Paging-Mode Enabling
If CR0.PG = 1, a logical processor is in one of three paging modes, depending on the values of CR4.PAE and
IA32_EFER.LME. Figure 4-1 illustrates how software can enable these modes and make transitions between them.
The following items identify certain limitations and other details:
#GP
#GP
Set LME
No Paging
Set PG
PG = 0
PAE = 0
LME = 0
Clear PG
Set LME
32-bit Paging
PG = 1
PAE = 0
LME = 0
PAE Paging
PG = 1
PAE = 1
LME = 0
Clear PAE
Clear LME
Setr LME
#GP
Clear PAE
Set PG
Set PAE
Clear PG
No Paging
PG = 0
PAE = 0
LME = 1
Clear PAE
No Paging
PG = 0
PAE = 1
LME = 0
Clear PG
Clear LME
Clear PAE
IA-32e Paging
PG = 1
PAE = 1
LME = 1
Set PG
Clear LME
Setr LME
Set PG
#GP
Set PAE
Set PAE
#GP
No Paging
PG = 0
PAE = 1
LME = 1
Figure 4-1. Enabling and Changing Paging Modes
•
IA32_EFER.LME cannot be modified while paging is enabled (CR0.PG = 1). Attempts to do so using WRMSR
cause a general-protection exception (#GP(0)).
•
Paging cannot be enabled (by setting CR0.PG to 1) while CR4.PAE = 0 and IA32_EFER.LME = 1. Attempts to do
so using MOV to CR0 cause a general-protection exception (#GP(0)).
•
CR4.PAE cannot be cleared while IA-32e paging is active (CR0.PG = 1 and IA32_EFER.LME = 1). Attempts to
do so using MOV to CR4 cause a general-protection exception (#GP(0)).
•
Regardless of the current paging mode, software can disable paging by clearing CR0.PG with MOV to CR0.2
1. Such an address is called canonical. Use of a non-canonical linear address in 64-bit mode produces a general-protection exception
(#GP(0)); the processor does not attempt to translate non-canonical linear addresses using IA-32e paging.
2. If CR4.PCIDE = 1, an attempt to clear CR0.PG causes a general-protection exception (#GP); software should clear CR4.PCIDE before
attempting to disable paging.
Vol. 3A 4-3
PAGING
•
Software can make transitions between 32-bit paging and PAE paging by changing the value of CR4.PAE with
MOV to CR4.
•
Software cannot make transitions directly between IA-32e paging and either of the other two paging modes. It
must first disable paging (by clearing CR0.PG with MOV to CR0), then set CR4.PAE and IA32_EFER.LME to the
desired values (with MOV to CR4 and WRMSR), and then re-enable paging (by setting CR0.PG with MOV to
CR0). As noted earlier, an attempt to clear either CR4.PAE or IA32_EFER.LME cause a general-protection
exception (#GP(0)).
•
VMX transitions allow transitions between paging modes that are not possible using MOV to CR or WRMSR. This
is because VMX transitions can load CR0, CR4, and IA32_EFER in one operation. See Section 4.11.1.
4.1.3
Paging-Mode Modifiers
Details of how each paging mode operates are determined by the following control bits:
•
•
•
The WP flag in CR0 (bit 16).
The PSE, PGE, PCIDE, and SMEP flags in CR4 (bit 4, bit 7, bit 17, and bit 20, respectively).
The NXE flag in the IA32_EFER MSR (bit 11).
CR0.WP allows pages to be protected from supervisor-mode writes. If CR0.WP = 0, supervisor-mode write
accesses are allowed to linear addresses with read-only access rights; if CR0.WP = 1, they are not. (User-mode
write accesses are never allowed to linear addresses with read-only access rights, regardless of the value of
CR0.WP.) Section 4.6 explains how access rights are determined, including the definition of supervisor-mode and
user-mode accesses.
CR4.PSE enables 4-MByte pages for 32-bit paging. If CR4.PSE = 0, 32-bit paging can use only 4-KByte pages; if
CR4.PSE = 1, 32-bit paging can use both 4-KByte pages and 4-MByte pages. See Section 4.3 for more information.
(PAE paging and IA-32e paging can use multiple page sizes regardless of the value of CR4.PSE.)
CR4.PGE enables global pages. If CR4.PGE = 0, no translations are shared across address spaces; if CR4.PGE = 1,
specified translations may be shared across address spaces. See Section 4.10.2.4 for more information.
CR4.PCIDE enables process-context identifiers (PCIDs) for IA-32e paging (CR4.PCIDE can be 1 only when IA-32e
paging is in use). PCIDs allow a logical processor to cache information for multiple linear-address spaces. See
Section 4.10.1 for more information.
CR4.SMEP allows pages to be protected from supervisor-mode instruction fetches. If CR4.SMEP = 1, software
operating in supervisor mode cannot fetch instructions from linear addresses that are accessible in user mode.
Section 4.6 explains how access rights are determined, including the definition of supervisor-mode accesses and
user-mode accessibility.
IA32_EFER.NXE enables execute-disable access rights for PAE paging and IA-32e paging. If IA32_EFER.NXE = 1,
instructions fetches can be prevented from specified linear addresses (even if data reads from the addresses are
allowed). Section 4.6 explains how access rights are determined. (IA32_EFER.NXE has no effect with 32-bit
paging. Software that wants to use this feature to limit instruction fetches from readable pages must use either PAE
paging or IA-32e paging.)
4.1.4
Enumeration of Paging Features by CPUID
Software can discover support for different paging features using the CPUID instruction:
•
PSE: page-size extensions for 32-bit paging.
If CPUID.01H:EDX.PSE [bit 3] = 1, CR4.PSE may be set to 1, enabling support for 4-MByte pages with 32-bit
paging (see Section 4.3).
•
PAE: physical-address extension.
If CPUID.01H:EDX.PAE [bit 6] = 1, CR4.PAE may be set to 1, enabling PAE paging (this setting is also required
for IA-32e paging).
•
PGE: global-page support.
If CPUID.01H:EDX.PGE [bit 13] = 1, CR4.PGE may be set to 1, enabling the global-page feature (see Section
4.10.2.4).
4-4 Vol. 3A
PAGING
•
PAT: page-attribute table.
If CPUID.01H:EDX.PAT [bit 16] = 1, the 8-entry page-attribute table (PAT) is supported. When the PAT is
supported, three bits in certain paging-structure entries select a memory type (used to determine type of
caching used) from the PAT (see Section 4.9.2).
•
PSE-36: page-size extensions with 40-bit physical-address extension.
If CPUID.01H:EDX.PSE-36 [bit 17] = 1, the PSE-36 mechanism is supported, indicating that translations using
4-MByte pages with 32-bit paging may produce physical addresses with up to 40 bits (see Section 4.3).
•
PCID: process-context identifiers.
If CPUID.01H:ECX.PCID [bit 17] = 1, CR4.PCIDE may be set to 1, enabling process-context identifiers (see
Section 4.10.1).
•
SMEP: supervisor-mode execution prevention.
If CPUID.(EAX=07H,ECX=0H):EBX.SMEP [bit 7] = 1, CR4.SMEP may be set to 1, enabling supervisor-mode
execution prevention (see Section 4.6).
•
NX: execute disable.
If CPUID.80000001H:EDX.NX [bit 20] = 1, IA32_EFER.NXE may be set to 1, allowing PAE paging and IA-32e
paging to disable execute access to selected pages (see Section 4.6). (Processors that do not support CPUID
function 80000001H do not allow IA32_EFER.NXE to be set to 1.)
•
Page1GB: 1-GByte pages.
If CPUID.80000001H:EDX.Page1GB [bit 26] = 1, 1-GByte pages are supported with IA-32e paging (see
Section 4.5).
•
LM: IA-32e mode support.
If CPUID.80000001H:EDX.LM [bit 29] = 1, IA32_EFER.LME may be set to 1, enabling IA-32e paging.
(Processors that do not support CPUID function 80000001H do not allow IA32_EFER.LME to be set to 1.)
•
CPUID.80000008H:EAX[7:0] reports the physical-address width supported by the processor. (For processors
that do not support CPUID function 80000008H, the width is generally 36 if CPUID.01H:EDX.PAE [bit 6] = 1
and 32 otherwise.) This width is referred to as MAXPHYADDR. MAXPHYADDR is at most 52.
•
CPUID.80000008H:EAX[15:8] reports the linear-address width supported by the processor. Generally, this
value is 48 if CPUID.80000001H:EDX.LM [bit 29] = 1 and 32 otherwise. (Processors that do not support CPUID
function 80000008H, support a linear-address width of 32.)
4.2
HIERARCHICAL PAGING STRUCTURES: AN OVERVIEW
All three paging modes translate linear addresses use hierarchical paging structures. This section provides an
overview of their operation. Section 4.3, Section 4.4, and Section 4.5 provide details for the three paging modes.
Every paging structure is 4096 Bytes in size and comprises a number of individual entries. With 32-bit paging,
each entry is 32 bits (4 bytes); there are thus 1024 entries in each structure. With PAE paging and IA-32e paging,
each entry is 64 bits (8 bytes); there are thus 512 entries in each structure. (PAE paging includes one exception, a
paging structure that is 32 bytes in size, containing 4 64-bit entries.)
The processor uses the upper portion of a linear address to identify a series of paging-structure entries. The last of
these entries identifies the physical address of the region to which the linear address translates (called the page
frame). The lower portion of the linear address (called the page offset) identifies the specific address within that
region to which the linear address translates.
Each paging-structure entry contains a physical address, which is either the address of another paging structure or
the address of a page frame. In the first case, the entry is said to reference the other paging structure; in the
latter, the entry is said to map a page.
The first paging structure used for any translation is located at the physical address in CR3. A linear address is
translated using the following iterative procedure. A portion of the linear address (initially the uppermost bits)
select an entry in a paging structure (initially the one located using CR3). If that entry references another paging
structure, the process continues with that paging structure and with the portion of the linear address immediately
below that just used. If instead the entry maps a page, the process completes: the physical address in the entry is
that of the page frame and the remaining lower portion of the linear address is the page offset.
Vol. 3A 4-5
PAGING
The following items give an example for each of the three paging modes (each example locates a 4-KByte page
frame):
•
With 32-bit paging, each paging structure comprises 1024 = 210 entries. For this reason, the translation
process uses 10 bits at a time from a 32-bit linear address. Bits 31:22 identify the first paging-structure entry
and bits 21:12 identify a second. The latter identifies the page frame. Bits 11:0 of the linear address are the
page offset within the 4-KByte page frame. (See Figure 4-2 for an illustration.)
•
With PAE paging, the first paging structure comprises only 4 = 22 entries. Translation thus begins by using
bits 31:30 from a 32-bit linear address to identify the first paging-structure entry. Other paging structures
comprise 512 =29 entries, so the process continues by using 9 bits at a time. Bits 29:21 identify a second
paging-structure entry and bits 20:12 identify a third. This last identifies the page frame. (See Figure 4-5 for
an illustration.)
•
With IA-32e paging, each paging structure comprises 512 = 29 entries and translation uses 9 bits at a time
from a 48-bit linear address. Bits 47:39 identify the first paging-structure entry, bits 38:30 identify a second,
bits 29:21 a third, and bits 20:12 identify a fourth. Again, the last identifies the page frame. (See Figure 4-8
for an illustration.)
The translation process in each of the examples above completes by identifying a page frame. However, the paging
structures may be configured so that translation terminates before doing so. This occurs if process encounters a
paging-structure entry that is marked “not present” (because its P flag — bit 0 — is clear) or in which a reserved bit
is set. In this case, there is no translation for the linear address; an access to that address causes a page-fault
exception (see Section 4.7).
In the examples above, a paging-structure entry maps a page with 4-KByte page frame when only 12 bits remain
in the linear address; entries identified earlier always reference other paging structures. That may not apply in
other cases. The following items identify when an entry maps a page and when it references another paging structure:
•
If more than 12 bits remain in the linear address, bit 7 (PS — page size) of the current paging-structure entry
is consulted. If the bit is 0, the entry references another paging structure; if the bit is 1, the entry maps a page.
•
If only 12 bits remain in the linear address, the current paging-structure entry always maps a page (bit 7 is
used for other purposes).
If a paging-structure entry maps a page when more than 12 bits remain in the linear address, the entry identifies
a page frame larger than 4 KBytes. For example, 32-bit paging uses the upper 10 bits of a linear address to locate
the first paging-structure entry; 22 bits remain. If that entry maps a page, the page frame is 222 Bytes = 4 MBytes.
32-bit paging supports 4-MByte pages if CR4.PSE = 1. PAE paging and IA-32e paging support 2-MByte pages
(regardless of the value of CR4.PSE). IA-32e paging may support 1-GByte pages (see Section 4.1.4).
Paging structures are given different names based their uses in the translation process. Table 4-2 gives the names
of the different paging structures. It also provides, for each structure, the source of the physical address used to
locate it (CR3 or a different paging-structure entry); the bits in the linear address used to select an entry from the
structure; and details of about whether and how such an entry can map a page.
4-6 Vol. 3A
PAGING
Table 4-2. Paging Structures in the Different Paging Modes
Paging Structure
Entry
Name
PML4 table
PML4E
Paging Mode
Physical
Address of
Structure
Bits Selecting
Entry
32-bit, PAE
IA-32e
N/A
CR3
47:39
32-bit
Page-directorypointer table
PDPTE
Page directory
PDE
Page table
PTE
Page Mapping
N/A (PS must be 0)
N/A
PAE
CR3
31:30
N/A (PS must be 0)
IA-32e
PML4E
38:30
1-GByte page if PS=11
32-bit
CR3
31:22
4-MByte page if PS=12
PAE, IA-32e
PDPTE
29:21
2-MByte page if PS=1
21:12
4-KByte page
20:12
4-KByte page
32-bit
PAE, IA-32e
PDE
NOTES:
1. Not all processors allow the PS flag to be 1 in PDPTEs; see Section 4.1.4 for how to determine whether 1-GByte pages are supported.
2. 32-bit paging ignores the PS flag in a PDE (and uses the entry to reference a page table) unless CR4.PSE = 1. Not all processors allow
CR4.PSE to be 1; see Section 4.1.4 for how to determine whether 4-MByte pages are supported with 32-bit paging.
4.3
32-BIT PAGING
A logical processor uses 32-bit paging if CR0.PG = 1 and CR4.PAE = 0. 32-bit paging translates 32-bit linear
addresses to 40-bit physical addresses.1 Although 40 bits corresponds to 1 TByte, linear addresses are limited to
32 bits; at most 4 GBytes of linear-address space may be accessed at any given time.
32-bit paging uses a hierarchy of paging structures to produce a translation for a linear address. CR3 is used to
locate the first paging-structure, the page directory. Table 4-3 illustrates how CR3 is used with 32-bit paging.
32-bit paging may map linear addresses to either 4-KByte pages or 4-MByte pages. Figure 4-2 illustrates the
translation process when it uses a 4-KByte page; Figure 4-3 covers the case of a 4-MByte page. The following
items describe the 32-bit paging process in more detail as well has how the page size is determined:
•
A 4-KByte naturally aligned page directory is located at the physical address specified in bits 31:12 of CR3 (see
Table 4-3). A page directory comprises 1024 32-bit entries (PDEs). A PDE is selected using the physical address
defined as follows:
— Bits 39:32 are all 0.
— Bits 31:12 are from CR3.
— Bits 11:2 are bits 31:22 of the linear address.
— Bits 1:0 are 0.
Because a PDE is identified using bits 31:22 of the linear address, it controls access to a 4-Mbyte region of the
linear-address space. Use of the PDE depends on CR.PSE and the PDE’s PS flag (bit 7):
1. Bits in the range 39:32 are 0 in any physical address used by 32-bit paging except those used to map 4-MByte pages. If the processor does not support the PSE-36 mechanism, this is true also for physical addresses used to map 4-MByte pages. If the processor
does support the PSE-36 mechanism and MAXPHYADDR < 40, bits in the range 39:MAXPHYADDR are 0 in any physical address used
to map a 4-MByte page. (The corresponding bits are reserved in PDEs.) See Section 4.1.4 for how to determine MAXPHYADDR and
whether the PSE-36 mechanism is supported.
Vol. 3A 4-7
PAGING
•
If CR4.PSE = 1 and the PDE’s PS flag is 1, the PDE maps a 4-MByte page (see Table 4-4). The final physical
address is computed as follows:
— Bits 39:32 are bits 20:13 of the PDE.
— Bits 31:22 are bits 31:22 of the PDE.1
— Bits 21:0 are from the original linear address.
•
If CR4.PSE = 0 or the PDE’s PS flag is 0, a 4-KByte naturally aligned page table is located at the physical
address specified in bits 31:12 of the PDE (see Table 4-5). A page table comprises 1024 32-bit entries (PTEs).
A PTE is selected using the physical address defined as follows:
— Bits 39:32 are all 0.
— Bits 31:12 are from the PDE.
— Bits 11:2 are bits 21:12 of the linear address.
— Bits 1:0 are 0.
•
Because a PTE is identified using bits 31:12 of the linear address, every PTE maps a 4-KByte page (see
Table 4-6). The final physical address is computed as follows:
— Bits 39:32 are all 0.
— Bits 31:12 are from the PTE.
— Bits 11:0 are from the original linear address.
If a paging-structure entry’s P flag (bit 0) is 0 or if the entry sets any reserved bit, the entry is used neither to reference another paging-structure entry nor to map a page. A reference using a linear address whose translation would
use such a paging-structure entry causes a page-fault exception (see Section 4.7).
With 32-bit paging, there are reserved bits only if CR4.PSE = 1:
•
If the P flag and the PS flag (bit 7) of a PDE are both 1, the bits reserved depend on MAXPHYADDR whether the
PSE-36 mechanism is supported:2
— If the PSE-36 mechanism is not supported, bits 21:13 are reserved.
— If the PSE-36 mechanism is supported, bits 21:(M–19) are reserved, where M is the minimum of 40 and
MAXPHYADDR.
•
If the PAT is not supported:3
— If the P flag of a PTE is 1, bit 7 is reserved.
— If the P flag and the PS flag of a PDE are both 1, bit 12 is reserved.
(If CR4.PSE = 0, no bits are reserved with 32-bit paging.)
A reference using a linear address that is successfully translated to a physical address is performed only if allowed
by the access rights of the translation; see Section 4.6.
1. The upper bits in the final physical address do not all come from corresponding positions in the PDE; the physical-address bits in the
PDE are not all contiguous.
2. See Section 4.1.4 for how to determine MAXPHYADDR and whether the PSE-36 mechanism is supported.
3. See Section 4.1.4 for how to determine whether the PAT is supported.
4-8 Vol. 3A
PAGING
Linear Address
31
22 21
12 11
Table
Directory
0
Offset
12
Page Table
10
10
4-KByte Page
Physical Address
Page Directory
PTE
20
PDE with PS=0
20
32
CR3
Figure 4-2. Linear-Address Translation to a 4-KByte Page using 32-Bit Paging
31
Linear Address
22 21
Offset
Directory
22
10
Page Directory
0
4-MByte Page
Physical Address
PDE with PS=1
18
32
CR3
Figure 4-3. Linear-Address Translation to a 4-MByte Page using 32-Bit Paging
Vol. 3A 4-9
PAGING
Figure 4-4 gives a summary of the formats of CR3 and the paging-structure entries with 32-bit paging. For the
paging structure entries, it identifies separately the format of entries that map pages, those that reference other
paging structures, and those that do neither because they are “not present”; bit 0 (P) and bit 7 (PS) are highlighted
because they determine how such an entry is used.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Address of page directory1
Bits 31:22 of address
of 2MB page frame
Reserved
(must be 0)
8
7
6
5
Address of page table
Ignored
G
Ignored
3
2
0
CR3
1 D A
P PW U R
C
/ / 1
D T S W
PDE:
4MB
page
I
g
n
P PW U R
C
/ / 1
D T S W
PDE:
page
table
0
A
Ignored
Address of 4KB page frame
1
P PW
C
Ignored
D T
Ignored
P
Bits 39:32 of A
address2
T
4
0
Ignored
G
P
P
U R
A D A C PW
/ / 1
T
T
D
S W
Ignored
0
PDE:
not
present
PTE:
4KB
page
PTE:
not
present
Figure 4-4. Formats of CR3 and Paging-Structure Entries with 32-Bit Paging
NOTES:
1. CR3 has 64 bits on processors supporting the Intel-64 architecture. These bits are ignored with 32-bit paging.
2. This example illustrates a processor in which MAXPHYADDR is 36. If this value is larger or smaller, the number of bits reserved in
positions 20:13 of a PDE mapping a 4-MByte will change.
Table 4-3. Use of CR3 with 32-Bit Paging
Bit
Position(s)
Contents
2:0
Ignored
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the page directory during linearaddress translation (see Section 4.9)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the page directory during linearaddress translation (see Section 4.9)
11:5
Ignored
31:12
Physical address of the 4-KByte aligned page directory used for linear-address translation
63:32
Ignored (these bits exist only on processors supporting the Intel-64 architecture)
4-10 Vol. 3A
PAGING
Table 4-4. Format of a 32-Bit Page-Directory Entry that Maps a 4-MByte Page
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to map a 4-MByte page
1 (R/W)
Read/write; if 0, writes may not be allowed to the 4-MByte page referenced by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 4-MByte page referenced by this entry (see Section
4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the 4-MByte page referenced by
this entry (see Section 4.9)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the 4-MByte page referenced by
this entry (see Section 4.9)
5 (A)
Accessed; indicates whether software has accessed the 4-MByte page referenced by this entry (see Section 4.8)
6 (D)
Dirty; indicates whether software has written to the 4-MByte page referenced by this entry (see Section 4.8)
7 (PS)
Page size; must be 1 (otherwise, this entry references a page table; see Table 4-5)
8 (G)
Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise
11:9
Ignored
12 (PAT)
If the PAT is supported, indirectly determines the memory type used to access the 4-MByte page referenced by this
entry (see Section 4.9.2); otherwise, reserved (must be 0)1
(M–20):13
Bits (M–1):32 of physical address of the 4-MByte page referenced by this entry2
21:(M–19)
Reserved (must be 0)
31:22
Bits 31:22 of physical address of the 4-MByte page referenced by this entry
NOTES:
1. See Section 4.1.4 for how to determine whether the PAT is supported.
2. If the PSE-36 mechanism is not supported, M is 32, and this row does not apply. If the PSE-36 mechanism is supported, M is the minimum of 40 and MAXPHYADDR (this row does not apply if MAXPHYADDR = 32). See Section 4.1.4 for how to determine MAXPHYADDR and whether the PSE-36 mechanism is supported.
Vol. 3A 4-11
PAGING
Table 4-5. Format of a 32-Bit Page-Directory Entry that References a Page Table
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to reference a page table
1 (R/W)
Read/write; if 0, writes may not be allowed to the 4-MByte region controlled by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 4-MByte region controlled by this entry (see Section
4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9)
5 (A)
Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)
6
Ignored
7 (PS)
If CR4.PSE = 1, must be 0 (otherwise, this entry maps a 4-MByte page; see Table 4-4); otherwise, ignored
11:8
Ignored
31:12
Physical address of 4-KByte aligned page table referenced by this entry
Table 4-6. Format of a 32-Bit Page-Table Entry that Maps a 4-KByte Page
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to map a 4-KByte page
1 (R/W)
Read/write; if 0, writes may not be allowed to the 4-KByte page referenced by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 4-KByte page referenced by this entry (see Section
4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9)
5 (A)
Accessed; indicates whether software has accessed the 4-KByte page referenced by this entry (see Section 4.8)
6 (D)
Dirty; indicates whether software has written to the 4-KByte page referenced by this entry (see Section 4.8)
7 (PAT)
If the PAT is supported, indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9.2); otherwise, reserved (must be 0)1
8 (G)
Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise
11:9
Ignored
31:12
Physical address of the 4-KByte page referenced by this entry
NOTES:
1. See Section 4.1.4 for how to determine whether the PAT is supported.
4-12 Vol. 3A
PAGING
4.4
PAE PAGING
A logical processor uses PAE paging if CR0.PG = 1, CR4.PAE = 1, and IA32_EFER.LME = 0. PAE paging translates
32-bit linear addresses to 52-bit physical addresses.1 Although 52 bits corresponds to 4 PBytes, linear addresses
are limited to 32 bits; at most 4 GBytes of linear-address space may be accessed at any given time.
With PAE paging, a logical processor maintains a set of four (4) PDPTE registers, which are loaded from an address
in CR3. Linear address are translated using 4 hierarchies of in-memory paging structures, each located using one
of the PDPTE registers. (This is different from the other paging modes, in which there is one hierarchy referenced
by CR3.)
Section 4.4.1 discusses the PDPTE registers. Section 4.4.2 describes linear-address translation with PAE paging.
4.4.1
PDPTE Registers
When PAE paging is used, CR3 references the base of a 32-Byte page-directory-pointer table. Table 4-7 illustrates how CR3 is used with PAE paging.
Table 4-7. Use of CR3 with PAE Paging
Bit
Position(s)
Contents
4:0
Ignored
31:5
Physical address of the 32-Byte aligned page-directory-pointer table used for linear-address translation
63:32
Ignored (these bits exist only on processors supporting the Intel-64 architecture)
The page-directory-pointer-table comprises four (4) 64-bit entries called PDPTEs. Each PDPTE controls access to a
1-GByte region of the linear-address space. Corresponding to the PDPTEs, the logical processor maintains a set of
four (4) internal, non-architectural PDPTE registers, called PDPTE0, PDPTE1, PDPTE2, and PDPTE3. The logical
processor loads these registers from the PDPTEs in memory as part of certain operations:
•
If PAE paging would be in use following an execution of MOV to CR0 or MOV to CR4 (see Section 4.1.1) and the
instruction is modifying any of CR0.CD, CR0.NW, CR0.PG, CR4.PAE, CR4.PGE, CR4.PSE, or CR4.SMEP; then the
PDPTEs are loaded from the address in CR3.
•
If MOV to CR3 is executed while the logical processor is using PAE paging, the PDPTEs are loaded from the
address being loaded into CR3.
•
If PAE paging is in use and a task switch changes the value of CR3, the PDPTEs are loaded from the address in
the new CR3 value.
•
Certain VMX transitions load the PDPTE registers. See Section 4.11.1.
Table 4-8 gives the format of a PDPTE. If any of the PDPTEs sets both the P flag (bit 0) and any reserved bit, the
MOV to CR instruction causes a general-protection exception (#GP(0)) and the PDPTEs are not loaded.2 As shown
in Table 4-8, bits 2:1, 8:5, and 63:MAXPHYADDR are reserved in the PDPTEs.
1. If MAXPHYADDR < 52, bits in the range 51:MAXPHYADDR will be 0 in any physical address used by PAE paging. (The corresponding
bits are reserved in the paging-structure entries.) See Section 4.1.4 for how to determine MAXPHYADDR.
2. On some processors, reserved bits are checked even in PDPTEs in which the P flag (bit 0) is 0.
Vol. 3A 4-13
PAGING
Table 4-8. Format of a PAE Page-Directory-Pointer-Table Entry (PDPTE)
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to reference a page directory
2:1
Reserved (must be 0)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the page directory referenced by
this entry (see Section 4.9)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the page directory referenced by
this entry (see Section 4.9)
8:5
Reserved (must be 0)
11:9
Ignored
(M–1):12
Physical address of 4-KByte aligned page directory referenced by this entry1
63:M
Reserved (must be 0)
NOTES:
1. M is an abbreviation for MAXPHYADDR, which is at most 52; see Section 4.1.4.
4.4.2
Linear-Address Translation with PAE Paging
PAE paging may map linear addresses to either 4-KByte pages or 2-MByte pages. Figure 4-5 illustrates the translation process when it produces a 4-KByte page; Figure 4-6 covers the case of a 2-MByte page. The following items
describe the PAE paging process in more detail as well has how the page size is determined:
•
Bits 31:30 of the linear address select a PDPTE register (see Section 4.4.1); this is PDPTEi, where i is the value
of bits 31:30.1 Because a PDPTE register is identified using bits 31:30 of the linear address, it controls access
to a 1-GByte region of the linear-address space. If the P flag (bit 0) of PDPTEi is 0, the processor ignores bits
63:1, and there is no mapping for the 1-GByte region controlled by PDPTEi. A reference using a linear address
in this region causes a page-fault exception (see Section 4.7).
•
If the P flag of PDPTEi is 1, 4-KByte naturally aligned page directory is located at the physical address specified
in bits 51:12 of PDPTEi (see Table 4-8 in Section 4.4.1) A page directory comprises 512 64-bit entries (PDEs).
A PDE is selected using the physical address defined as follows:
— Bits 51:12 are from PDPTEi.
— Bits 11:3 are bits 29:21 of the linear address.
— Bits 2:0 are 0.
Because a PDE is identified using bits 31:21 of the linear address, it controls access to a 2-Mbyte region of the
linear-address space. Use of the PDE depends on its PS flag (bit 7):
•
If the PDE’s PS flag is 1, the PDE maps a 2-MByte page (see Table 4-9). The final physical address is computed
as follows:
— Bits 51:21 are from the PDE.
— Bits 20:0 are from the original linear address.
•
If the PDE’s PS flag is 0, a 4-KByte naturally aligned page table is located at the physical address specified in
bits 51:12 of the PDE (see Table 4-10). A page directory comprises 512 64-bit entries (PTEs). A PTE is selected
using the physical address defined as follows:
— Bits 51:12 are from the PDE.
1. With PAE paging, the processor does not use CR3 when translating a linear address (as it does the other paging modes). It does not
access the PDPTEs in the page-directory-pointer table during linear-address translation.
4-14 Vol. 3A
PAGING
— Bits 11:3 are bits 20:12 of the linear address.
— Bits 2:0 are 0.
•
Because a PTE is identified using bits 31:12 of the linear address, every PTE maps a 4-KByte page (see
Table 4-11). The final physical address is computed as follows:
— Bits 51:12 are from the PTE.
— Bits 11:0 are from the original linear address.
If the P flag (bit 0) of a PDE or a PTE is 0 or if a PDE or a PTE sets any reserved bit, the entry is used neither to
reference another paging-structure entry nor to map a page. A reference using a linear address whose translation
would use such a paging-structure entry causes a page-fault exception (see Section 4.7).
The following bits are reserved with PAE paging:
•
•
•
•
If the P flag (bit 0) of a PDE or a PTE is 1, bits 62:MAXPHYADDR are reserved.
If the P flag and the PS flag (bit 7) of a PDE are both 1, bits 20:13 are reserved.
If IA32_EFER.NXE = 0 and the P flag of a PDE or a PTE is 1, the XD flag (bit 63) is reserved.
If the PAT is not supported:1
— If the P flag of a PTE is 1, bit 7 is reserved.
— If the P flag and the PS flag of a PDE are both 1, bit 12 is reserved.
A reference using a linear address that is successfully translated to a physical address is performed only if allowed
by the access rights of the translation; see Section 4.6.
Directory Pointer
Linear Address
31 30 29
21 20
12 11
Table
Directory
0
Offset
12
Page Table
Page Directory
PTE
2
Physical Address
9
9
PDE with PS=0
4-KByte Page
40
40
PDPTE Registers
40
PDPTE value
Figure 4-5. Linear-Address Translation to a 4-KByte Page using PAE Paging
1. See Section 4.1.4 for how to determine whether the PAT is supported.
Vol. 3A 4-15
PAGING
Directory
Pointer
Linear Address
31 30 29
21 20
Offset
Directory
0
21
9
Page Directory
2-MByte Page
Physical Address
PDPTE Registers
2
PDE with PS=1
PDPTE value
31
40
Figure 4-6. Linear-Address Translation to a 2-MByte Page using PAE Paging
Table 4-9. Format of a PAE Page-Directory Entry that Maps a 2-MByte Page
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to map a 2-MByte page
1 (R/W)
Read/write; if 0, writes may not be allowed to the 2-MByte page referenced by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 2-MByte page referenced by this entry (see Section
4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the 2-MByte page referenced by
this entry (see Section 4.9)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the 2-MByte page referenced by this
entry (see Section 4.9)
5 (A)
Accessed; indicates whether software has accessed the 2-MByte page referenced by this entry (see Section 4.8)
6 (D)
Dirty; indicates whether software has written to the 2-MByte page referenced by this entry (see Section 4.8)
7 (PS)
Page size; must be 1 (otherwise, this entry references a page table; see Table 4-10)
8 (G)
Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise
11:9
Ignored
12 (PAT)
If the PAT is supported, indirectly determines the memory type used to access the 2-MByte page referenced by this
entry (see Section 4.9.2); otherwise, reserved (must be 0)1
20:13
Reserved (must be 0)
(M–1):21
Physical address of the 2-MByte page referenced by this entry
62:M
Reserved (must be 0)
63 (XD)
If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 2-MByte page controlled by
this entry; see Section 4.6); otherwise, reserved (must be 0)
NOTES:
1. See Section 4.1.4 for how to determine whether the PAT is supported.
4-16 Vol. 3A
PAGING
Table 4-10. Format of a PAE Page-Directory Entry that References a Page Table
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to reference a page table
1 (R/W)
Read/write; if 0, writes may not be allowed to the 2-MByte region controlled by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 2-MByte region controlled by this entry (see
Section 4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9)
5 (A)
Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)
6
Ignored
7 (PS)
Page size; must be 0 (otherwise, this entry maps a 2-MByte page; see Table 4-9)
11:8
Ignored
(M–1):12
Physical address of 4-KByte aligned page table referenced by this entry
62:M
Reserved (must be 0)
63 (XD)
If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 2-MByte region controlled
by this entry; see Section 4.6); otherwise, reserved (must be 0)
Table 4-11. Format of a PAE Page-Table Entry that Maps a 4-KByte Page
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to map a 4-KByte page
1 (R/W)
Read/write; if 0, writes may not be allowed to the 4-KByte page referenced by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 4-KByte page referenced by this entry (see Section
4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the 4-KByte page referenced by
this entry (see Section 4.9)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9)
5 (A)
Accessed; indicates whether software has accessed the 4-KByte page referenced by this entry (see Section 4.8)
6 (D)
Dirty; indicates whether software has written to the 4-KByte page referenced by this entry (see Section 4.8)
7 (PAT)
If the PAT is supported, indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9.2); otherwise, reserved (must be 0)1
8 (G)
Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise
Vol. 3A 4-17
PAGING
Table 4-11. Format of a PAE Page-Table Entry that Maps a 4-KByte Page (Contd.)
Bit
Position(s)
Contents
11:9
Ignored
(M–1):12
Physical address of the 4-KByte page referenced by this entry
62:M
Reserved (must be 0)
63 (XD)
If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 4-KByte page controlled by
this entry; see Section 4.6); otherwise, reserved (must be 0)
NOTES:
1. See Section 4.1.4 for how to determine whether the PAT is supported.
Figure 4-7 gives a summary of the formats of CR3 and the paging-structure entries with PAE paging. For the paging
structure entries, it identifies separately the format of entries that map pages, those that reference other paging
structures, and those that do neither because they are “not present”; bit 0 (P) and bit 7 (PS) are highlighted
because they determine how a paging-structure entry is used.
6666555555555
3210987654321
Ignored2
Reserved3
M1 M-1
33322222222221111111111
210987654321098765432109876543210
Address of page-directory-pointer table
Address of page directory
Ign.
Ignored
Rsvd.
P P Rs
PDPTE:
CW
1
present
D T vd
Ignored
X
D
4
X
D
Reserved
Reserved
Address of
2MB page frame
0
Reserved
Address of page table
Reserved
Address of 4KB page frame
PDE:
2MB
page
I PPUR
0 g A C W /S
/ 1
n DT W
PDE:
page
table
Ign.
0
P
PPUR
Ign. G A D A C W /S
/ 1
T
DT W
Ignored
Figure 4-7. Formats of CR3 and Paging-Structure Entries with PAE Paging
NOTES:
1. M is an abbreviation for MAXPHYADDR.
2. CR3 has 64 bits only on processors supporting the Intel-64 architecture. These bits are ignored with PAE paging.
3. Reserved fields must be 0.
4. If IA32_EFER.NXE = 0 and the P flag of a PDE or a PTE is 1, the XD flag (bit 63) is reserved.
4-18 Vol. 3A
PDTPE:
not
present
P
PPUR
A Ign. G 1 D A C W /S
/ 1
T
DT W
Ignored
X
D
CR3
0
PDE:
not
present
PTE:
4KB
page
PTE:
not
present
PAGING
4.5
IA-32E PAGING
A logical processor uses IA-32e paging if CR0.PG = 1, CR4.PAE = 1, and IA32_EFER.LME = 1. With IA-32e paging,
linear address are translated using a hierarchy of in-memory paging structures located using the contents of CR3.
IA-32e paging translates 48-bit linear addresses to 52-bit physical addresses.1 Although 52 bits corresponds to 4
PBytes, linear addresses are limited to 48 bits; at most 256 TBytes of linear-address space may be accessed at any
given time.
IA-32e paging uses a hierarchy of paging structures to produce a translation for a linear address. CR3 is used to
locate the first paging-structure, the PML4 table. Use of CR3 with IA-32e paging depends on whether processcontext identifiers (PCIDs) have been enabled by setting CR4.PCIDE:
•
Table 4-12 illustrates how CR3 is used with IA-32e paging if CR4.PCIDE = 0.
Table 4-12. Use of CR3 with IA-32e Paging and CR4.PCIDE = 0
Bit
Position(s)
Contents
2:0
Ignored
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the PML4 table during linearaddress translation (see Section 4.9.2)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the PML4 table during linear-address
translation (see Section 4.9.2)
11:5
Ignored
M–1:12
Physical address of the 4-KByte aligned PML4 table used for linear-address translation1
63:M
Reserved (must be 0)
NOTES:
1. M is an abbreviation for MAXPHYADDR, which is at most 52; see Section 4.1.4.
•
Table 4-13 illustrates how CR3 is used with IA-32e paging if CR4.PCIDE = 1.
Table 4-13. Use of CR3 with IA-32e Paging and CR4.PCIDE = 1
Bit
Position(s)
Contents
11:0
PCID (see Section 4.10.1)1
M–1:12
Physical address of the 4-KByte aligned PML4 table used for linear-address translation2
63:M
Reserved (must be 0)3
NOTES:
1. Section 4.9.2 explains how the processor determines the memory type used to access the PML4 table during linear-address translation with CR4.PCIDE = 1.
2. M is an abbreviation for MAXPHYADDR, which is at most 52; see Section 4.1.4.
3. See Section 4.10.4.1 for use of bit 63 of the source operand of the MOV to CR3 instruction.
After software modifies the value of CR4.PCIDE, the logical processor immediately begins using CR3 as specified
for the new value. For example, if software changes CR4.PCIDE from 1 to 0, the current PCID immediately changes
1. If MAXPHYADDR < 52, bits in the range 51:MAXPHYADDR will be 0 in any physical address used by IA-32e paging. (The corresponding bits are reserved in the paging-structure entries.) See Section 4.1.4 for how to determine MAXPHYADDR.
Vol. 3A 4-19
PAGING
from CR3[11:0] to 000H (see also Section 4.10.4.1). In addition, the logical processor subsequently determines
the memory type used to access the PML4 table using CR3.PWT and CR3.PCD, which had been bits 4:3 of the PCID.
IA-32e paging may map linear addresses to 4-KByte pages, 2-MByte pages, or 1-GByte pages.1 Figure 4-8 illustrates the translation process when it produces a 4-KByte page; Figure 4-9 covers the case of a 2-MByte page, and
Figure 4-10 the case of a 1-GByte page.
47
Linear Address
39 38
30 29
21 20
PML4
Directory
Table
Directory Ptr
9
9
9
12 11
0
Offset
12 4-KByte Page
Physical Addr
PTE
Page-DirectoryPointer Table
PDPTE
PDE with PS=0
40
Page-Directory
40
Page Table
40
9
40
PML4E
40
CR3
Figure 4-8. Linear-Address Translation to a 4-KByte Page using IA-32e Paging
1. Not all processors support 1-GByte pages; see Section 4.1.4.
4-20 Vol. 3A
PAGING
47
Linear Address
39 38
21 20
30 29
Directory
PML4
Directory Ptr
0
Offset
21
9
9
2-MByte Page
Physical Addr
Page-DirectoryPointer Table
PDE with PS=1
31
Page-Directory
PDPTE
40
9
40
PML4E
40
CR3
Figure 4-9. Linear-Address Translation to a 2-MByte Page using IA-32e Paging
47
Linear Address
39 38
30 29
PML4
Directory Ptr
0
Offset
30
9
1-GByte Page
Page-DirectoryPointer Table
Physical Addr
PDPTE with PS=1
22
9
40
PML4E
40
CR3
Figure 4-10. Linear-Address Translation to a 1-GByte Page using IA-32e Paging
Vol. 3A 4-21
PAGING
The following items describe the IA-32e paging process in more detail as well has how the page size is determined.
•
A 4-KByte naturally aligned PML4 table is located at the physical address specified in bits 51:12 of CR3 (see
Table 4-12). A PML4 table comprises 512 64-bit entries (PML4Es). A PML4E is selected using the physical
address defined as follows:
— Bits 51:12 are from CR3.
— Bits 11:3 are bits 47:39 of the linear address.
— Bits 2:0 are all 0.
Because a PML4E is identified using bits 47:39 of the linear address, it controls access to a 512-GByte region of
the linear-address space.
•
A 4-KByte naturally aligned page-directory-pointer table is located at the physical address specified in
bits 51:12 of the PML4E (see Table 4-14). A page-directory-pointer table comprises 512 64-bit entries
(PDPTEs). A PDPTE is selected using the physical address defined as follows:
— Bits 51:12 are from the PML4E.
— Bits 11:3 are bits 38:30 of the linear address.
— Bits 2:0 are all 0.
Because a PDPTE is identified using bits 47:30 of the linear address, it controls access to a 1-GByte region of the
linear-address space. Use of the PDPTE depends on its PS flag (bit 7):1
•
If the PDPTE’s PS flag is 1, the PDPTE maps a 1-GByte page (see Table 4-15). The final physical address is
computed as follows:
— Bits 51:30 are from the PDPTE.
— Bits 29:0 are from the original linear address.
•
If the PDE’s PS flag is 0, a 4-KByte naturally aligned page directory is located at the physical address specified
in bits 51:12 of the PDPTE (see Table 4-16). A page directory comprises 512 64-bit entries (PDEs). A PDE is
selected using the physical address defined as follows:
— Bits 51:12 are from the PDPTE.
— Bits 11:3 are bits 29:21 of the linear address.
— Bits 2:0 are all 0.
Because a PDE is identified using bits 47:21 of the linear address, it controls access to a 2-MByte region of the
linear-address space. Use of the PDE depends on its PS flag:
•
If the PDE’s PS flag is 1, the PDE maps a 2-MByte page. The final physical address is computed as shown in
Table 4-17.
— Bits 51:21 are from the PDE.
— Bits 20:0 are from the original linear address.
•
If the PDE’s PS flag is 0, a 4-KByte naturally aligned page table is located at the physical address specified in
bits 51:12 of the PDE (see Table 4-18). A page table comprises 512 64-bit entries (PTEs). A PTE is selected
using the physical address defined as follows:
— Bits 51:12 are from the PDE.
— Bits 11:3 are bits 20:12 of the linear address.
— Bits 2:0 are all 0.
•
Because a PTE is identified using bits 47:12 of the linear address, every PTE maps a 4-KByte page (see
Table 4-19). The final physical address is computed as follows:
— Bits 51:12 are from the PTE.
— Bits 11:0 are from the original linear address.
1. The PS flag of a PDPTE is reserved and must be 0 (if the P flag is 1) if 1-GByte pages are not supported. See Section 4.1.4 for how
to determine whether 1-GByte pages are supported.
4-22 Vol. 3A
PAGING
If a paging-structure entry’s P flag (bit 0) is 0 or if the entry sets any reserved bit, the entry is used neither to reference another paging-structure entry nor to map a page. A reference using a linear address whose translation would
use such a paging-structure entry causes a page-fault exception (see Section 4.7).
The following bits are reserved with IA-32e paging:
•
•
•
•
•
•
If the P flag of a paging-structure entry is 1, bits 51:MAXPHYADDR are reserved.
If the P flag of a PML4E is 1, the PS flag is reserved.
If 1-GByte pages are not supported and the P flag of a PDPTE is 1, the PS flag is reserved.1
If the P flag and the PS flag of a PDPTE are both 1, bits 29:13 are reserved.
If the P flag and the PS flag of a PDE are both 1, bits 20:13 are reserved.
If IA32_EFER.NXE = 0 and the P flag of a paging-structure entry is 1, the XD flag (bit 63) is reserved.
A reference using a linear address that is successfully translated to a physical address is performed only if allowed
by the access rights of the translation; see Section 4.6.
Figure 4-11 gives a summary of the formats of CR3 and the IA-32e paging-structure entries. For the paging structure entries, it identifies separately the format of entries that map pages, those that reference other paging structures, and those that do neither because they are “not present”; bit 0 (P) and bit 7 (PS) are highlighted because
they determine how a paging-structure entry is used.
Table 4-14. Format of an IA-32e PML4 Entry (PML4E) that References a Page-Directory-Pointer Table
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to reference a page-directory-pointer table
1 (R/W)
Read/write; if 0, writes may not be allowed to the 512-GByte region controlled by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 512-GByte region controlled by this entry (see
Section 4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the page-directory-pointer table
referenced by this entry (see Section 4.9.2)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the page-directory-pointer table
referenced by this entry (see Section 4.9.2)
5 (A)
Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)
6
Ignored
7 (PS)
Reserved (must be 0)
11:8
Ignored
M–1:12
Physical address of 4-KByte aligned page-directory-pointer table referenced by this entry
51:M
Reserved (must be 0)
62:52
Ignored
63 (XD)
If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 512-GByte region
controlled by this entry; see Section 4.6); otherwise, reserved (must be 0)
1. See Section 4.1.4 for how to determine whether 1-GByte pages are supported.
Vol. 3A 4-23
PAGING
Table 4-15. Format of an IA-32e Page-Directory-Pointer-Table Entry (PDPTE) that Maps a 1-GByte Page
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to map a 1-GByte page
1 (R/W)
Read/write; if 0, writes may not be allowed to the 1-GByte page referenced by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 1-GByte page referenced by this entry (see Section
4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the 1-GByte page referenced by this
entry (see Section 4.9.2)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the 1-GByte page referenced by this
entry (see Section 4.9.2)
5 (A)
Accessed; indicates whether software has accessed the 1-GByte page referenced by this entry (see Section 4.8)
6 (D)
Dirty; indicates whether software has written to the 1-GByte page referenced by this entry (see Section 4.8)
7 (PS)
Page size; must be 1 (otherwise, this entry references a page directory; see Table 4-16)
8 (G)
Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise
11:9
Ignored
12 (PAT)
Indirectly determines the memory type used to access the 1-GByte page referenced by this entry (see Section
4.9.2)1
29:13
Reserved (must be 0)
(M–1):30
Physical address of the 1-GByte page referenced by this entry
51:M
Reserved (must be 0)
62:52
Ignored
63 (XD)
If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 1-GByte page controlled by
this entry; see Section 4.6); otherwise, reserved (must be 0)
NOTES:
1. The PAT is supported on all processors that support IA-32e paging.
4-24 Vol. 3A
PAGING
Table 4-16. Format of an IA-32e Page-Directory-Pointer-Table Entry (PDPTE) that References a Page Directory
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to reference a page directory
1 (R/W)
Read/write; if 0, writes may not be allowed to the 1-GByte region controlled by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 1-GByte region controlled by this entry (see Section
4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the page directory referenced by
this entry (see Section 4.9.2)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the page directory referenced by
this entry (see Section 4.9.2)
5 (A)
Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)
6
Ignored
7 (PS)
Page size; must be 0 (otherwise, this entry maps a 1-GByte page; see Table 4-15)
11:8
Ignored
(M–1):12
Physical address of 4-KByte aligned page directory referenced by this entry
51:M
Reserved (must be 0)
62:52
Ignored
63 (XD)
If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 1-GByte region controlled
by this entry; see Section 4.6); otherwise, reserved (must be 0)
Table 4-17. Format of an IA-32e Page-Directory Entry that Maps a 2-MByte Page
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to map a 2-MByte page
1 (R/W)
Read/write; if 0, writes may not be allowed to the 2-MByte page referenced by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 2-MByte page referenced by this entry (see Section
4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the 2-MByte page referenced by
this entry (see Section 4.9.2)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the 2-MByte page referenced by
this entry (see Section 4.9.2)
5 (A)
Accessed; indicates whether software has accessed the 2-MByte page referenced by this entry (see Section 4.8)
6 (D)
Dirty; indicates whether software has written to the 2-MByte page referenced by this entry (see Section 4.8)
7 (PS)
Page size; must be 1 (otherwise, this entry references a page table; see Table 4-18)
8 (G)
Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise
Vol. 3A 4-25
PAGING
Table 4-17. Format of an IA-32e Page-Directory Entry that Maps a 2-MByte Page (Contd.)
Bit
Position(s)
Contents
11:9
Ignored
12 (PAT)
Indirectly determines the memory type used to access the 2-MByte page referenced by this entry (see Section
4.9.2)
20:13
Reserved (must be 0)
(M–1):21
Physical address of the 2-MByte page referenced by this entry
51:M
Reserved (must be 0)
62:52
Ignored
63 (XD)
If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 2-MByte page controlled by
this entry; see Section 4.6); otherwise, reserved (must be 0)
Table 4-18. Format of an IA-32e Page-Directory Entry that References a Page Table
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to reference a page table
1 (R/W)
Read/write; if 0, writes may not be allowed to the 2-MByte region controlled by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 2-MByte region controlled by this entry (see Section
4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9.2)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9.2)
5 (A)
Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)
6
Ignored
7 (PS)
Page size; must be 0 (otherwise, this entry maps a 2-MByte page; see Table 4-17)
11:8
Ignored
(M–1):12
Physical address of 4-KByte aligned page table referenced by this entry
51:M
Reserved (must be 0)
62:52
Ignored
63 (XD)
If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 2-MByte region controlled
by this entry; see Section 4.6); otherwise, reserved (must be 0)
4-26 Vol. 3A
PAGING
Table 4-19. Format of an IA-32e Page-Table Entry that Maps a 4-KByte Page
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to map a 4-KByte page
1 (R/W)
Read/write; if 0, writes may not be allowed to the 4-KByte page referenced by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 4-KByte page referenced by this entry (see Section
4.6)
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the 4-KByte page referenced by
this entry (see Section 4.9.2)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9.2)
5 (A)
Accessed; indicates whether software has accessed the 4-KByte page referenced by this entry (see Section 4.8)
6 (D)
Dirty; indicates whether software has written to the 4-KByte page referenced by this entry (see Section 4.8)
7 (PAT)
Indirectly determines the memory type used to access the 4-KByte page referenced by this entry (see Section 4.9.2)
8 (G)
Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise
11:9
Ignored
(M–1):12
Physical address of the 4-KByte page referenced by this entry
51:M
Reserved (must be 0)
62:52
Ignored
63 (XD)
If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 4-KByte page controlled by
this entry; see Section 4.6); otherwise, reserved (must be 0)
Vol. 3A 4-27
PAGING
.
6666555555555
3210987654321
M1 M-1
33322222222221111111111
210987654321098765432109876543210
Reserved2
X
D
3
Ignored
Address of PML4 table
Rsvd.
Ignored
Address of page-directory-pointer table
Ign.
PP
C W Ign.
DT
PUR
Rs gI A P
PML4E:
C
W
/ 1 present
vd n D T /S W
0
PML4E:
not
present
P
PPUR
A Ign. G 1 D A C W /S
/ 1
T
DT W
PDPTE:
1GB
page
Ignored
X
D
Ignored
Rsvd.
X
D
Ignored
Rsvd.
Address of
1GB page frame
Reserved
Address of page directory
Ign.
I PPUR
PDPTE:
page
0 g A C W /S / 1
n DT W
directory
Ignored
X
D
Ignored
Rsvd.
X
D
Ignored
Rsvd.
Address of
2MB page frame
0
Reserved
Address of page table
Ignored
Rsvd.
Address of 4KB page frame
PDTPE:
not
present
PPUR
P
A Ign. G 1 D A C W /S / 1
DT W
T
PDE:
2MB
page
I PPUR
0 g A C W /S / 1
n DT W
PDE:
page
table
Ign.
Ignored
X
D
CR3
0
P
PPUR
Ign. G A D A C W /S
/ 1
T
DT W
Ignored
0
PDE:
not
present
PTE:
4KB
page
PTE:
not
present
Figure 4-11. Formats of CR3 and Paging-Structure Entries with IA-32e Paging
NOTES:
1. M is an abbreviation for MAXPHYADDR.
2. Reserved fields must be 0.
3. If IA32_EFER.NXE = 0 and the P flag of a paging-structure entry is 1, the XD flag (bit 63) is reserved.
4.6
ACCESS RIGHTS
There is a translation for a linear address if the processes described in Section 4.3, Section 4.4.2, and Section 4.5
(depending upon the paging mode) completes and produces a physical address. Whether an access is permitted by
a translation is determined by the access rights specified by the paging-structure entries controlling the translation;1 paging-mode modifiers in CR0, CR4, and the IA32_EFERMSR; and the mode of the access.
1. With PAE paging, the PDPTEs do not determine access rights.
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PAGING
Every access to a linear address is either a supervisor-mode access or a user-mode access. All accesses
performed while the current privilege level (CPL) is less than 3 are supervisor-mode accesses. If CPL = 3, accesses
are generally user-mode accesses. However, some operations implicitly access system data structures with linear
addresses; the resulting accesses to those data structures are supervisor-mode accesses regardless of CPL. Examples of such implicit supervisor accesses include the following: accesses to the global descriptor table (GDT) or
local descriptor table (LDT) to load a segment descriptor; accesses to the interrupt descriptor table (IDT) when
delivering an interrupt or exception; and accesses to the task-state segment (TSS) as part of a task switch or
change of CPL.
The following items detail how paging determines access rights:
•
For supervisor-mode accesses:
— Data reads.
Data may be read from any linear address with a valid translation.
— Data writes.
•
•
If CR0.WP = 0, data may be written to any linear address with a valid translation.
If CR0.WP = 1, data may be written to any linear address with a valid translation for which the R/W flag
(bit 1) is 1 in every paging-structure entry controlling the translation.
— Instruction fetches.
•
•
•
For 32-bit paging or if IA32_EFER.NXE = 0, access rights depend on the value of CR4.SMEP:
—
If CR4.SMEP = 0, instructions may be fetched from any linear address with a valid translation.
—
If CR4.SMEP = 1, instructions may be fetched from any linear address with a valid translation for
which the U/S flag (bit 2) is 0 in at least one of the paging-structure entries controlling the translation.
For PAE paging or IA-32e paging with IA32_EFER.NXE = 1, access rights depend on the value of
CR4.SMEP:
—
If CR4.SMEP = 0, instructions may be fetched from any linear address with a valid translation for
which the XD flag (bit 63) is 0 in every paging-structure entry controlling the translation.
—
If CR4.SMEP = 1, instructions may be fetched from any linear address with a valid translation for
which (1) the U/S flag is 0 in at least one of the paging-structure entries controlling the translation;
and (2) the XD flag is 0 in every paging-structure entry controlling the translation.
For user-mode accesses:
— Data reads.
Data may be read from any linear address with a valid translation for which the U/S flag (bit 2) is 1 in every
paging-structure entry controlling the translation.
— Data writes.
Data may be written to any linear address with a valid translation for which both the R/W flag and the U/S
flag are 1 in every paging-structure entry controlling the translation.
— Instruction fetches.
•
For 32-bit paging or if IA32_EFER.NXE = 0, instructions may be fetched from any linear address with a
valid translation for which the U/S flag is 1 in every paging-structure entry controlling the translation.
•
For PAE paging or IA-32e paging with IA32_EFER.NXE = 1, instructions may be fetched from any linear
address with a valid translation for which the U/S flag is 1 and the XD flag is 0 in every paging-structure
entry controlling the translation.
A processor may cache information from the paging-structure entries in TLBs and paging-structure caches (see
Section 4.10). These structures may include information about access rights. The processor may enforce access
rights based on the TLBs and paging-structure caches instead of on the paging structures in memory.
This fact implies that, if software modifies a paging-structure entry to change access rights, the processor might
not use that change for a subsequent access to an affected linear address (see Section 4.10.4.3). See Section
4.10.4.2 for how software can ensure that the processor uses the modified access rights.
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4.7
PAGE-FAULT EXCEPTIONS
Accesses using linear addresses may cause page-fault exceptions (#PF; exception 14). An access to a linear
address may cause page-fault exception for either of two reasons: (1) there is no valid translation for the linear
address; or (2) there is a valid translation for the linear address, but its access rights do not permit the access.
As noted in Section 4.3, Section 4.4.2, and Section 4.5, there is no valid translation for a linear address if the translation process for that address would use a paging-structure entry in which the P flag (bit 0) is 0 or one that sets a
reserved bit. If there is a valid translation for a linear address, its access rights are determined as specified in
Section 4.6.
Figure 4-12 illustrates the error code that the processor provides on delivery of a page-fault exception. The
following items explain how the bits in the error code describe the nature of the page-fault exception:
4 3 2 1 0
31
P
W/R
U/S
RSVD
I/D
Reserved
P
0 The fault was caused by a non-present page.
1 The fault was caused by a page-level protection violation.
W/R
0 The access causing the fault was a read.
1 The access causing the fault was a write.
U/S
0 A supervisor-mode access caused the fault.
1 A user-mode access caused the fault.
RSVD
0 The fault was not caused by reserved bit violation.
1 The fault was caused by a reserved bit set to 1 in some
paging-structure entry.
I/D
0 The fault was not caused by an instruction fetch.
1 The fault was caused by an instruction fetch.
Figure 4-12. Page-Fault Error Code
•
P flag (bit 0).
This flag is 0 if there is no valid translation for the linear address because the P flag was 0 in one of the pagingstructure entries used to translate that address.
•
W/R (bit 1).
If the access causing the page-fault exception was a write, this flag is 1; otherwise, it is 0. This flag describes
the access causing the page-fault exception, not the access rights specified by paging.
•
U/S (bit 2).
If a user-mode access caused the page-fault exception, this flag is 1; it is 0 if a supervisor-mode access did so.
This flag describes the access causing the page-fault exception, not the access rights specified by paging. Usermode and supervisor-mode accesses are defined in Section 4.6.
•
RSVD flag (bit 3).
This flag is 1 if there is no valid translation for the linear address because a reserved bit was set in one of the
paging-structure entries used to translate that address. (Because reserved bits are not checked in a pagingstructure entry whose P flag is 0, bit 3 of the error code can be set only if bit 0 is also set.)
Bits reserved in the paging-structure entries are reserved for future functionality. Software developers should
be aware that such bits may be used in the future and that a paging-structure entry that causes a page-fault
exception on one processor might not do so in the future.
•
I/D flag (bit 4).
This flag is 1 if (1) the access causing the page-fault exception was an instruction fetch; and (2) either
(a) CR4.SMEP = 1; or (b) both (i) CR4.PAE = 1 (either PAE paging or IA-32e paging is in use); and
(ii) IA32_EFER.NXE = 1. Otherwise, the flag is 0. This flag describes the access causing the page-fault
exception, not the access rights specified by paging.
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PAGING
Page-fault exceptions occur only due to an attempt to use a linear address. Failures to load the PDPTE registers
with PAE paging (see Section 4.4.1) cause general-protection exceptions (#GP(0)) and not page-fault exceptions.
4.8
ACCESSED AND DIRTY FLAGS
For any paging-structure entry that is used during linear-address translation, bit 5 is the accessed flag.1 For
paging-structure entries that map a page (as opposed to referencing another paging structure), bit 6 is the dirty
flag. These flags are provided for use by memory-management software to manage the transfer of pages and
paging structures into and out of physical memory.
Whenever the processor uses a paging-structure entry as part of linear-address translation, it sets the accessed
flag in that entry (if it is not already set).
Whenever there is a write to a linear address, the processor sets the dirty flag (if it is not already set) in the pagingstructure entry that identifies the final physical address for the linear address (either a PTE or a paging-structure
entry in which the PS flag is 1).
Memory-management software may clear these flags when a page or a paging structure is initially loaded into
physical memory. These flags are “sticky,” meaning that, once set, the processor does not clear them; only software can clear them.
A processor may cache information from the paging-structure entries in TLBs and paging-structure caches (see
Section 4.10). This fact implies that, if software changes an accessed flag or a dirty flag from 1 to 0, the processor
might not set the corresponding bit in memory on a subsequent access using an affected linear address (see
Section 4.10.4.3). See Section 4.10.4.2 for how software can ensure that these bits are updated as desired.
NOTE
The accesses used by the processor to set these flags may or may not be exposed to the
processor’s self-modifying code detection logic. If the processor is executing code from the same
memory area that is being used for the paging structures, the setting of these flags may or may not
result in an immediate change to the executing code stream.
4.9
PAGING AND MEMORY TYPING
The memory type of a memory access refers to the type of caching used for that access. Chapter 11, “Memory
Cache Control” provides many details regarding memory typing in the Intel-64 and IA-32 architectures. This
section describes how paging contributes to the determination of memory typing.
The way in which paging contributes to memory typing depends on whether the processor supports the Page
Attribute Table (PAT; see Section 11.12).2 Section 4.9.1 and Section 4.9.2 explain how paging contributes to
memory typing depending on whether the PAT is supported.
4.9.1
Paging and Memory Typing When the PAT is Not Supported (Pentium Pro and
Pentium II Processors)
NOTE
The PAT is supported on all processors that support IA-32e paging. Thus, this section applies only
to 32-bit paging and PAE paging.
1. With PAE paging, the PDPTEs are not used during linear-address translation but only to load the PDPTE registers for some executions of the MOV CR instruction (see Section 4.4.1). For this reason, the PDPTEs do not contain accessed flags with PAE paging.
2. The PAT is supported on Pentium III and more recent processor families. See Section 4.1.4 for how to determine whether the PAT is
supported.
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PAGING
If the PAT is not supported, paging contributes to memory typing in conjunction with the memory-type range registers (MTRRs) as specified in Table 11-6 in Section 11.5.2.1.
For any access to a physical address, the table combines the memory type specified for that physical address by
the MTRRs with a PCD value and a PWT value. The latter two values are determined as follows:
•
•
•
•
For an access to a PDE with 32-bit paging, the PCD and PWT values come from CR3.
•
With PAE paging, the UC memory type is used when loading the PDPTEs (see Section 4.4.1).
For an access to a PDE with PAE paging, the PCD and PWT values come from the relevant PDPTE register.
For an access to a PTE, the PCD and PWT values come from the relevant PDE.
For an access to the physical address that is the translation of a linear address, the PCD and PWT values come
from the relevant PTE (if the translation uses a 4-KByte page) or the relevant PDE (otherwise).
4.9.2
Paging and Memory Typing When the PAT is Supported (Pentium III and More Recent
Processor Families)
If the PAT is supported, paging contributes to memory typing in conjunction with the PAT and the memory-type
range registers (MTRRs) as specified in Table 11-7 in Section 11.5.2.2.
The PAT is a 64-bit MSR (IA32_PAT; MSR index 277H) comprising eight (8) 8-bit entries (entry i comprises
bits 8i+7:8i of the MSR).
For any access to a physical address, the table combines the memory type specified for that physical address by
the MTRRs with a memory type selected from the PAT. Table 11-11 in Section 11.12.3 specifies how a memory type
is selected from the PAT. Specifically, it comes from entry i of the PAT, where i is defined as follows:
•
For an access to an entry in a paging structure whose address is in CR3 (e.g., the PML4 table with IA-32e
paging):
— For IA-32e paging with CR4.PCIDE = 1, i = 0.
— Otherwise, i = 2*PCD+PWT, where the PCD and PWT values come from CR3.
•
For an access to a PDE with PAE paging, i = 2*PCD+PWT, where the PCD and PWT values come from the
relevant PDPTE register.
•
For an access to a paging-structure entry X whose address is in another paging-structure entry Y, i =
2*PCD+PWT, where the PCD and PWT values come from Y.
•
For an access to the physical address that is the translation of a linear address, i = 4*PAT+2*PCD+PWT, where
the PAT, PCD, and PWT values come from the relevant PTE (if the translation uses a 4-KByte page), the relevant
PDE (if the translation uses a 2-MByte page or a 4-MByte page), or the relevant PDPTE (if the translation uses
a 1-GByte page).
•
With PAE paging, the WB memory type is used when loading the PDPTEs (see Section 4.4.1).1
4.9.3
Caching Paging-Related Information about Memory Typing
A processor may cache information from the paging-structure entries in TLBs and paging-structure caches (see
Section 4.10). These structures may include information about memory typing. The processor may use memorytyping information from the TLBs and paging-structure caches instead of from the paging structures in memory.
This fact implies that, if software modifies a paging-structure entry to change the memory-typing bits, the
processor might not use that change for a subsequent translation using that entry or for access to an affected linear
address. See Section 4.10.4.2 for how software can ensure that the processor uses the modified memory typing.
1. Some older IA-32 processors used the UC memory type when loading the PDPTEs. Some processors may use the UC memory type if
CR0.CD = 1 or if the MTRRs are disabled. These behaviors are model-specific and not architectural.
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4.10
CACHING TRANSLATION INFORMATION
The Intel-64 and IA-32 architectures may accelerate the address-translation process by caching data from the
paging structures on the processor. Because the processor does not ensure that the data that it caches are always
consistent with the structures in memory, it is important for software developers to understand how and when the
processor may cache such data. They should also understand what actions software can take to remove cached
data that may be inconsistent and when it should do so. This section provides software developers information
about the relevant processor operation.
Section 4.10.1 introduces process-context identifiers (PCIDs), which a logical processor may use to distinguish
information cached for different linear-address spaces. Section 4.10.2 and Section 4.10.3 describe how the
processor may cache information in translation lookaside buffers (TLBs) and paging-structure caches, respectively.
Section 4.10.4 explains how software can remove inconsistent cached information by invalidating portions of the
TLBs and paging-structure caches. Section 4.10.5 describes special considerations for multiprocessor systems.
4.10.1
Process-Context Identifiers (PCIDs)
Process-context identifiers (PCIDs) are a facility by which a logical processor may cache information for multiple
linear-address spaces. The processor may retain cached information when software switches to a different linearaddress space with a different PCID (e.g., by loading CR3; see Section 4.10.4.1 for details).
A PCID is a 12-bit identifier. Non-zero PCIDs are enabled by setting the PCIDE flag (bit 17) of CR4. If CR4.PCIDE =
0, the current PCID is always 000H; otherwise, the current PCID is the value of bits 11:0 of CR3. Not all processors
allow CR4.PCIDE to be set to 1; see Section 4.1.4 for how to determine whether this is allowed.
The processor ensures that CR4.PCIDE can be 1 only in IA-32e mode (thus, 32-bit paging and PAE paging use only
PCID 000H). In addition, software can change CR4.PCIDE from 0 to 1 only if CR3[11:0] = 000H. These requirements are enforced by the following limitations on the MOV CR instruction:
•
MOV to CR4 causes a general-protection exception (#GP) if it would change CR4.PCIDE from 0 to 1 and either
IA32_EFER.LMA = 0 or CR3[11:0] ≠ 000H.
•
MOV to CR0 causes a general-protection exception if it would clear CR0.PG to 0 while CR4.PCIDE = 1.
When a logical processor creates entries in the TLBs (Section 4.10.2) and paging-structure caches (Section
4.10.3), it associates those entries with the current PCID. When using entries in the TLBs and paging-structure
caches to translate a linear address, a logical processor uses only those entries associated with the current PCID
(see Section 4.10.2.4 for an exception).
If CR4.PCIDE = 0, a logical processor does not cache information for any PCID other than 000H. This is because
(1) if CR4.PCIDE = 0, the logical processor will associate any newly cached information with the current PCID,
000H; and (2) if MOV to CR4 clears CR4.PCIDE, all cached information is invalidated (see Section 4.10.4.1).
NOTE
In revisions of this manual that were produced when no processors allowed CR4.PCIDE to be set to
1, Section 4.10 discussed the caching of translation information without any reference to PCIDs.
While the section now refers to PCIDs in its specification of this caching, this documentation change
is not intended to imply any change to the behavior of processors that do not allow CR4.PCIDE to
be set to 1.
4.10.2
Translation Lookaside Buffers (TLBs)
A processor may cache information about the translation of linear addresses in translation lookaside buffers
(TLBs). In general, TLBs contain entries that map page numbers to page frames; these terms are defined in
Section 4.10.2.1. Section 4.10.2.2 describes how information may be cached in TLBs, and Section 4.10.2.3 gives
details of TLB usage. Section 4.10.2.4 explains the global-page feature, which allows software to indicate that
certain translations should receive special treatment when cached in the TLBs.
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4.10.2.1
Page Numbers, Page Frames, and Page Offsets
Section 4.3, Section 4.4.2, and Section 4.5 give details of how the different paging modes translate linear
addresses to physical addresses. Specifically, the upper bits of a linear address (called the page number) determine the upper bits of the physical address (called the page frame); the lower bits of the linear address (called the
page offset) determine the lower bits of the physical address. The boundary between the page number and the
page offset is determined by the page size. Specifically:
•
32-bit paging:
— If the translation does not use a PTE (because CR4.PSE = 1 and the PS flag is 1 in the PDE used), the page
size is 4 MBytes and the page number comprises bits 31:22 of the linear address.
— If the translation does use a PTE, the page size is 4 KBytes and the page number comprises bits 31:12 of
the linear address.
•
PAE paging:
— If the translation does not use a PTE (because the PS flag is 1 in the PDE used), the page size is 2 MBytes
and the page number comprises bits 31:21 of the linear address.
— If the translation does uses a PTE, the page size is 4 KBytes and the page number comprises bits 31:12 of
the linear address.
•
IA-32e paging:
— If the translation does not use a PDE (because the PS flag is 1 in the PDPTE used), the page size is 1 GBytes
and the page number comprises bits 47:30 of the linear address.
— If the translation does use a PDE but does not uses a PTE (because the PS flag is 1 in the PDE used), the
page size is 2 MBytes and the page number comprises bits 47:21 of the linear address.
— If the translation does use a PTE, the page size is 4 KBytes and the page number comprises bits 47:12 of
the linear address.
4.10.2.2
Caching Translations in TLBs
The processor may accelerate the paging process by caching individual translations in translation lookaside
buffers (TLBs). Each entry in a TLB is an individual translation. Each translation is referenced by a page number.
It contains the following information from the paging-structure entries used to translate linear addresses with the
page number:
•
•
The physical address corresponding to the page number (the page frame).
The access rights from the paging-structure entries used to translate linear addresses with the page number
(see Section 4.6):
— The logical-AND of the R/W flags.
— The logical-AND of the U/S flags.
— The logical-OR of the XD flags (necessary only if IA32_EFER.NXE = 1).
•
Attributes from a paging-structure entry that identifies the final page frame for the page number (either a PTE
or a paging-structure entry in which the PS flag is 1):
— The dirty flag (see Section 4.8).
— The memory type (see Section 4.9).
(TLB entries may contain other information as well. A processor may implement multiple TLBs, and some of these
may be for special purposes, e.g., only for instruction fetches. Such special-purpose TLBs may not contain some of
this information if it is not necessary. For example, a TLB used only for instruction fetches need not contain information about the R/W and dirty flags.)
As noted in Section 4.10.1, any TLB entries created by a logical processor are associated with the current PCID.
Processors need not implement any TLBs. Processors that do implement TLBs may invalidate any TLB entry at any
time. Software should not rely on the existence of TLBs or on the retention of TLB entries.
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4.10.2.3
Details of TLB Use
Because the TLBs cache only valid translations, there can be a TLB entry for a page number only if the P flag is 1
and the reserved bits are 0 in each of the paging-structure entries used to translate that page number. In addition,
the processor does not cache a translation for a page number unless the accessed flag is 1 in each of the pagingstructure entries used during translation; before caching a translation, the processor sets any of these accessed
flags that is not already 1.
The processor may cache translations required for prefetches and for accesses that are a result of speculative
execution that would never actually occur in the executed code path.
If the page number of a linear address corresponds to a TLB entry associated with the current PCID, the processor
may use that TLB entry to determine the page frame, access rights, and other attributes for accesses to that linear
address. In this case, the processor may not actually consult the paging structures in memory. The processor may
retain a TLB entry unmodified even if software subsequently modifies the relevant paging-structure entries in
memory. See Section 4.10.4.2 for how software can ensure that the processor uses the modified paging-structure
entries.
If the paging structures specify a translation using a page larger than 4 KBytes, some processors may choose to
cache multiple smaller-page TLB entries for that translation. Each such TLB entry would be associated with a page
number corresponding to the smaller page size (e.g., bits 47:12 of a linear address with IA-32e paging), even
though part of that page number (e.g., bits 20:12) are part of the offset with respect to the page specified by the
paging structures. The upper bits of the physical address in such a TLB entry are derived from the physical address
in the PDE used to create the translation, while the lower bits come from the linear address of the access for which
the translation is created. There is no way for software to be aware that multiple translations for smaller pages
have been used for a large page.
If software modifies the paging structures so that the page size used for a 4-KByte range of linear addresses
changes, the TLBs may subsequently contain multiple translations for the address range (one for each page size).
A reference to a linear address in the address range may use any of these translations. Which translation is used
may vary from one execution to another, and the choice may be implementation-specific.
4.10.2.4
Global Pages
The Intel-64 and IA-32 architectures also allow for global pages when the PGE flag (bit 7) is 1 in CR4. If the G flag
(bit 8) is 1 in a paging-structure entry that maps a page (either a PTE or a paging-structure entry in which the PS
flag is 1), any TLB entry cached for a linear address using that paging-structure entry is considered to be global.
Because the G flag is used only in paging-structure entries that map a page, and because information from such
entries are not cached in the paging-structure caches, the global-page feature does not affect the behavior of the
paging-structure caches.
A logical processor may use a global TLB entry to translate a linear address, even if the TLB entry is associated with
a PCID different from the current PCID.
4.10.3
Paging-Structure Caches
In addition to the TLBs, a processor may cache other information about the paging structures in memory.
4.10.3.1
Caches for Paging Structures
A processor may support any or of all the following paging-structure caches:
•
PML4 cache (IA-32e paging only). Each PML4-cache entry is referenced by a 9-bit value and is used for linear
addresses for which bits 47:39 have that value. The entry contains information from the PML4E used to
translate such linear addresses:
— The physical address from the PML4E (the address of the page-directory-pointer table).
— The value of the R/W flag of the PML4E.
— The value of the U/S flag of the PML4E.
— The value of the XD flag of the PML4E.
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— The values of the PCD and PWT flags of the PML4E.
The following items detail how a processor may use the PML4 cache:
— If the processor has a PML4-cache entry for a linear address, it may use that entry when translating the
linear address (instead of the PML4E in memory).
— The processor does not create a PML4-cache entry unless the P flag is 1 and all reserved bits are 0 in the
PML4E in memory.
— The processor does not create a PML4-cache entry unless the accessed flag is 1 in the PML4E in memory;
before caching a translation, the processor sets the accessed flag if it is not already 1.
— The processor may create a PML4-cache entry even if there are no translations for any linear address that
might use that entry (e.g., because the P flags are 0 in all entries in the referenced page-directory-pointer
table).
— If the processor creates a PML4-cache entry, the processor may retain it unmodified even if software subsequently modifies the corresponding PML4E in memory.
•
PDPTE cache (IA-32e paging only).1 Each PDPTE-cache entry is referenced by an 18-bit value and is used for
linear addresses for which bits 47:30 have that value. The entry contains information from the PML4E and
PDPTE used to translate such linear addresses:
— The physical address from the PDPTE (the address of the page directory). (No PDPTE-cache entry is created
for a PDPTE that maps a 1-GByte page.)
— The logical-AND of the R/W flags in the PML4E and the PDPTE.
— The logical-AND of the U/S flags in the PML4E and the PDPTE.
— The logical-OR of the XD flags in the PML4E and the PDPTE.
— The values of the PCD and PWT flags of the PDPTE.
The following items detail how a processor may use the PDPTE cache:
— If the processor has a PDPTE-cache entry for a linear address, it may use that entry when translating the
linear address (instead of the PML4E and the PDPTE in memory).
— The processor does not create a PDPTE-cache entry unless the P flag is 1, the PS flag is 0, and the reserved
bits are 0 in the PML4E and the PDPTE in memory.
— The processor does not create a PDPTE-cache entry unless the accessed flags are 1 in the PML4E and the
PDPTE in memory; before caching a translation, the processor sets any accessed flags that are not already
1.
— The processor may create a PDPTE-cache entry even if there are no translations for any linear address that
might use that entry.
— If the processor creates a PDPTE-cache entry, the processor may retain it unmodified even if software
subsequently modifies the corresponding PML4E or PDPTE in memory.
•
PDE cache. The use of the PDE cache depends on the paging mode:
— For 32-bit paging, each PDE-cache entry is referenced by a 10-bit value and is used for linear addresses for
which bits 31:22 have that value.
— For PAE paging, each PDE-cache entry is referenced by an 11-bit value and is used for linear addresses for
which bits 31:21 have that value.
— For IA-32e paging, each PDE-cache entry is referenced by a 27-bit value and is used for linear addresses for
which bits 47:21 have that value.
A PDE-cache entry contains information from the PML4E, PDPTE, and PDE used to translate the relevant linear
addresses (for 32-bit paging and PAE paging, only the PDE applies):
— The physical address from the PDE (the address of the page table). (No PDE-cache entry is created for a
PDE that maps a page.)
1. With PAE paging, the PDPTEs are stored in internal, non-architectural registers. The operation of these registers is described in Section 4.4.1 and differs from that described here.
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— The logical-AND of the R/W flags in the PML4E, PDPTE, and PDE.
— The logical-AND of the U/S flags in the PML4E, PDPTE, and PDE.
— The logical-OR of the XD flags in the PML4E, PDPTE, and PDE.
— The values of the PCD and PWT flags of the PDE.
The following items detail how a processor may use the PDE cache (references below to PML4Es and PDPTEs
apply on to IA-32e paging):
— If the processor has a PDE-cache entry for a linear address, it may use that entry when translating the
linear address (instead of the PML4E, the PDPTE, and the PDE in memory).
— The processor does not create a PDE-cache entry unless the P flag is 1, the PS flag is 0, and the reserved
bits are 0 in the PML4E, the PDPTE, and the PDE in memory.
— The processor does not create a PDE-cache entry unless the accessed flag is 1 in the PML4E, the PDPTE,
and the PDE in memory; before caching a translation, the processor sets any accessed flags that are not
already 1.
— The processor may create a PDE-cache entry even if there are no translations for any linear address that
might use that entry.
— If the processor creates a PDE-cache entry, the processor may retain it unmodified even if software subsequently modifies the corresponding PML4E, the PDPTE, or the PDE in memory.
Information from a paging-structure entry can be included in entries in the paging-structure caches for other
paging-structure entries referenced by the original entry. For example, if the R/W flag is 0 in a PML4E, then the R/W
flag will be 0 in any PDPTE-cache entry for a PDPTE from the page-directory-pointer table referenced by that
PML4E. This is because the R/W flag of each such PDPTE-cache entry is the logical-AND of the R/W flags in the
appropriate PML4E and PDPTE.
The paging-structure caches contain information only from paging-structure entries that reference other paging
structures (and not those that map pages). Because the G flag is not used in such paging-structure entries, the
global-page feature does not affect the behavior of the paging-structure caches.
The processor may create entries in paging-structure caches for translations required for prefetches and for
accesses that are a result of speculative execution that would never actually occur in the executed code path.
As noted in Section 4.10.1, any entries created in paging-structure caches by a logical processor are associated
with the current PCID.
A processor may or may not implement any of the paging-structure caches. Software should rely on neither their
presence nor their absence. The processor may invalidate entries in these caches at any time. Because the
processor may create the cache entries at the time of translation and not update them following subsequent modifications to the paging structures in memory, software should take care to invalidate the cache entries appropriately when causing such modifications. The invalidation of TLBs and the paging-structure caches is described in
Section 4.10.4.
4.10.3.2
Using the Paging-Structure Caches to Translate Linear Addresses
When a linear address is accessed, the processor uses a procedure such as the following to determine the physical
address to which it translates and whether the access should be allowed:
•
If the processor finds a TLB entry that is for the page number of the linear address and that is associated with
the current PCID (or which is global), it may use the physical address, access rights, and other attributes from
that entry.
•
If the processor does not find a relevant TLB entry, it may use the upper bits of the linear address to select an
entry from the PDE cache that is associated with the current PCID (Section 4.10.3.1 indicates which bits are
used in each paging mode). It can then use that entry to complete the translation process (locating a PTE, etc.)
as if it had traversed the PDE (and, for IA-32e paging, the PDPTE and PML4) corresponding to the PDE-cache
entry.
•
The following items apply when IA-32e paging is used:
— If the processor does not find a relevant TLB entry or a relevant PDE-cache entry, it may use bits 47:30 of
the linear address to select an entry from the PDPTE cache that is associated with the current PCID. It can
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then use that entry to complete the translation process (locating a PDE, etc.) as if it had traversed the
PDPTE and the PML4 corresponding to the PDPTE-cache entry.
— If the processor does not find a relevant TLB entry, a relevant PDE-cache entry, or a relevant PDPTE-cache
entry, it may use bits 47:39 of the linear address to select an entry from the PML4 cache that is associated
with the current PCID. It can then use that entry to complete the translation process (locating a PDPTE,
etc.) as if it had traversed the corresponding PML4.
(Any of the above steps would be skipped if the processor does not support the cache in question.)
If the processor does not find a TLB or paging-structure-cache entry for the linear address, it uses the linear
address to traverse the entire paging-structure hierarchy, as described in Section 4.3, Section 4.4.2, and Section
4.5.
4.10.3.3
Multiple Cached Entries for a Single Paging-Structure Entry
The paging-structure caches and TLBs and paging-structure caches may contain multiple entries associated with a
single PCID and with information derived from a single paging-structure entry. The following items give some
examples for IA-32e paging:
•
Suppose that two PML4Es contain the same physical address and thus reference the same page-directorypointer table. Any PDPTE in that table may result in two PDPTE-cache entries, each associated with a different
set of linear addresses. Specifically, suppose that the n1th and n2th entries in the PML4 table contain the same
physical address. This implies that the physical address in the mth PDPTE in the page-directory-pointer table
would appear in the PDPTE-cache entries associated with both p1 and p2, where (p1 » 9) = n1, (p2 » 9) = n2,
and (p1 & 1FFH) = (p2 & 1FFH) = m. This is because both PDPTE-cache entries use the same PDPTE, one
resulting from a reference from the n1th PML4E and one from the n2th PML4E.
•
Suppose that the first PML4E (i.e., the one in position 0) contains the physical address X in CR3 (the physical
address of the PML4 table). This implies the following:
— Any PML4-cache entry associated with linear addresses with 0 in bits 47:39 contains address X.
— Any PDPTE-cache entry associated with linear addresses with 0 in bits 47:30 contains address X. This is
because the translation for a linear address for which the value of bits 47:30 is 0 uses the value of
bits 47:39 (0) to locate a page-directory-pointer table at address X (the address of the PML4 table). It then
uses the value of bits 38:30 (also 0) to find address X again and to store that address in the PDPTE-cache
entry.
— Any PDE-cache entry associated with linear addresses with 0 in bits 47:21 contains address X for similar
reasons.
— Any TLB entry for page number 0 (associated with linear addresses with 0 in bits 47:12) translates to page
frame X » 12 for similar reasons.
The same PML4E contributes its address X to all these cache entries because the self-referencing nature of the
entry causes it to be used as a PML4E, a PDPTE, a PDE, and a PTE.
4.10.4
Invalidation of TLBs and Paging-Structure Caches
As noted in Section 4.10.2 and Section 4.10.3, the processor may create entries in the TLBs and the paging-structure caches when linear addresses are translated, and it may retain these entries even after the paging structures
used to create them have been modified. To ensure that linear-address translation uses the modified paging structures, software should take action to invalidate any cached entries that may contain information that has since
been modified.
4.10.4.1
Operations that Invalidate TLBs and Paging-Structure Caches
The following instructions invalidate entries in the TLBs and the paging-structure caches:
•
INVLPG. This instruction takes a single operand, which is a linear address. The instruction invalidates any TLB
entries that are for a page number corresponding to the linear address and that are associated with the current
PCID. It also invalidates any global TLB entries with that page number, regardless of PCID (see Section
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4.10.2.4).1 INVLPG also invalidates all entries in all paging-structure caches associated with the current PCID,
regardless of the linear addresses to which they correspond.
•
INVPCID. The operation of this instruction is based on instruction operands, called the INVPCID type and the
INVPCID descriptor. Four INVPCID types are currently defined:
— Individual-address. If the INVPCID type is 0, the logical processor invalidates mappings—except global
translations—associated with the PCID specified in the INVPCID descriptor and that would be used to
translate the linear address specified in the INVPCID descriptor. (The instruction may also invalidate global
translations, as well as mappings associated with other PCIDs and for other linear addresses.)
— Single-context. If the INVPCID type is 1, the logical processor invalidates all mappings—except global
translations—associated with the PCID specified in the INVPCID descriptor. (The instruction may also
invalidate global translations, as well as mappings associated with other PCIDs.)
— All-context, including globals. If the INVPCID type is 2, the logical processor invalidates
mappings—including global translations—associated with all PCIDs.
— All-context. If the INVPCID type is 3, the logical processor invalidates mappings—except global translations—associated with all PCIDs. (The instruction may also invalidate global translations.)
See Chapter 3 of the Intel 64 and IA-32 Architecture Software Developer’s Manual, Volume 2A for details of the
INVPCID instruction.
•
MOV to CR0. The instruction invalidates all TLB entries (including global entries) and all entries in all pagingstructure caches (for all PCIDs) if it changes the value of CR0.PG from 1 to 0.
•
MOV to CR3. The behavior of the instruction depends on the value of CR4.PCIDE:
— If CR4.PCIDE = 0, the instruction invalidates all TLB entries associated with PCID 000H except those for
global pages. It also invalidates all entries in all paging-structure caches associated with PCID 000H.
— If CR4.PCIDE = 1 and bit 63 of the instruction’s source operand is 0, the instruction invalidates all TLB
entries associated with the PCID specified in bits 11:0 of the instruction’s source operand except those for
global pages. It also invalidates all entries in all paging-structure caches associated with that PCID. It is not
required to invalidate entries in the TLBs and paging-structure caches that are associated with other PCIDs.
— If CR4.PCIDE = 1 and bit 63 of the instruction’s source operand is 1, the instruction is not required to
invalidate any TLB entries or entries in paging-structure caches.
•
MOV to CR4. The behavior of the instruction depends on the bits being modified:
— The instruction invalidates all TLB entries (including global entries) and all entries in all paging-structure
caches (for all PCIDs) if (1) it changes the value of CR4.PGE;2 or (2) it changes the value of the CR4.PCIDE
from 1 to 0.
— The instruction invalidates all TLB entries and all entries in all paging-structure caches for the current PCID
if (1) it changes the value of CR4.PAE; or (2) it changes the value of CR4.SMEP from 0 to 1.
•
Task switch. If a task switch changes the value of CR3, it invalidates all TLB entries associated with PCID 000H
except those for global pages. It also invalidates all entries in all paging-structure caches for associated with
PCID 000H.3
•
VMX transitions. See Section 4.11.1.
The processor is always free to invalidate additional entries in the TLBs and paging-structure caches. The following
are some examples:
•
INVLPG may invalidate TLB entries for pages other than the one corresponding to its linear-address operand. It
may invalidate TLB entries and paging-structure-cache entries associated with PCIDs other than the current
PCID.
1. If the paging structures map the linear address using a page larger than 4 KBytes and there are multiple TLB entries for that page
(see Section 4.10.2.3), the instruction invalidates all of them.
2. If CR4.PGE is changing from 0 to 1, there were no global TLB entries before the execution; if CR4.PGE is changing from 1 to 0, there
will be no global TLB entries after the execution.
3. Task switches do not occur in IA-32e mode and thus cannot occur with IA-32e paging. Since CR4.PCIDE can be set only with IA-32e
paging, task switches occur only with CR4.PCIDE = 0.
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•
INVPCID may invalidate TLB entries for pages other than the one corresponding to the specified linear address.
It may invalidate TLB entries and paging-structure-cache entries associated with PCIDs other than the specified
PCID.
•
MOV to CR0 may invalidate TLB entries even if CR0.PG is not changing. For example, this may occur if either
CR0.CD or CR0.NW is modified.
•
MOV to CR3 may invalidate TLB entries for global pages. If CR4.PCIDE = 1 and bit 63 of the instruction’s source
operand is 0, it may invalidate TLB entries and entries in the paging-structure caches associated with PCIDs
other than the current PCID. It may invalidate entries if CR4.PCIDE = 1 and bit 63 of the instruction’s source
operand is 1.
•
•
MOV to CR4 may invalidate TLB entries when changing CR4.PSE or when changing CR4.SMEP from 1 to 0.
On a processor supporting Hyper-Threading Technology, invalidations performed on one logical processor may
invalidate entries in the TLBs and paging-structure caches used by other logical processors.
(Other instructions and operations may invalidate entries in the TLBs and the paging-structure caches, but the
instructions identified above are recommended.)
In addition to the instructions identified above, page faults invalidate entries in the TLBs and paging-structure
caches. In particular, a page-fault exception resulting from an attempt to use a linear address will invalidate any
TLB entries that are for a page number corresponding to that linear address and that are associated with the
current PCID. it also invalidates all entries in the paging-structure caches that would be used for that linear address
and that are associated with the current PCID.1 These invalidations ensure that the page-fault exception will not
recur (if the faulting instruction is re-executed) if it would not be caused by the contents of the paging structures
in memory (and if, therefore, it resulted from cached entries that were not invalidated after the paging structures
were modified in memory).
As noted in Section 4.10.2, some processors may choose to cache multiple smaller-page TLB entries for a translation specified by the paging structures to use a page larger than 4 KBytes. There is no way for software to be aware
that multiple translations for smaller pages have been used for a large page. The INVLPG instruction and page
faults provide the same assurances that they provide when a single TLB entry is used: they invalidate all TLB
entries corresponding to the translation specified by the paging structures.
4.10.4.2
Recommended Invalidation
The following items provide some recommendations regarding when software should perform invalidations:
•
If software modifies a paging-structure entry that identifies the final page frame for a page number (either a
PTE or a paging-structure entry in which the PS flag is 1), it should execute INVLPG for any linear address with
a page number whose translation uses that PTE.2
(If the paging-structure entry may be used in the translation of different page numbers — see Section 4.10.3.3
— software should execute INVLPG for linear addresses with each of those page numbers; alternatively, it could
use MOV to CR3 or MOV to CR4.)
•
If software modifies a paging-structure entry that references another paging structure, it may use one of the
following approaches depending upon the types and number of translations controlled by the modified entry:
— Execute INVLPG for linear addresses with each of the page numbers with translations that would use the
entry. However, if no page numbers that would use the entry have translations (e.g., because the P flags are
0 in all entries in the paging structure referenced by the modified entry), it remains necessary to execute
INVLPG at least once.
— Execute MOV to CR3 if the modified entry controls no global pages.
— Execute MOV to CR4 to modify CR4.PGE.
•
If CR4.PCIDE = 1 and software modifies a paging-structure entry that does not map a page or in which the G
flag (bit 8) is 0, additional steps are required if the entry may be used for PCIDs other than the current one. Any
one of the following suffices:
1. Unlike INVLPG, page faults need not invalidate all entries in the paging-structure caches, only those that would be used to translate
the faulting linear address.
2. One execution of INVLPG is sufficient even for a page with size greater than 4 KBytes.
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— Execute MOV to CR4 to modify CR4.PGE, either immediately or before again using any of the affected
PCIDs. For example, software could use different (previously unused) PCIDs for the processes that used the
affected PCIDs.
— For each affected PCID, execute MOV to CR3 to make that PCID current (and to load the address of the
appropriate PML4 table). If the modified entry controls no global pages and bit 63 of the source operand to
MOV to CR3 was 0, no further steps are required. Otherwise, execute INVLPG for linear addresses with each
of the page numbers with translations that would use the entry; if no page numbers that would use the
entry have translations, execute INVLPG at least once.
•
If software using PAE paging modifies a PDPTE, it should reload CR3 with the register’s current value to ensure
that the modified PDPTE is loaded into the corresponding PDPTE register (see Section 4.4.1).
•
If the nature of the paging structures is such that a single entry may be used for multiple purposes (see Section
4.10.3.3), software should perform invalidations for all of these purposes. For example, if a single entry might
serve as both a PDE and PTE, it may be necessary to execute INVLPG with two (or more) linear addresses, one
that uses the entry as a PDE and one that uses it as a PTE. (Alternatively, software could use MOV to CR3 or
MOV to CR4.)
•
As noted in Section 4.10.2, the TLBs may subsequently contain multiple translations for the address range if
software modifies the paging structures so that the page size used for a 4-KByte range of linear addresses
changes. A reference to a linear address in the address range may use any of these translations.
Software wishing to prevent this uncertainty should not write to a paging-structure entry in a way that would
change, for any linear address, both the page size and either the page frame, access rights, or other attributes.
It can instead use the following algorithm: first clear the P flag in the relevant paging-structure entry (e.g.,
PDE); then invalidate any translations for the affected linear addresses (see above); and then modify the
relevant paging-structure entry to set the P flag and establish modified translation(s) for the new page size.
•
Software should clear bit 63 of the source operand to a MOV to CR3 instruction that establishes a PCID that had
been used earlier for a different linear-address space (e.g., with a different value in bits 51:12 of CR3). This
ensures invalidation of any information that may have been cached for the previous linear-address space.
This assumes that both linear-address spaces use the same global pages and that it is thus not necessary to
invalidate any global TLB entries. If that is not the case, software should invalidate those entries by executing
MOV to CR4 to modify CR4.PGE.
4.10.4.3
Optional Invalidation
The following items describe cases in which software may choose not to invalidate and the potential consequences
of that choice:
•
If a paging-structure entry is modified to change the P flag from 0 to 1, no invalidation is necessary. This is
because no TLB entry or paging-structure cache entry is created with information from a paging-structure
entry in which the P flag is 0.1
•
If a paging-structure entry is modified to change the accessed flag from 0 to 1, no invalidation is necessary
(assuming that an invalidation was performed the last time the accessed flag was changed from 1 to 0). This is
because no TLB entry or paging-structure cache entry is created with information from a paging-structure
entry in which the accessed flag is 0.
•
If a paging-structure entry is modified to change the R/W flag from 0 to 1, failure to perform an invalidation
may result in a “spurious” page-fault exception (e.g., in response to an attempted write access) but no other
adverse behavior. Such an exception will occur at most once for each affected linear address (see Section
4.10.4.1).
•
If CR4.SMEP = 0 and a paging-structure entry is modified to change the U/S flag from 0 to 1, failure to perform
an invalidation may result in a “spurious” page-fault exception (e.g., in response to an attempted user-mode
access) but no other adverse behavior. Such an exception will occur at most once for each affected linear
address (see Section 4.10.4.1).
•
If a paging-structure entry is modified to change the XD flag from 1 to 0, failure to perform an invalidation may
result in a “spurious” page-fault exception (e.g., in response to an attempted instruction fetch) but no other
1. If it is also the case that no invalidation was performed the last time the P flag was changed from 1 to 0, the processor may use a
TLB entry or paging-structure cache entry that was created when the P flag had earlier been 1.
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adverse behavior. Such an exception will occur at most once for each affected linear address (see Section
4.10.4.1).
•
If a paging-structure entry is modified to change the accessed flag from 1 to 0, failure to perform an invalidation may result in the processor not setting that bit in response to a subsequent access to a linear address
whose translation uses the entry. Software cannot interpret the bit being clear as an indication that such an
access has not occurred.
•
If software modifies a paging-structure entry that identifies the final physical address for a linear address
(either a PTE or a paging-structure entry in which the PS flag is 1) to change the dirty flag from 1 to 0, failure
to perform an invalidation may result in the processor not setting that bit in response to a subsequent write to
a linear address whose translation uses the entry. Software cannot interpret the bit being clear as an indication
that such a write has not occurred.
•
The read of a paging-structure entry in translating an address being used to fetch an instruction may appear to
execute before an earlier write to that paging-structure entry if there is no serializing instruction between the
write and the instruction fetch. Note that the invalidating instructions identified in Section 4.10.4.1 are all
serializing instructions.
•
Section 4.10.3.3 describes situations in which a single paging-structure entry may contain information cached
in multiple entries in the paging-structure caches. Because all entries in these caches are invalidated by any
execution of INVLPG, it is not necessary to follow the modification of such a paging-structure entry by
executing INVLPG multiple times solely for the purpose of invalidating these multiple cached entries. (It may be
necessary to do so to invalidate multiple TLB entries.)
4.10.4.4
Delayed Invalidation
Required invalidations may be delayed under some circumstances. Software developers should understand that,
between the modification of a paging-structure entry and execution of the invalidation instruction recommended in
Section 4.10.4.2, the processor may use translations based on either the old value or the new value of the pagingstructure entry. The following items describe some of the potential consequences of delayed invalidation:
•
If a paging-structure entry is modified to change from 1 to 0 the P flag from 1 to 0, an access to a linear address
whose translation is controlled by this entry may or may not cause a page-fault exception.
•
If a paging-structure entry is modified to change the R/W flag from 0 to 1, write accesses to linear addresses
whose translation is controlled by this entry may or may not cause a page-fault exception.
•
If a paging-structure entry is modified to change the U/S flag from 0 to 1, user-mode accesses to linear
addresses whose translation is controlled by this entry may or may not cause a page-fault exception.
•
If a paging-structure entry is modified to change the XD flag from 1 to 0, instruction fetches from linear
addresses whose translation is controlled by this entry may or may not cause a page-fault exception.
As noted in Section 8.1.1, an x87 instruction or an SSE instruction that accesses data larger than a quadword may
be implemented using multiple memory accesses. If such an instruction stores to memory and invalidation has
been delayed, some of the accesses may complete (writing to memory) while another causes a page-fault exception.1 In this case, the effects of the completed accesses may be visible to software even though the overall instruction caused a fault.
In some cases, the consequences of delayed invalidation may not affect software adversely. For example, when
freeing a portion of the linear-address space (by marking paging-structure entries “not present”), invalidation
using INVLPG may be delayed if software does not re-allocate that portion of the linear-address space or the
memory that had been associated with it. However, because of speculative execution (or errant software), there
may be accesses to the freed portion of the linear-address space before the invalidations occur. In this case, the
following can happen:
•
Reads can occur to the freed portion of the linear-address space. Therefore, invalidation should not be delayed
for an address range that has read side effects.
•
The processor may retain entries in the TLBs and paging-structure caches for an extended period of time.
Software should not assume that the processor will not use entries associated with a linear address simply
because time has passed.
1. If the accesses are to different pages, this may occur even if invalidation has not been delayed.
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•
As noted in Section 4.10.3.1, the processor may create an entry in a paging-structure cache even if there are
no translations for any linear address that might use that entry. Thus, if software has marked “not present” all
entries in page table, the processor may subsequently create a PDE-cache entry for the PDE that references
that page table (assuming that the PDE itself is marked “present”).
•
If software attempts to write to the freed portion of the linear-address space, the processor might not generate
a page fault. (Such an attempt would likely be the result of a software error.) For that reason, the page frames
previously associated with the freed portion of the linear-address space should not be reallocated for another
purpose until the appropriate invalidations have been performed.
4.10.5
Propagation of Paging-Structure Changes to Multiple Processors
As noted in Section 4.10.4, software that modifies a paging-structure entry may need to invalidate entries in the
TLBs and paging-structure caches that were derived from the modified entry before it was modified. In a system
containing more than one logical processor, software must account for the fact that there may be entries in the
TLBs and paging-structure caches of logical processors other than the one used to modify the paging-structure
entry. The process of propagating the changes to a paging-structure entry is commonly referred to as “TLB shootdown.”
TLB shootdown can be done using memory-based semaphores and/or interprocessor interrupts (IPI). The
following items describe a simple but inefficient example of a TLB shootdown algorithm for processors supporting
the Intel-64 and IA-32 architectures:
1. Begin barrier: Stop all but one logical processor; that is, cause all but one to execute the HLT instruction or to
enter a spin loop.
2. Allow the active logical processor to change the necessary paging-structure entries.
3. Allow all logical processors to perform invalidations appropriate to the modifications to the paging-structure
entries.
4. Allow all logical processors to resume normal operation.
Alternative, performance-optimized, TLB shootdown algorithms may be developed; however, software developers
must take care to ensure that the following conditions are met:
•
All logical processors that are using the paging structures that are being modified must participate and perform
appropriate invalidations after the modifications are made.
•
If the modifications to the paging-structure entries are made before the barrier or if there is no barrier, the
operating system must ensure one of the following: (1) that the affected linear-address range is not used
between the time of modification and the time of invalidation; or (2) that it is prepared to deal with the consequences of the affected linear-address range being used during that period. For example, if the operating
system does not allow pages being freed to be reallocated for another purpose until after the required invalidations, writes to those pages by errant software will not unexpectedly modify memory that is in use.
•
Software must be prepared to deal with reads, instruction fetches, and prefetch requests to the affected linearaddress range that are a result of speculative execution that would never actually occur in the executed code
path.
When multiple logical processors are using the same linear-address space at the same time, they must coordinate
before any request to modify the paging-structure entries that control that linear-address space. In these cases,
the barrier in the TLB shootdown routine may not be required. For example, when freeing a range of linear
addresses, some other mechanism can assure no logical processor is using that range before the request to free it
is made. In this case, a logical processor freeing the range can clear the P flags in the PTEs associated with the
range, free the physical page frames associated with the range, and then signal the other logical processors using
that linear-address space to perform the necessary invalidations. All the affected logical processors must complete
their invalidations before the linear-address range and the physical page frames previously associated with that
range can be reallocated.
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4.11
INTERACTIONS WITH VIRTUAL-MACHINE EXTENSIONS (VMX)
The architecture for virtual-machine extensions (VMX) includes features that interact with paging. Section 4.11.1
discusses ways in which VMX-specific control transfers, called VMX transitions specially affect paging. Section
4.11.2 gives an overview of VMX features specifically designed to support address translation.
4.11.1
VMX Transitions
The VMX architecture defines two control transfers called VM entries and VM exits; collectively, these are called
VMX transitions. VM entries and VM exits are described in detail in Chapter 26 and Chapter 27, respectively, in
the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3C. The following items identify
paging-related details:
•
VMX transitions modify the CR0 and CR4 registers and the IA32_EFER MSR concurrently. For this reason, they
allow transitions between paging modes that would not otherwise be possible:
— VM entries allow transitions from IA-32e paging directly to either 32-bit paging or PAE paging.
— VM exits allow transitions from either 32-bit paging or PAE paging directly to IA-32e paging.
•
VMX transitions that result in PAE paging load the PDPTE registers (see Section 4.4.1) as follows:
— VM entries load the PDPTE registers either from the physical address being loaded into CR3 or from the
virtual-machine control structure (VMCS); see Section 26.3.2.4.
— VM exits load the PDPTE registers from the physical address being loaded into CR3; see Section 27.5.4.
•
VMX transitions invalidate the TLBs and paging-structure caches based on certain control settings. See Section
26.3.2.5 and Section 27.5.5 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume
3C.
4.11.2
VMX Support for Address Translation
Chapter 28, “VMX Support for Address Translation,” in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 3C describe two features of the virtual-machine extensions (VMX) that interact directly with
paging. These are virtual-processor identifiers (VPIDs) and the extended page table mechanism (EPT).
VPIDs provide a way for software to identify to the processor the address spaces for different “virtual processors.”
The processor may use this identification to maintain concurrently information for multiple address spaces in its
TLBs and paging-structure caches, even when non-zero PCIDs are not being used. See Section 28.1 for details.
When EPT is in use, the addresses in the paging-structures are not used as physical addresses to access memory
and memory-mapped I/O. Instead, they are treated as guest-physical addresses and are translated through a set
of EPT paging structures to produce physical addresses. EPT can also specify its own access rights and memory
typing; these are used on conjunction with those specified in this chapter. See Section 28.2 for more information.
Both VPIDs and EPT may change the way that a processor maintains information in TLBs and paging structure
caches and the ways in which software can manage that information. Some of the behaviors documented in Section
4.10 may change. See Section 28.3 for details.
4.12
USING PAGING FOR VIRTUAL MEMORY
With paging, portions of the linear-address space need not be mapped to the physical-address space; data for the
unmapped addresses can be stored externally (e.g., on disk). This method of mapping the linear-address space is
referred to as virtual memory or demand-paged virtual memory.
Paging divides the linear address space into fixed-size pages that can be mapped into the physical-address space
and/or external storage. When a program (or task) references a linear address, the processor uses paging to translate the linear address into a corresponding physical address if such an address is defined.
If the page containing the linear address is not currently mapped into the physical-address space, the processor
generates a page-fault exception as described in Section 4.7. The handler for page-fault exceptions typically
4-44 Vol. 3A
PAGING
directs the operating system or executive to load data for the unmapped page from external storage into physical
memory (perhaps writing a different page from physical memory out to external storage in the process) and to
map it using paging (by updating the paging structures). When the page has been loaded into physical memory, a
return from the exception handler causes the instruction that generated the exception to be restarted.
Paging differs from segmentation through its use of fixed-size pages. Unlike segments, which usually are the same
size as the code or data structures they hold, pages have a fixed size. If segmentation is the only form of address
translation used, a data structure present in physical memory will have all of its parts in memory. If paging is used,
a data structure can be partly in memory and partly in disk storage.
4.13
MAPPING SEGMENTS TO PAGES
The segmentation and paging mechanisms provide in the support a wide variety of approaches to memory
management. When segmentation and paging are combined, segments can be mapped to pages in several ways.
To implement a flat (unsegmented) addressing environment, for example, all the code, data, and stack modules
can be mapped to one or more large segments (up to 4-GBytes) that share same range of linear addresses (see
Figure 3-2 in Section 3.2.2). Here, segments are essentially invisible to applications and the operating-system or
executive. If paging is used, the paging mechanism can map a single linear-address space (contained in a single
segment) into virtual memory. Alternatively, each program (or task) can have its own large linear-address space
(contained in its own segment), which is mapped into virtual memory through its own paging structures.
Segments can be smaller than the size of a page. If one of these segments is placed in a page which is not shared
with another segment, the extra memory is wasted. For example, a small data structure, such as a 1-Byte semaphore, occupies 4 KBytes if it is placed in a page by itself. If many semaphores are used, it is more efficient to pack
them into a single page.
The Intel-64 and IA-32 architectures do not enforce correspondence between the boundaries of pages and
segments. A page can contain the end of one segment and the beginning of another. Similarly, a segment can
contain the end of one page and the beginning of another.
Memory-management software may be simpler and more efficient if it enforces some alignment between page and
segment boundaries. For example, if a segment which can fit in one page is placed in two pages, there may be
twice as much paging overhead to support access to that segment.
One approach to combining paging and segmentation that simplifies memory-management software is to give
each segment its own page table, as shown in Figure 4-13. This convention gives the segment a single entry in the
page directory, and this entry provides the access control information for paging the entire segment.
Page Frames
LDT
Page Directory
Page Tables
PTE
PTE
PTE
Seg. Descript.
Seg. Descript.
PDE
PDE
PTE
PTE
Figure 4-13. Memory Management Convention That Assigns a Page Table
to Each Segment
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PAGING
4-46 Vol. 3A
CHAPTER 5
PROTECTION
In protected mode, the Intel 64 and IA-32 architectures provide a protection mechanism that operates at both the
segment level and the page level. This protection mechanism provides the ability to limit access to certain
segments or pages based on privilege levels (four privilege levels for segments and two privilege levels for pages).
For example, critical operating-system code and data can be protected by placing them in more privileged
segments than those that contain applications code. The processor’s protection mechanism will then prevent application code from accessing the operating-system code and data in any but a controlled, defined manner.
Segment and page protection can be used at all stages of software development to assist in localizing and detecting
design problems and bugs. It can also be incorporated into end-products to offer added robustness to operating
systems, utilities software, and applications software.
When the protection mechanism is used, each memory reference is checked to verify that it satisfies various
protection checks. All checks are made before the memory cycle is started; any violation results in an exception.
Because checks are performed in parallel with address translation, there is no performance penalty. The protection
checks that are performed fall into the following categories:
•
•
•
•
•
•
Limit checks.
Type checks.
Privilege level checks.
Restriction of addressable domain.
Restriction of procedure entry-points.
Restriction of instruction set.
All protection violation results in an exception being generated. See Chapter 6, “Interrupt and Exception Handling,”
for an explanation of the exception mechanism. This chapter describes the protection mechanism and the violations which lead to exceptions.
The following sections describe the protection mechanism available in protected mode. See Chapter 20, “8086
Emulation,” for information on protection in real-address and virtual-8086 mode.
5.1
ENABLING AND DISABLING SEGMENT AND PAGE PROTECTION
Setting the PE flag in register CR0 causes the processor to switch to protected mode, which in turn enables the
segment-protection mechanism. Once in protected mode, there is no control bit for turning the protection mechanism on or off. The part of the segment-protection mechanism that is based on privilege levels can essentially be
disabled while still in protected mode by assigning a privilege level of 0 (most privileged) to all segment selectors
and segment descriptors. This action disables the privilege level protection barriers between segments, but other
protection checks such as limit checking and type checking are still carried out.
Page-level protection is automatically enabled when paging is enabled (by setting the PG flag in register CR0). Here
again there is no mode bit for turning off page-level protection once paging is enabled. However, page-level protection can be disabled by performing the following operations:
•
•
Clear the WP flag in control register CR0.
Set the read/write (R/W) and user/supervisor (U/S) flags for each page-directory and page-table entry.
This action makes each page a writable, user page, which in effect disables page-level protection.
Vol. 3A 5-1
PROTECTION
5.2
FIELDS AND FLAGS USED FOR SEGMENT-LEVEL AND
PAGE-LEVEL PROTECTION
The processor’s protection mechanism uses the following fields and flags in the system data structures to control
access to segments and pages:
•
Descriptor type (S) flag — (Bit 12 in the second doubleword of a segment descriptor.) Determines if the
segment descriptor is for a system segment or a code or data segment.
•
Type field — (Bits 8 through 11 in the second doubleword of a segment descriptor.) Determines the type of
code, data, or system segment.
•
Limit field — (Bits 0 through 15 of the first doubleword and bits 16 through 19 of the second doubleword of a
segment descriptor.) Determines the size of the segment, along with the G flag and E flag (for data segments).
•
G flag — (Bit 23 in the second doubleword of a segment descriptor.) Determines the size of the segment, along
with the limit field and E flag (for data segments).
•
E flag — (Bit 10 in the second doubleword of a data-segment descriptor.) Determines the size of the segment,
along with the limit field and G flag.
•
Descriptor privilege level (DPL) field — (Bits 13 and 14 in the second doubleword of a segment descriptor.)
Determines the privilege level of the segment.
•
Requested privilege level (RPL) field — (Bits 0 and 1 of any segment selector.) Specifies the requested
privilege level of a segment selector.
•
Current privilege level (CPL) field — (Bits 0 and 1 of the CS segment register.) Indicates the privilege level
of the currently executing program or procedure. The term current privilege level (CPL) refers to the setting of
this field.
•
User/supervisor (U/S) flag — (Bit 2 of paging-structure entries.) Determines the type of page: user or
supervisor.
•
Read/write (R/W) flag — (Bit 1 of paging-structure entries.) Determines the type of access allowed to a
page: read-only or read/write.
•
Execute-disable (XD) flag — (Bit 63 of certain paging-structure entries.) Determines the type of access
allowed to a page: executable or not-executable.
Figure 5-1 shows the location of the various fields and flags in the data, code, and system- segment descriptors;
Figure 3-6 shows the location of the RPL (or CPL) field in a segment selector (or the CS register); and Chapter 4
identifies the locations of the U/S, R/W, and XD flags in the paging-structure entries.
5-2 Vol. 3A
PROTECTION
Data-Segment Descriptor
31
Base 31:24
24 23 22 21 20 19
16 15 14 13 12 11
A
G B 0 V
L
D
P
L
Limit
19:16
31
P
0
8 7
Type
Base 23:16
4
1 0 E W A
16 15
0
Base Address 15:00
Segment Limit 15:00
0
Code-Segment Descriptor
31
Base 31:24
24 23 22 21 20 19
16 15 14 13 12 11
A
G D 0 V
L
D
P
L
Limit
19:16
31
P
0
8 7
Type
Base 23:16
4
1 1 C R A
16 15
0
Base Address 15:00
Segment Limit 15:00
0
System-Segment Descriptor
31
24 23 22 21 20 19
Base 31:24
G
0
31
16 15 14 13 12 11
Limit
19:16
P
D
P
L
0
0
8 7
Type
Base 23:16
16 15
Base Address 15:00
A
AVL
B
C
D
DPL
Accessed
Available to Sys. Programmer’s
Big
Conforming
Default
Descriptor Privilege Level
4
0
Segment Limit 15:00
E
G
R
LIMIT
W
P
0
Expansion Direction
Granularity
Readable
Segment Limit
Writable
Present
Reserved
Figure 5-1. Descriptor Fields Used for Protection
Many different styles of protection schemes can be implemented with these fields and flags. When the operating
system creates a descriptor, it places values in these fields and flags in keeping with the particular protection style
chosen for an operating system or executive. Application program do not generally access or modify these fields
and flags.
The following sections describe how the processor uses these fields and flags to perform the various categories of
checks described in the introduction to this chapter.
5.2.1
Code Segment Descriptor in 64-bit Mode
Code segments continue to exist in 64-bit mode even though, for address calculations, the segment base is treated
as zero. Some code-segment (CS) descriptor content (the base address and limit fields) is ignored; the remaining
fields function normally (except for the readable bit in the type field).
Code segment descriptors and selectors are needed in IA-32e mode to establish the processor’s operating mode
and execution privilege-level. The usage is as follows:
Vol. 3A 5-3
PROTECTION
•
IA-32e mode uses a previously unused bit in the CS descriptor. Bit 53 is defined as the 64-bit (L) flag and is
used to select between 64-bit mode and compatibility mode when IA-32e mode is active (IA32_EFER.LMA = 1).
See Figure 5-2.
— If CS.L = 0 and IA-32e mode is active, the processor is running in compatibility mode. In this case, CS.D
selects the default size for data and addresses. If CS.D = 0, the default data and address size is 16 bits. If
CS.D = 1, the default data and address size is 32 bits.
— If CS.L = 1 and IA-32e mode is active, the only valid setting is CS.D = 0. This setting indicates a default
operand size of 32 bits and a default address size of 64 bits. The CS.L = 1 and CS.D = 1 bit combination is
reserved for future use and a #GP fault will be generated on an attempt to use a code segment with these
bits set in IA-32e mode.
•
In IA-32e mode, the CS descriptor’s DPL is used for execution privilege checks (as in legacy 32-bit mode).
Code-Segment Descriptor
31
24 23 22 21 20 19
16 15 14 13 12 11
A
G D L V
L
D
P
L
P
8 7
0
Type
4
1 1 C R A
0
31
0
A
AVL
C
D
DPL
L
Accessed
Available to Sys. Programmer’s
Conforming
Default
Descriptor Privilege Level
64-Bit Flag
G
R
P
Granularity
Readable
Present
Figure 5-2. Descriptor Fields with Flags used in IA-32e Mode
5.3
LIMIT CHECKING
The limit field of a segment descriptor prevents programs or procedures from addressing memory locations outside
the segment. The effective value of the limit depends on the setting of the G (granularity) flag (see Figure 5-1). For
data segments, the limit also depends on the E (expansion direction) flag and the B (default stack pointer size
and/or upper bound) flag. The E flag is one of the bits in the type field when the segment descriptor is for a datasegment type.
When the G flag is clear (byte granularity), the effective limit is the value of the 20-bit limit field in the segment
descriptor. Here, the limit ranges from 0 to FFFFFH (1 MByte). When the G flag is set (4-KByte page granularity),
the processor scales the value in the limit field by a factor of 212 (4 KBytes). In this case, the effective limit ranges
from FFFH (4 KBytes) to FFFFFFFFH (4 GBytes). Note that when scaling is used (G flag is set), the lower 12 bits of
a segment offset (address) are not checked against the limit; for example, note that if the segment limit is 0,
offsets 0 through FFFH are still valid.
For all types of segments except expand-down data segments, the effective limit is the last address that is allowed
to be accessed in the segment, which is one less than the size, in bytes, of the segment. The processor causes a
general-protection exception (or, if the segment is SS, a stack-fault exception) any time an attempt is made to
access the following addresses in a segment:
•
•
•
•
A byte at an offset greater than the effective limit
A word at an offset greater than the (effective-limit – 1)
A doubleword at an offset greater than the (effective-limit – 3)
A quadword at an offset greater than the (effective-limit – 7)
5-4 Vol. 3A
PROTECTION
•
A double quadword at an offset greater than the (effective limit – 15)
When the effective limit is FFFFFFFFH (4 GBytes), these accesses may or may not cause the indicated exceptions.
Behavior is implementation-specific and may vary from one execution to another.
For expand-down data segments, the segment limit has the same function but is interpreted differently. Here, the
effective limit specifies the last address that is not allowed to be accessed within the segment; the range of valid
offsets is from (effective-limit + 1) to FFFFFFFFH if the B flag is set and from (effective-limit + 1) to FFFFH if the B
flag is clear. An expand-down segment has maximum size when the segment limit is 0.
Limit checking catches programming errors such as runaway code, runaway subscripts, and invalid pointer calculations. These errors are detected when they occur, so identification of the cause is easier. Without limit checking,
these errors could overwrite code or data in another segment.
In addition to checking segment limits, the processor also checks descriptor table limits. The GDTR and IDTR registers contain 16-bit limit values that the processor uses to prevent programs from selecting a segment descriptors
outside the respective descriptor tables. The LDTR and task registers contain 32-bit segment limit value (read from
the segment descriptors for the current LDT and TSS, respectively). The processor uses these segment limits to
prevent accesses beyond the bounds of the current LDT and TSS. See Section 3.5.1, “Segment Descriptor Tables,”
for more information on the GDT and LDT limit fields; see Section 6.10, “Interrupt Descriptor Table (IDT),” for more
information on the IDT limit field; and see Section 7.2.4, “Task Register,” for more information on the TSS segment
limit field.
5.3.1
Limit Checking in 64-bit Mode
In 64-bit mode, the processor does not perform runtime limit checking on code or data segments. However, the
processor does check descriptor-table limits.
5.4
TYPE CHECKING
Segment descriptors contain type information in two places:
•
•
The S (descriptor type) flag.
The type field.
The processor uses this information to detect programming errors that result in an attempt to use a segment or
gate in an incorrect or unintended manner.
The S flag indicates whether a descriptor is a system type or a code or data type. The type field provides 4 additional bits for use in defining various types of code, data, and system descriptors. Table 3-1 shows the encoding of
the type field for code and data descriptors; Table 3-2 shows the encoding of the field for system descriptors.
The processor examines type information at various times while operating on segment selectors and segment
descriptors. The following list gives examples of typical operations where type checking is performed (this list is not
exhaustive):
•
When a segment selector is loaded into a segment register — Certain segment registers can contain only
certain descriptor types, for example:
— The CS register only can be loaded with a selector for a code segment.
— Segment selectors for code segments that are not readable or for system segments cannot be loaded into
data-segment registers (DS, ES, FS, and GS).
— Only segment selectors of writable data segments can be loaded into the SS register.
•
When a segment selector is loaded into the LDTR or task register — For example:
— The LDTR can only be loaded with a selector for an LDT.
— The task register can only be loaded with a segment selector for a TSS.
•
When instructions access segments whose descriptors are already loaded into segment registers —
Certain segments can be used by instructions only in certain predefined ways, for example:
— No instruction may write into an executable segment.
Vol. 3A 5-5
PROTECTION
— No instruction may write into a data segment if it is not writable.
— No instruction may read an executable segment unless the readable flag is set.
•
When an instruction operand contains a segment selector — Certain instructions can access segments
or gates of only a particular type, for example:
— A far CALL or far JMP instruction can only access a segment descriptor for a conforming code segment,
nonconforming code segment, call gate, task gate, or TSS.
— The LLDT instruction must reference a segment descriptor for an LDT.
— The LTR instruction must reference a segment descriptor for a TSS.
— The LAR instruction must reference a segment or gate descriptor for an LDT, TSS, call gate, task gate, code
segment, or data segment.
— The LSL instruction must reference a segment descriptor for a LDT, TSS, code segment, or data segment.
— IDT entries must be interrupt, trap, or task gates.
•
During certain internal operations — For example:
— On a far call or far jump (executed with a far CALL or far JMP instruction), the processor determines the
type of control transfer to be carried out (call or jump to another code segment, a call or jump through a
gate, or a task switch) by checking the type field in the segment (or gate) descriptor pointed to by the
segment (or gate) selector given as an operand in the CALL or JMP instruction. If the descriptor type is for
a code segment or call gate, a call or jump to another code segment is indicated; if the descriptor type is for
a TSS or task gate, a task switch is indicated.
— On a call or jump through a call gate (or on an interrupt- or exception-handler call through a trap or
interrupt gate), the processor automatically checks that the segment descriptor being pointed to by the
gate is for a code segment.
— On a call or jump to a new task through a task gate (or on an interrupt- or exception-handler call to a new
task through a task gate), the processor automatically checks that the segment descriptor being pointed to
by the task gate is for a TSS.
— On a call or jump to a new task by a direct reference to a TSS, the processor automatically checks that the
segment descriptor being pointed to by the CALL or JMP instruction is for a TSS.
— On return from a nested task (initiated by an IRET instruction), the processor checks that the previous task
link field in the current TSS points to a TSS.
5.4.1
Null Segment Selector Checking
Attempting to load a null segment selector (see Section 3.4.2, “Segment Selectors”) into the CS or SS segment
register generates a general-protection exception (#GP). A null segment selector can be loaded into the DS, ES,
FS, or GS register, but any attempt to access a segment through one of these registers when it is loaded with a null
segment selector results in a #GP exception being generated. Loading unused data-segment registers with a null
segment selector is a useful method of detecting accesses to unused segment registers and/or preventing
unwanted accesses to data segments.
5.4.1.1
NULL Segment Checking in 64-bit Mode
In 64-bit mode, the processor does not perform runtime checking on NULL segment selectors. The processor does
not cause a #GP fault when an attempt is made to access memory where the referenced segment register has a
NULL segment selector.
5.5
PRIVILEGE LEVELS
The processor’s segment-protection mechanism recognizes 4 privilege levels, numbered from 0 to 3. The greater
numbers mean lesser privileges. Figure 5-3 shows how these levels of privilege can be interpreted as rings of
protection.
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PROTECTION
The center (reserved for the most privileged code, data, and stacks) is used for the segments containing the critical
software, usually the kernel of an operating system. Outer rings are used for less critical software. (Systems that
use only 2 of the 4 possible privilege levels should use levels 0 and 3.)
Protection Rings
Operating
System
Kernel
Level 0
Operating System
Services
Level 1
Level 2
Applications
Level 3
Figure 5-3. Protection Rings
The processor uses privilege levels to prevent a program or task operating at a lesser privilege level from accessing
a segment with a greater privilege, except under controlled situations. When the processor detects a privilege level
violation, it generates a general-protection exception (#GP).
To carry out privilege-level checks between code segments and data segments, the processor recognizes the
following three types of privilege levels:
•
Current privilege level (CPL) — The CPL is the privilege level of the currently executing program or task. It
is stored in bits 0 and 1 of the CS and SS segment registers. Normally, the CPL is equal to the privilege level of
the code segment from which instructions are being fetched. The processor changes the CPL when program
control is transferred to a code segment with a different privilege level. The CPL is treated slightly differently
when accessing conforming code segments. Conforming code segments can be accessed from any privilege
level that is equal to or numerically greater (less privileged) than the DPL of the conforming code segment.
Also, the CPL is not changed when the processor accesses a conforming code segment that has a different
privilege level than the CPL.
•
Descriptor privilege level (DPL) — The DPL is the privilege level of a segment or gate. It is stored in the DPL
field of the segment or gate descriptor for the segment or gate. When the currently executing code segment
attempts to access a segment or gate, the DPL of the segment or gate is compared to the CPL and RPL of the
segment or gate selector (as described later in this section). The DPL is interpreted differently, depending on
the type of segment or gate being accessed:
— Data segment — The DPL indicates the numerically highest privilege level that a program or task can have
to be allowed to access the segment. For example, if the DPL of a data segment is 1, only programs running
at a CPL of 0 or 1 can access the segment.
— Nonconforming code segment (without using a call gate) — The DPL indicates the privilege level that
a program or task must be at to access the segment. For example, if the DPL of a nonconforming code
segment is 0, only programs running at a CPL of 0 can access the segment.
— Call gate — The DPL indicates the numerically highest privilege level that the currently executing program
or task can be at and still be able to access the call gate. (This is the same access rule as for a data
segment.)
— Conforming code segment and nonconforming code segment accessed through a call gate — The
DPL indicates the numerically lowest privilege level that a program or task can have to be allowed to access
the segment. For example, if the DPL of a conforming code segment is 2, programs running at a CPL of 0 or
1 cannot access the segment.
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PROTECTION
— TSS — The DPL indicates the numerically highest privilege level that the currently executing program or
task can be at and still be able to access the TSS. (This is the same access rule as for a data segment.)
•
Requested privilege level (RPL) — The RPL is an override privilege level that is assigned to segment
selectors. It is stored in bits 0 and 1 of the segment selector. The processor checks the RPL along with the CPL
to determine if access to a segment is allowed. Even if the program or task requesting access to a segment has
sufficient privilege to access the segment, access is denied if the RPL is not of sufficient privilege level. That is,
if the RPL of a segment selector is numerically greater than the CPL, the RPL overrides the CPL, and vice versa.
The RPL can be used to insure that privileged code does not access a segment on behalf of an application
program unless the program itself has access privileges for that segment. See Section 5.10.4, “Checking Caller
Access Privileges (ARPL Instruction),” for a detailed description of the purpose and typical use of the RPL.
Privilege levels are checked when the segment selector of a segment descriptor is loaded into a segment register.
The checks used for data access differ from those used for transfers of program control among code segments;
therefore, the two kinds of accesses are considered separately in the following sections.
5.6
PRIVILEGE LEVEL CHECKING WHEN ACCESSING DATA SEGMENTS
To access operands in a data segment, the segment selector for the data segment must be loaded into the datasegment registers (DS, ES, FS, or GS) or into the stack-segment register (SS). (Segment registers can be loaded
with the MOV, POP, LDS, LES, LFS, LGS, and LSS instructions.) Before the processor loads a segment selector into
a segment register, it performs a privilege check (see Figure 5-4) by comparing the privilege levels of the currently
running program or task (the CPL), the RPL of the segment selector, and the DPL of the segment’s segment
descriptor. The processor loads the segment selector into the segment register if the DPL is numerically greater
than or equal to both the CPL and the RPL. Otherwise, a general-protection fault is generated and the segment
register is not loaded.
CS Register
CPL
Segment Selector
For Data Segment
RPL
Data-Segment Descriptor
Privilege
Check
DPL
Figure 5-4. Privilege Check for Data Access
Figure 5-5 shows four procedures (located in codes segments A, B, C, and D), each running at different privilege
levels and each attempting to access the same data segment.
1. The procedure in code segment A is able to access data segment E using segment selector E1, because the CPL
of code segment A and the RPL of segment selector E1 are equal to the DPL of data segment E.
2. The procedure in code segment B is able to access data segment E using segment selector E2, because the CPL
of code segment B and the RPL of segment selector E2 are both numerically lower than (more privileged) than
the DPL of data segment E. A code segment B procedure can also access data segment E using segment
selector E1.
3. The procedure in code segment C is not able to access data segment E using segment selector E3 (dotted line),
because the CPL of code segment C and the RPL of segment selector E3 are both numerically greater than (less
privileged) than the DPL of data segment E. Even if a code segment C procedure were to use segment selector
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E1 or E2, such that the RPL would be acceptable, it still could not access data segment E because its CPL is not
privileged enough.
4. The procedure in code segment D should be able to access data segment E because code segment D’s CPL is
numerically less than the DPL of data segment E. However, the RPL of segment selector E3 (which the code
segment D procedure is using to access data segment E) is numerically greater than the DPL of data segment
E, so access is not allowed. If the code segment D procedure were to use segment selector E1 or E2 to access
the data segment, access would be allowed.
3
2
1
0
Code
Segment C
CPL=3
Lowest Privilege
Segment Sel. E3
RPL=3
Code
Segment A
CPL=2
Segment Sel. E1
RPL=2
Code
Segment B
CPL=1
Segment Sel. E2
RPL=1
Data
Segment E
DPL=2
Code
Segment D
CPL=0
Highest Privilege
Figure 5-5. Examples of Accessing Data Segments From Various Privilege Levels
As demonstrated in the previous examples, the addressable domain of a program or task varies as its CPL changes.
When the CPL is 0, data segments at all privilege levels are accessible; when the CPL is 1, only data segments at
privilege levels 1 through 3 are accessible; when the CPL is 3, only data segments at privilege level 3 are accessible.
The RPL of a segment selector can always override the addressable domain of a program or task. When properly
used, RPLs can prevent problems caused by accidental (or intensional) use of segment selectors for privileged data
segments by less privileged programs or procedures.
It is important to note that the RPL of a segment selector for a data segment is under software control. For
example, an application program running at a CPL of 3 can set the RPL for a data- segment selector to 0. With the
RPL set to 0, only the CPL checks, not the RPL checks, will provide protection against deliberate, direct attempts to
violate privilege-level security for the data segment. To prevent these types of privilege-level-check violations, a
program or procedure can check access privileges whenever it receives a data-segment selector from another
procedure (see Section 5.10.4, “Checking Caller Access Privileges (ARPL Instruction)”).
5.6.1
Accessing Data in Code Segments
In some instances it may be desirable to access data structures that are contained in a code segment. The
following methods of accessing data in code segments are possible:
•
•
•
Load a data-segment register with a segment selector for a nonconforming, readable, code segment.
Load a data-segment register with a segment selector for a conforming, readable, code segment.
Use a code-segment override prefix (CS) to read a readable, code segment whose selector is already loaded in
the CS register.
The same rules for accessing data segments apply to method 1. Method 2 is always valid because the privilege
level of a conforming code segment is effectively the same as the CPL, regardless of its DPL. Method 3 is always
valid because the DPL of the code segment selected by the CS register is the same as the CPL.
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5.7
PRIVILEGE LEVEL CHECKING WHEN LOADING THE SS REGISTER
Privilege level checking also occurs when the SS register is loaded with the segment selector for a stack segment.
Here all privilege levels related to the stack segment must match the CPL; that is, the CPL, the RPL of the stacksegment selector, and the DPL of the stack-segment descriptor must be the same. If the RPL and DPL are not equal
to the CPL, a general-protection exception (#GP) is generated.
5.8
PRIVILEGE LEVEL CHECKING WHEN TRANSFERRING PROGRAM CONTROL
BETWEEN CODE SEGMENTS
To transfer program control from one code segment to another, the segment selector for the destination code
segment must be loaded into the code-segment register (CS). As part of this loading process, the processor examines the segment descriptor for the destination code segment and performs various limit, type, and privilege
checks. If these checks are successful, the CS register is loaded, program control is transferred to the new code
segment, and program execution begins at the instruction pointed to by the EIP register.
Program control transfers are carried out with the JMP, CALL, RET, SYSENTER, SYSEXIT, SYSCALL, SYSRET, INT n,
and IRET instructions, as well as by the exception and interrupt mechanisms. Exceptions, interrupts, and the IRET
instruction are special cases discussed in Chapter 6, “Interrupt and Exception Handling.” This chapter discusses
only the JMP, CALL, RET, SYSENTER, SYSEXIT, SYSCALL, and SYSRET instructions.
A JMP or CALL instruction can reference another code segment in any of four ways:
•
•
The target operand contains the segment selector for the target code segment.
•
•
The target operand points to a TSS, which contains the segment selector for the target code segment.
The target operand points to a call-gate descriptor, which contains the segment selector for the target code
segment.
The target operand points to a task gate, which points to a TSS, which in turn contains the segment selector for
the target code segment.
The following sections describe first two types of references. See Section 7.3, “Task Switching,” for information on
transferring program control through a task gate and/or TSS.
The SYSENTER and SYSEXIT instructions are special instructions for making fast calls to and returns from operating
system or executive procedures. These instructions are discussed in Section 5.8.7, “Performing Fast Calls to
System Procedures with the SYSENTER and SYSEXIT Instructions.”
The SYCALL and SYSRET instructions are special instructions for making fast calls to and returns from operating
system or executive procedures in 64-bit mode. These instructions are discussed in Section 5.8.8, “Fast System
Calls in 64-Bit Mode.”
5.8.1
Direct Calls or Jumps to Code Segments
The near forms of the JMP, CALL, and RET instructions transfer program control within the current code segment,
so privilege-level checks are not performed. The far forms of the JMP, CALL, and RET instructions transfer control
to other code segments, so the processor does perform privilege-level checks.
When transferring program control to another code segment without going through a call gate, the processor
examines four kinds of privilege level and type information (see Figure 5-6):
•
The CPL. (Here, the CPL is the privilege level of the calling code segment; that is, the code segment that
contains the procedure that is making the call or jump.)
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CS Register
CPL
Segment Selector
For Code Segment
RPL
Destination Code
Segment Descriptor
DPL
Privilege
Check
C
Figure 5-6. Privilege Check for Control Transfer Without Using a Gate
•
•
•
The DPL of the segment descriptor for the destination code segment that contains the called procedure.
The RPL of the segment selector of the destination code segment.
The conforming (C) flag in the segment descriptor for the destination code segment, which determines whether
the segment is a conforming (C flag is set) or nonconforming (C flag is clear) code segment. See Section
3.4.5.1, “Code- and Data-Segment Descriptor Types,” for more information about this flag.
The rules that the processor uses to check the CPL, RPL, and DPL depends on the setting of the C flag, as described
in the following sections.
5.8.1.1
Accessing Nonconforming Code Segments
When accessing nonconforming code segments, the CPL of the calling procedure must be equal to the DPL of the
destination code segment; otherwise, the processor generates a general-protection exception (#GP). For example
in Figure 5-7:
•
Code segment C is a nonconforming code segment. A procedure in code segment A can call a procedure in code
segment C (using segment selector C1) because they are at the same privilege level (CPL of code segment A is
equal to the DPL of code segment C).
•
A procedure in code segment B cannot call a procedure in code segment C (using segment selector C2 or C1)
because the two code segments are at different privilege levels.
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Code
Segment B
CPL=3
3
Segment Sel. D2
RPL=3
Segment Sel. C2
RPL=3
Lowest Privilege
Code
Segment A
CPL=2
Segment Sel. C1
RPL=2
Segment Sel. D1
RPL=2
2
Code
Segment C
DPL=2
Nonconforming
Code Segment
Code
Segment D
DPL=1
Conforming
Code Segment
1
0
Highest Privilege
Figure 5-7. Examples of Accessing Conforming and Nonconforming Code Segments From Various Privilege Levels
The RPL of the segment selector that points to a nonconforming code segment has a limited effect on the privilege
check. The RPL must be numerically less than or equal to the CPL of the calling procedure for a successful control
transfer to occur. So, in the example in Figure 5-7, the RPLs of segment selectors C1 and C2 could legally be set to
0, 1, or 2, but not to 3.
When the segment selector of a nonconforming code segment is loaded into the CS register, the privilege level field
is not changed; that is, it remains at the CPL (which is the privilege level of the calling procedure). This is true, even
if the RPL of the segment selector is different from the CPL.
5.8.1.2
Accessing Conforming Code Segments
When accessing conforming code segments, the CPL of the calling procedure may be numerically equal to or
greater than (less privileged) the DPL of the destination code segment; the processor generates a general-protection exception (#GP) only if the CPL is less than the DPL. (The segment selector RPL for the destination code
segment is not checked if the segment is a conforming code segment.)
In the example in Figure 5-7, code segment D is a conforming code segment. Therefore, calling procedures in both
code segment A and B can access code segment D (using either segment selector D1 or D2, respectively), because
they both have CPLs that are greater than or equal to the DPL of the conforming code segment. For conforming
code segments, the DPL represents the numerically lowest privilege level that a calling procedure may
be at to successfully make a call to the code segment.
(Note that segments selectors D1 and D2 are identical except for their respective RPLs. But since RPLs are not
checked when accessing conforming code segments, the two segment selectors are essentially interchangeable.)
When program control is transferred to a conforming code segment, the CPL does not change, even if the DPL of
the destination code segment is less than the CPL. This situation is the only one where the CPL may be different
from the DPL of the current code segment. Also, since the CPL does not change, no stack switch occurs.
Conforming segments are used for code modules such as math libraries and exception handlers, which support
applications but do not require access to protected system facilities. These modules are part of the operating
system or executive software, but they can be executed at numerically higher privilege levels (less privileged
levels). Keeping the CPL at the level of a calling code segment when switching to a conforming code segment
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prevents an application program from accessing nonconforming code segments while at the privilege level (DPL) of
a conforming code segment and thus prevents it from accessing more privileged data.
Most code segments are nonconforming. For these segments, program control can be transferred only to code
segments at the same level of privilege, unless the transfer is carried out through a call gate, as described in the
following sections.
5.8.2
Gate Descriptors
To provide controlled access to code segments with different privilege levels, the processor provides special set of
descriptors called gate descriptors. There are four kinds of gate descriptors:
•
•
•
•
Call gates
Trap gates
Interrupt gates
Task gates
Task gates are used for task switching and are discussed in Chapter 7, “Task Management”. Trap and interrupt
gates are special kinds of call gates used for calling exception and interrupt handlers. The are described in Chapter
6, “Interrupt and Exception Handling.” This chapter is concerned only with call gates.
5.8.3
Call Gates
Call gates facilitate controlled transfers of program control between different privilege levels. They are typically
used only in operating systems or executives that use the privilege-level protection mechanism. Call gates are also
useful for transferring program control between 16-bit and 32-bit code segments, as described in Section 21.4,
“Transferring Control Among Mixed-Size Code Segments.”
Figure 5-8 shows the format of a call-gate descriptor. A call-gate descriptor may reside in the GDT or in an LDT, but
not in the interrupt descriptor table (IDT). It performs six functions:
•
•
•
It specifies the code segment to be accessed.
It defines an entry point for a procedure in the specified code segment.
It specifies the privilege level required for a caller trying to access the procedure.
31
16 15 14 13 12 11
Offset in Segment 31:16
31
P
D
P
L
8 7
Type
6
0 0 0
0 1 1 0 0
16 15
Segment Selector
0
5 4
Param.
Count
4
0
Offset in Segment 15:00
0
DPL Descriptor Privilege Level
P
Gate Valid
Figure 5-8. Call-Gate Descriptor
•
•
If a stack switch occurs, it specifies the number of optional parameters to be copied between stacks.
•
It specifies whether the call-gate descriptor is valid.
It defines the size of values to be pushed onto the target stack: 16-bit gates force 16-bit pushes and 32-bit
gates force 32-bit pushes.
The segment selector field in a call gate specifies the code segment to be accessed. The offset field specifies the
entry point in the code segment. This entry point is generally to the first instruction of a specific procedure. The
DPL field indicates the privilege level of the call gate, which in turn is the privilege level required to access the
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selected procedure through the gate. The P flag indicates whether the call-gate descriptor is valid. (The presence
of the code segment to which the gate points is indicated by the P flag in the code segment’s descriptor.) The
parameter count field indicates the number of parameters to copy from the calling procedures stack to the new
stack if a stack switch occurs (see Section 5.8.5, “Stack Switching”). The parameter count specifies the number of
words for 16-bit call gates and doublewords for 32-bit call gates.
Note that the P flag in a gate descriptor is normally always set to 1. If it is set to 0, a not present (#NP) exception
is generated when a program attempts to access the descriptor. The operating system can use the P flag for special
purposes. For example, it could be used to track the number of times the gate is used. Here, the P flag is initially
set to 0 causing a trap to the not-present exception handler. The exception handler then increments a counter and
sets the P flag to 1, so that on returning from the handler, the gate descriptor will be valid.
5.8.3.1
IA-32e Mode Call Gates
Call-gate descriptors in 32-bit mode provide a 32-bit offset for the instruction pointer (EIP); 64-bit extensions
double the size of 32-bit mode call gates in order to store 64-bit instruction pointers (RIP). See Figure 5-9:
•
The first eight bytes (bytes 7:0) of a 64-bit mode call gate are similar but not identical to legacy 32-bit mode
call gates. The parameter-copy-count field has been removed.
•
Bytes 11:8 hold the upper 32 bits of the target-segment offset in canonical form. A general-protection
exception (#GP) is generated if software attempts to use a call gate with a target offset that is not in canonical
form.
•
16-byte descriptors may reside in the same descriptor table with 16-bit and 32-bit descriptors. A type field,
used for consistency checking, is defined in bits 12:8 of the 64-bit descriptor’s highest dword (cleared to zero).
A general-protection exception (#GP) results if an attempt is made to access the upper half of a 64-bit mode
descriptor as a 32-bit mode descriptor.
13 12 11 10 9 8 7
31
Type
0
Reserved
Reserved
16
0 0 0 0 0
31
0
8
Offset in Segment 63:31
31
Offset in Segment 31:16
31
P
D
P
L
0
8 7
16 15 14 13 12 11
Type
0
16 15
Segment Selector
.
4
0 1 1 0 0
0
Offset in Segment 15:00
0
DPL Descriptor Privilege Level
P
Gate Valid
Figure 5-9. Call-Gate Descriptor in IA-32e Mode
•
Target code segments referenced by a 64-bit call gate must be 64-bit code segments (CS.L = 1, CS.D = 0). If
not, the reference generates a general-protection exception, #GP (CS selector).
•
Only 64-bit mode call gates can be referenced in IA-32e mode (64-bit mode and compatibility mode). The
legacy 32-bit mode call gate type (0CH) is redefined in IA-32e mode as a 64-bit call-gate type; no 32-bit callgate type exists in IA-32e mode.
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•
If a far call references a 16-bit call gate type (04H) in IA-32e mode, a general-protection exception (#GP) is
generated.
When a call references a 64-bit mode call gate, actions taken are identical to those taken in 32-bit mode, with the
following exceptions:
•
•
•
Stack pushes are made in eight-byte increments.
A 64-bit RIP is pushed onto the stack.
Parameter copying is not performed.
Use a matching far-return instruction size for correct operation (returns from 64-bit calls must be performed with
a 64-bit operand-size return to process the stack correctly).
5.8.4
Accessing a Code Segment Through a Call Gate
To access a call gate, a far pointer to the gate is provided as a target operand in a CALL or JMP instruction. The
segment selector from this pointer identifies the call gate (see Figure 5-10); the offset from the pointer is required,
but not used or checked by the processor. (The offset can be set to any value.)
When the processor has accessed the call gate, it uses the segment selector from the call gate to locate the
segment descriptor for the destination code segment. (This segment descriptor can be in the GDT or the LDT.) It
then combines the base address from the code-segment descriptor with the offset from the call gate to form the
linear address of the procedure entry point in the code segment.
As shown in Figure 5-11, four different privilege levels are used to check the validity of a program control transfer
through a call gate:
•
•
•
•
The CPL (current privilege level).
The RPL (requestor's privilege level) of the call gate’s selector.
The DPL (descriptor privilege level) of the call gate descriptor.
The DPL of the segment descriptor of the destination code segment.
The C flag (conforming) in the segment descriptor for the destination code segment is also checked.
Far Pointer to Call Gate
Segment Selector
Offset
Required but not used by processor
Descriptor Table
Offset
Segment Selector
Base
+
Offset
Base
Base
Call-Gate
Descriptor
Code-Segment
Descriptor
Procedure
Entry Point
Figure 5-10. Call-Gate Mechanism
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CS Register
CPL
Call-Gate Selector
RPL
Call Gate (Descriptor)
DPL
Privilege
Check
Destination CodeSegment Descriptor
DPL
Figure 5-11. Privilege Check for Control Transfer with Call Gate
The privilege checking rules are different depending on whether the control transfer was initiated with a CALL or a
JMP instruction, as shown in Table 5-1.
Table 5-1. Privilege Check Rules for Call Gates
Instruction
Privilege Check Rules
CALL
CPL ≤ call gate DPL; RPL ≤ call gate DPL
Destination conforming code segment DPL ≤ CPL
Destination nonconforming code segment DPL ≤ CPL
JMP
CPL ≤ call gate DPL; RPL ≤ call gate DPL
Destination conforming code segment DPL ≤ CPL
Destination nonconforming code segment DPL = CPL
The DPL field of the call-gate descriptor specifies the numerically highest privilege level from which a calling procedure can access the call gate; that is, to access a call gate, the CPL of a calling procedure must be equal to or less
than the DPL of the call gate. For example, in Figure 5-15, call gate A has a DPL of 3. So calling procedures at all
CPLs (0 through 3) can access this call gate, which includes calling procedures in code segments A, B, and C. Call
gate B has a DPL of 2, so only calling procedures at a CPL or 0, 1, or 2 can access call gate B, which includes calling
procedures in code segments B and C. The dotted line shows that a calling procedure in code segment A cannot
access call gate B.
The RPL of the segment selector to a call gate must satisfy the same test as the CPL of the calling procedure; that
is, the RPL must be less than or equal to the DPL of the call gate. In the example in Figure 5-15, a calling procedure
in code segment C can access call gate B using gate selector B2 or B1, but it could not use gate selector B3 to
access call gate B.
If the privilege checks between the calling procedure and call gate are successful, the processor then checks the
DPL of the code-segment descriptor against the CPL of the calling procedure. Here, the privilege check rules vary
between CALL and JMP instructions. Only CALL instructions can use call gates to transfer program control to more
privileged (numerically lower privilege level) nonconforming code segments; that is, to nonconforming code
segments with a DPL less than the CPL. A JMP instruction can use a call gate only to transfer program control to a
nonconforming code segment with a DPL equal to the CPL. CALL and JMP instruction can both transfer program
control to a more privileged conforming code segment; that is, to a conforming code segment with a DPL less than
or equal to the CPL.
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If a call is made to a more privileged (numerically lower privilege level) nonconforming destination code segment,
the CPL is lowered to the DPL of the destination code segment and a stack switch occurs (see Section 5.8.5, “Stack
Switching”). If a call or jump is made to a more privileged conforming destination code segment, the CPL is not
changed and no stack switch occurs.
3
Code
Segment A
Gate Selector A
RPL=3
CPL=3
Gate Selector B3
RPL=3
Call
Gate A
DPL=3
Lowest Privilege
Code
Segment B
CPL=2
Gate Selector B1
RPL=2
Call
Gate B
DPL=2
2
Code
Segment C
CPL=1
Gate Selector B2
RPL=1
No Stack
Switch Occurs
1
Stack Switch
Occurs
Code
Segment D
DPL=0
0
Highest Privilege
Conforming
Code Segment
Code
Segment E
DPL=0
Nonconforming
Code Segment
Figure 5-12. Example of Accessing Call Gates At Various Privilege Levels
Call gates allow a single code segment to have procedures that can be accessed at different privilege levels. For
example, an operating system located in a code segment may have some services which are intended to be used
by both the operating system and application software (such as procedures for handling character I/O). Call gates
for these procedures can be set up that allow access at all privilege levels (0 through 3). More privileged call gates
(with DPLs of 0 or 1) can then be set up for other operating system services that are intended to be used only by
the operating system (such as procedures that initialize device drivers).
5.8.5
Stack Switching
Whenever a call gate is used to transfer program control to a more privileged nonconforming code segment (that
is, when the DPL of the nonconforming destination code segment is less than the CPL), the processor automatically
switches to the stack for the destination code segment’s privilege level. This stack switching is carried out to
prevent more privileged procedures from crashing due to insufficient stack space. It also prevents less privileged
procedures from interfering (by accident or intent) with more privileged procedures through a shared stack.
Each task must define up to 4 stacks: one for applications code (running at privilege level 3) and one for each of
the privilege levels 2, 1, and 0 that are used. (If only two privilege levels are used [3 and 0], then only two stacks
must be defined.) Each of these stacks is located in a separate segment and is identified with a segment selector
and an offset into the stack segment (a stack pointer).
The segment selector and stack pointer for the privilege level 3 stack is located in the SS and ESP registers, respectively, when privilege-level-3 code is being executed and is automatically stored on the called procedure’s stack
when a stack switch occurs.
Pointers to the privilege level 0, 1, and 2 stacks are stored in the TSS for the currently running task (see
Figure 7-2). Each of these pointers consists of a segment selector and a stack pointer (loaded into the ESP
register). These initial pointers are strictly read-only values. The processor does not change them while the task is
running. They are used only to create new stacks when calls are made to more privileged levels (numerically lower
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privilege levels). These stacks are disposed of when a return is made from the called procedure. The next time the
procedure is called, a new stack is created using the initial stack pointer. (The TSS does not specify a stack for privilege level 3 because the processor does not allow a transfer of program control from a procedure running at a CPL
of 0, 1, or 2 to a procedure running at a CPL of 3, except on a return.)
The operating system is responsible for creating stacks and stack-segment descriptors for all the privilege levels to
be used and for loading initial pointers for these stacks into the TSS. Each stack must be read/write accessible (as
specified in the type field of its segment descriptor) and must contain enough space (as specified in the limit field)
to hold the following items:
•
•
•
The contents of the SS, ESP, CS, and EIP registers for the calling procedure.
The parameters and temporary variables required by the called procedure.
The EFLAGS register and error code, when implicit calls are made to an exception or interrupt handler.
The stack will need to require enough space to contain many frames of these items, because procedures often call
other procedures, and an operating system may support nesting of multiple interrupts. Each stack should be large
enough to allow for the worst case nesting scenario at its privilege level.
(If the operating system does not use the processor’s multitasking mechanism, it still must create at least one TSS
for this stack-related purpose.)
When a procedure call through a call gate results in a change in privilege level, the processor performs the
following steps to switch stacks and begin execution of the called procedure at a new privilege level:
1. Uses the DPL of the destination code segment (the new CPL) to select a pointer to the new stack (segment
selector and stack pointer) from the TSS.
2. Reads the segment selector and stack pointer for the stack to be switched to from the current TSS. Any limit
violations detected while reading the stack-segment selector, stack pointer, or stack-segment descriptor cause
an invalid TSS (#TS) exception to be generated.
3. Checks the stack-segment descriptor for the proper privileges and type and generates an invalid TSS (#TS)
exception if violations are detected.
4. Temporarily saves the current values of the SS and ESP registers.
5. Loads the segment selector and stack pointer for the new stack in the SS and ESP registers.
6. Pushes the temporarily saved values for the SS and ESP registers (for the calling procedure) onto the new stack
(see Figure 5-13).
7. Copies the number of parameter specified in the parameter count field of the call gate from the calling
procedure’s stack to the new stack. If the count is 0, no parameters are copied.
8. Pushes the return instruction pointer (the current contents of the CS and EIP registers) onto the new stack.
9. Loads the segment selector for the new code segment and the new instruction pointer from the call gate into
the CS and EIP registers, respectively, and begins execution of the called procedure.
See the description of the CALL instruction in Chapter 3, Instruction Set Reference, in the IA-32 Intel Architecture
Software Developer’s Manual, Volume 2, for a detailed description of the privilege level checks and other protection
checks that the processor performs on a far call through a call gate.
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Calling Procedure’s Stack
Called Procedure’s Stack
Calling SS
Parameter 1
Calling ESP
Parameter 2
Parameter 1
Parameter 3
ESP
Parameter 2
Parameter 3
Calling CS
Calling EIP
ESP
Figure 5-13. Stack Switching During an Interprivilege-Level Call
The parameter count field in a call gate specifies the number of data items (up to 31) that the processor should
copy from the calling procedure’s stack to the stack of the called procedure. If more than 31 data items need to be
passed to the called procedure, one of the parameters can be a pointer to a data structure, or the saved contents
of the SS and ESP registers may be used to access parameters in the old stack space. The size of the data items
passed to the called procedure depends on the call gate size, as described in Section 5.8.3, “Call Gates.”
5.8.5.1
Stack Switching in 64-bit Mode
Although protection-check rules for call gates are unchanged from 32-bit mode, stack-switch changes in 64-bit
mode are different.
When stacks are switched as part of a 64-bit mode privilege-level change through a call gate, a new SS (stack
segment) descriptor is not loaded; 64-bit mode only loads an inner-level RSP from the TSS. The new SS is forced
to NULL and the SS selector’s RPL field is forced to the new CPL. The new SS is set to NULL in order to handle
nested far transfers (CALLF, INTn, interrupts and exceptions). The old SS and RSP are saved on the new stack.
On a subsequent RETF, the old SS is popped from the stack and loaded into the SS register. See Table 5-2.
Table 5-2. 64-Bit-Mode Stack Layout After CALLF with CPL Change
32-bit Mode
IA-32e mode
Old SS Selector
+12
+24
Old SS Selector
Old ESP
+8
+16
Old RSP
CS Selector
+4
+8
Old CS Selector
EIP
0
0
RIP
< 4 Bytes >
ESP
RSP
< 8 Bytes >
In 64-bit mode, stack operations resulting from a privilege-level-changing far call or far return are eight-bytes wide
and change the RSP by eight. The mode does not support the automatic parameter-copy feature found in 32-bit
mode. The call-gate count field is ignored. Software can access the old stack, if necessary, by referencing the old
stack-segment selector and stack pointer saved on the new process stack.
In 64-bit mode, RETF is allowed to load a NULL SS under certain conditions. If the target mode is 64-bit mode and
the target CPL< >3, IRET allows SS to be loaded with a NULL selector. If the called procedure itself is interrupted,
the NULL SS is pushed on the stack frame. On the subsequent RETF, the NULL SS on the stack acts as a flag to tell
the processor not to load a new SS descriptor.
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5.8.6
Returning from a Called Procedure
The RET instruction can be used to perform a near return, a far return at the same privilege level, and a far return
to a different privilege level. This instruction is intended to execute returns from procedures that were called with
a CALL instruction. It does not support returns from a JMP instruction, because the JMP instruction does not save a
return instruction pointer on the stack.
A near return only transfers program control within the current code segment; therefore, the processor performs
only a limit check. When the processor pops the return instruction pointer from the stack into the EIP register, it
checks that the pointer does not exceed the limit of the current code segment.
On a far return at the same privilege level, the processor pops both a segment selector for the code segment being
returned to and a return instruction pointer from the stack. Under normal conditions, these pointers should be
valid, because they were pushed on the stack by the CALL instruction. However, the processor performs privilege
checks to detect situations where the current procedure might have altered the pointer or failed to maintain the
stack properly.
A far return that requires a privilege-level change is only allowed when returning to a less privileged level (that is,
the DPL of the return code segment is numerically greater than the CPL). The processor uses the RPL field from the
CS register value saved for the calling procedure (see Figure 5-13) to determine if a return to a numerically higher
privilege level is required. If the RPL is numerically greater (less privileged) than the CPL, a return across privilege
levels occurs.
The processor performs the following steps when performing a far return to a calling procedure (see Figures 6-2
and 6-4 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, for an illustration of the
stack contents prior to and after a return):
1. Checks the RPL field of the saved CS register value to determine if a privilege level change is required on the
return.
2. Loads the CS and EIP registers with the values on the called procedure’s stack. (Type and privilege level checks
are performed on the code-segment descriptor and RPL of the code- segment selector.)
3. (If the RET instruction includes a parameter count operand and the return requires a privilege level change.)
Adds the parameter count (in bytes obtained from the RET instruction) to the current ESP register value (after
popping the CS and EIP values), to step past the parameters on the called procedure’s stack. The resulting
value in the ESP register points to the saved SS and ESP values for the calling procedure’s stack. (Note that the
byte count in the RET instruction must be chosen to match the parameter count in the call gate that the calling
procedure referenced when it made the original call multiplied by the size of the parameters.)
4. (If the return requires a privilege level change.) Loads the SS and ESP registers with the saved SS and ESP
values and switches back to the calling procedure’s stack. The SS and ESP values for the called procedure’s
stack are discarded. Any limit violations detected while loading the stack-segment selector or stack pointer
cause a general-protection exception (#GP) to be generated. The new stack-segment descriptor is also
checked for type and privilege violations.
5. (If the RET instruction includes a parameter count operand.) Adds the parameter count (in bytes obtained from
the RET instruction) to the current ESP register value, to step past the parameters on the calling procedure’s
stack. The resulting ESP value is not checked against the limit of the stack segment. If the ESP value is beyond
the limit, that fact is not recognized until the next stack operation.
6. (If the return requires a privilege level change.) Checks the contents of the DS, ES, FS, and GS segment
registers. If any of these registers refer to segments whose DPL is less than the new CPL (excluding conforming
code segments), the segment register is loaded with a null segment selector.
See the description of the RET instruction in Chapter 4 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2B, for a detailed description of the privilege level checks and other protection checks that
the processor performs on a far return.
5.8.7
Performing Fast Calls to System Procedures with the
SYSENTER and SYSEXIT Instructions
The SYSENTER and SYSEXIT instructions were introduced into the IA-32 architecture in the Pentium II processors
for the purpose of providing a fast (low overhead) mechanism for calling operating system or executive procedures.
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SYSENTER is intended for use by user code running at privilege level 3 to access operating system or executive
procedures running at privilege level 0. SYSEXIT is intended for use by privilege level 0 operating system or executive procedures for fast returns to privilege level 3 user code. SYSENTER can be executed from privilege levels 3,
2, 1, or 0; SYSEXIT can only be executed from privilege level 0.
The SYSENTER and SYSEXIT instructions are companion instructions, but they do not constitute a call/return pair.
This is because SYSENTER does not save any state information for use by SYSEXIT on a return.
The target instruction and stack pointer for these instructions are not specified through instruction operands.
Instead, they are specified through parameters entered in MSRs and general-purpose registers.
For SYSENTER, target fields are generated using the following sources:
•
•
•
•
Target code segment — Reads this from IA32_SYSENTER_CS.
Target instruction — Reads this from IA32_SYSENTER_EIP.
Stack segment — Computed by adding 8 to the value in IA32_SYSENTER_CS.
Stack pointer — Reads this from the IA32_SYSENTER_ESP.
For SYSEXIT, target fields are generated using the following sources:
•
•
•
•
Target code segment — Computed by adding 16 to the value in the IA32_SYSENTER_CS.
Target instruction — Reads this from EDX.
Stack segment — Computed by adding 24 to the value in IA32_SYSENTER_CS.
Stack pointer — Reads this from ECX.
The SYSENTER and SYSEXIT instructions preform “fast” calls and returns because they force the processor into a
predefined privilege level 0 state when SYSENTER is executed and into a predefined privilege level 3 state when
SYSEXIT is executed. By forcing predefined and consistent processor states, the number of privilege checks ordinarily required to perform a far call to another privilege levels are greatly reduced. Also, by predefining the target
context state in MSRs and general-purpose registers eliminates all memory accesses except when fetching the
target code.
Any additional state that needs to be saved to allow a return to the calling procedure must be saved explicitly by
the calling procedure or be predefined through programming conventions.
5.8.7.1
SYSENTER and SYSEXIT Instructions in IA-32e Mode
For Intel 64 processors, the SYSENTER and SYSEXIT instructions are enhanced to allow fast system calls from user
code running at privilege level 3 (in compatibility mode or 64-bit mode) to 64-bit executive procedures running at
privilege level 0. IA32_SYSENTER_EIP MSR and IA32_SYSENTER_ESP MSR are expanded to hold 64-bit addresses.
If IA-32e mode is inactive, only the lower 32-bit addresses stored in these MSRs are used. The WRMSR instruction
ensures that the addresses stored in these MSRs are canonical. Note that, in 64-bit mode, IA32_SYSENTER_CS
must not contain a NULL selector.
When SYSENTER transfers control, the following fields are generated and bits set:
•
•
•
•
•
•
Target code segment — Reads non-NULL selector from IA32_SYSENTER_CS.
New CS attributes — CS base = 0, CS limit = FFFFFFFFH.
Target instruction — Reads 64-bit canonical address from IA32_SYSENTER_EIP.
Stack segment — Computed by adding 8 to the value from IA32_SYSENTER_CS.
Stack pointer — Reads 64-bit canonical address from IA32_SYSENTER_ESP.
New SS attributes — SS base = 0, SS limit = FFFFFFFFH.
When the SYSEXIT instruction transfers control to 64-bit mode user code using REX.W, the following fields are
generated and bits set:
•
•
•
•
Target code segment — Computed by adding 32 to the value in IA32_SYSENTER_CS.
New CS attributes — L-bit = 1 (go to 64-bit mode).
Target instruction — Reads 64-bit canonical address in RDX.
Stack segment — Computed by adding 40 to the value of IA32_SYSENTER_CS.
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•
Stack pointer — Update RSP using 64-bit canonical address in RCX.
When SYSEXIT transfers control to compatibility mode user code when the operand size attribute is 32 bits, the
following fields are generated and bits set:
•
•
•
•
•
Target code segment — Computed by adding 16 to the value in IA32_SYSENTER_CS.
New CS attributes — L-bit = 0 (go to compatibility mode).
Target instruction — Fetch the target instruction from 32-bit address in EDX.
Stack segment — Computed by adding 24 to the value in IA32_SYSENTER_CS.
Stack pointer — Update ESP from 32-bit address in ECX.
5.8.8
Fast System Calls in 64-Bit Mode
The SYSCALL and SYSRET instructions are designed for operating systems that use a flat memory model (segmentation is not used). The instructions, along with SYSENTER and SYSEXIT, are suited for IA-32e mode operation.
SYSCALL and SYSRET, however, are not supported in compatibility mode (or in protected mode). Use CPUID to
check if SYSCALL and SYSRET are available (CPUID.80000001H.EDX[bit 11] = 1).
SYSCALL is intended for use by user code running at privilege level 3 to access operating system or executive
procedures running at privilege level 0. SYSRET is intended for use by privilege level 0 operating system or executive procedures for fast returns to privilege level 3 user code.
Stack pointers for SYSCALL/SYSRET are not specified through model specific registers. The clearing of bits in
RFLAGS is programmable rather than fixed. SYSCALL/SYSRET save and restore the RFLAGS register.
For SYSCALL, the processor saves RFLAGS into R11 and the RIP of the next instruction into RCX; it then gets the
privilege-level 0 target code segment, instruction pointer, stack segment, and flags as follows:
•
•
Target code segment — Reads a non-NULL selector from IA32_STAR[47:32].
•
•
Stack segment — Computed by adding 8 to the value in IA32_STAR[47:32].
Target instruction pointer — Reads a 64-bit address from IA32_LSTAR. (The WRMSR instruction ensures
that the value of the IA32_LSTAR MSR is canonical.)
Flags — The processor sets RFLAGS to the logical-AND of its current value with the complement of the value in
the IA32_FMASK MSR.
When SYSRET transfers control to 64-bit mode user code using REX.W, the processor gets the privilege level 3
target code segment, instruction pointer, stack segment, and flags as follows:
•
•
•
•
Target code segment — Reads a non-NULL selector from IA32_STAR[63:48] + 16.
Target instruction pointer — Copies the value in RCX into RIP.
Stack segment — IA32_STAR[63:48] + 8.
EFLAGS — Loaded from R11.
When SYSRET transfers control to 32-bit mode user code using a 32-bit operand size, the processor gets the privilege level 3 target code segment, instruction pointer, stack segment, and flags as follows:
•
•
•
•
Target code segment — Reads a non-NULL selector from IA32_STAR[63:48].
Target instruction pointer — Copies the value in ECX into EIP.
Stack segment — IA32_STAR[63:48] + 8.
EFLAGS — Loaded from R11.
It is the responsibility of the OS to ensure the descriptors in the GDT/LDT correspond to the selectors loaded by
SYSCALL/SYSRET (consistent with the base, limit, and attribute values forced by the instructions).
See Figure 5-14 for the layout of IA32_STAR, IA32_LSTAR and IA32_FMASK.
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63
0
32 31
SYSCALL EFLAGS Mask
Reserved
IA32_FMASK
63
0
Target RIP for 64-bit Mode Calling Program
IA32_LSTAR
63
32 31
48 47
SYSRET CS and SS
SYSCALL CS and SS
0
Reserved
IA32_STAR
Figure 5-14. MSRs Used by SYSCALL and SYSRET
The SYSCALL instruction does not save the stack pointer, and the SYSRET instruction does not restore it. It is likely
that the OS system-call handler will change the stack pointer from the user stack to the OS stack. If so, it is the
responsibility of software first to save the user stack pointer. This might be done by user code, prior to executing
SYSCALL, or by the OS system-call handler after SYSCALL.
Because the SYSRET instruction does not modify the stack pointer, it is necessary for software to switch back to the
user stack. The OS may load the user stack pointer (if it was saved after SYSCALL) before executing SYSRET; alternatively, user code may load the stack pointer (if it was saved before SYSCALL) after receiving control from
SYSRET.
If the OS loads the stack pointer before executing SYSRET, it must ensure that the handler of any interrupt or
exception delivered between restoring the stack pointer and successful execution of SYSRET is not invoked with the
user stack. It can do so using approaches such as the following:
•
External interrupts. The OS can prevent an external interrupt from being delivered by clearing EFLAGS.IF
before loading the user stack pointer.
•
Nonmaskable interrupts (NMIs). The OS can ensure that the NMI handler is invoked with the correct stack by
using the interrupt stack table (IST) mechanism for gate 2 (NMI) in the IDT (see Section 6.14.5, “Interrupt
Stack Table”).
•
General-protection exceptions (#GP). The SYSRET instruction generates #GP(0) if the value of RCX is not
canonical. The OS can address this possibility using one or more of the following approaches:
— Confirming that the value of RCX is canonical before executing SYSRET.
— Using paging to ensure that the SYSCALL instruction will never save a non-canonical value into RCX.
— Using the IST mechanism for gate 13 (#GP) in the IDT.
5.9
PRIVILEGED INSTRUCTIONS
Some of the system instructions (called “privileged instructions”) are protected from use by application programs.
The privileged instructions control system functions (such as the loading of system registers). They can be
executed only when the CPL is 0 (most privileged). If one of these instructions is executed when the CPL is not 0,
a general-protection exception (#GP) is generated. The following system instructions are privileged instructions:
•
•
LGDT — Load GDT register.
LLDT — Load LDT register.
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•
•
•
•
•
•
•
•
•
•
•
•
•
•
LTR — Load task register.
LIDT — Load IDT register.
MOV (control registers) — Load and store control registers.
LMSW — Load machine status word.
CLTS — Clear task-switched flag in register CR0.
MOV (debug registers) — Load and store debug registers.
INVD — Invalidate cache, without writeback.
WBINVD — Invalidate cache, with writeback.
INVLPG —Invalidate TLB entry.
HLT— Halt processor.
RDMSR — Read Model-Specific Registers.
WRMSR —Write Model-Specific Registers.
RDPMC — Read Performance-Monitoring Counter.
RDTSC — Read Time-Stamp Counter.
Some of the privileged instructions are available only in the more recent families of Intel 64 and IA-32 processors
(see Section 22.13, “New Instructions In the Pentium and Later IA-32 Processors”).
The PCE and TSD flags in register CR4 (bits 4 and 2, respectively) enable the RDPMC and RDTSC instructions,
respectively, to be executed at any CPL.
5.10
POINTER VALIDATION
When operating in protected mode, the processor validates all pointers to enforce protection between segments
and maintain isolation between privilege levels. Pointer validation consists of the following checks:
1. Checking access rights to determine if the segment type is compatible with its use.
2. Checking read/write rights.
3. Checking if the pointer offset exceeds the segment limit.
4. Checking if the supplier of the pointer is allowed to access the segment.
5. Checking the offset alignment.
The processor automatically performs first, second, and third checks during instruction execution. Software must
explicitly request the fourth check by issuing an ARPL instruction. The fifth check (offset alignment) is performed
automatically at privilege level 3 if alignment checking is turned on. Offset alignment does not affect isolation of
privilege levels.
5.10.1
Checking Access Rights (LAR Instruction)
When the processor accesses a segment using a far pointer, it performs an access rights check on the segment
descriptor pointed to by the far pointer. This check is performed to determine if type and privilege level (DPL) of the
segment descriptor are compatible with the operation to be performed. For example, when making a far call in
protected mode, the segment-descriptor type must be for a conforming or nonconforming code segment, a call
gate, a task gate, or a TSS. Then, if the call is to a nonconforming code segment, the DPL of the code segment must
be equal to the CPL, and the RPL of the code segment’s segment selector must be less than or equal to the DPL. If
type or privilege level are found to be incompatible, the appropriate exception is generated.
To prevent type incompatibility exceptions from being generated, software can check the access rights of a
segment descriptor using the LAR (load access rights) instruction. The LAR instruction specifies the segment
selector for the segment descriptor whose access rights are to be checked and a destination register. The instruction then performs the following operations:
1. Check that the segment selector is not null.
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2. Checks that the segment selector points to a segment descriptor that is within the descriptor table limit (GDT
or LDT).
3. Checks that the segment descriptor is a code, data, LDT, call gate, task gate, or TSS segment-descriptor type.
4. If the segment is not a conforming code segment, checks if the segment descriptor is visible at the CPL (that
is, if the CPL and the RPL of the segment selector are less than or equal to the DPL).
5. If the privilege level and type checks pass, loads the second doubleword of the segment descriptor into the
destination register (masked by the value 00FXFF00H, where X indicates that the corresponding 4 bits are
undefined) and sets the ZF flag in the EFLAGS register. If the segment selector is not visible at the current
privilege level or is an invalid type for the LAR instruction, the instruction does not modify the destination
register and clears the ZF flag.
Once loaded in the destination register, software can preform additional checks on the access rights information.
5.10.2
Checking Read/Write Rights (VERR and VERW Instructions)
When the processor accesses any code or data segment it checks the read/write privileges assigned to the
segment to verify that the intended read or write operation is allowed. Software can check read/write rights using
the VERR (verify for reading) and VERW (verify for writing) instructions. Both these instructions specify the
segment selector for the segment being checked. The instructions then perform the following operations:
1. Check that the segment selector is not null.
2. Checks that the segment selector points to a segment descriptor that is within the descriptor table limit (GDT
or LDT).
3. Checks that the segment descriptor is a code or data-segment descriptor type.
4. If the segment is not a conforming code segment, checks if the segment descriptor is visible at the CPL (that
is, if the CPL and the RPL of the segment selector are less than or equal to the DPL).
5. Checks that the segment is readable (for the VERR instruction) or writable (for the VERW) instruction.
The VERR instruction sets the ZF flag in the EFLAGS register if the segment is visible at the CPL and readable; the
VERW sets the ZF flag if the segment is visible and writable. (Code segments are never writable.) The ZF flag is
cleared if any of these checks fail.
5.10.3
Checking That the Pointer Offset Is Within Limits (LSL Instruction)
When the processor accesses any segment it performs a limit check to insure that the offset is within the limit of
the segment. Software can perform this limit check using the LSL (load segment limit) instruction. Like the LAR
instruction, the LSL instruction specifies the segment selector for the segment descriptor whose limit is to be
checked and a destination register. The instruction then performs the following operations:
1. Check that the segment selector is not null.
2. Checks that the segment selector points to a segment descriptor that is within the descriptor table limit (GDT
or LDT).
3. Checks that the segment descriptor is a code, data, LDT, or TSS segment-descriptor type.
4. If the segment is not a conforming code segment, checks if the segment descriptor is visible at the CPL (that
is, if the CPL and the RPL of the segment selector less than or equal to the DPL).
5. If the privilege level and type checks pass, loads the unscrambled limit (the limit scaled according to the setting
of the G flag in the segment descriptor) into the destination register and sets the ZF flag in the EFLAGS register.
If the segment selector is not visible at the current privilege level or is an invalid type for the LSL instruction,
the instruction does not modify the destination register and clears the ZF flag.
Once loaded in the destination register, software can compare the segment limit with the offset of a pointer.
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5.10.4
Checking Caller Access Privileges (ARPL Instruction)
The requestor’s privilege level (RPL) field of a segment selector is intended to carry the privilege level of a calling
procedure (the calling procedure’s CPL) to a called procedure. The called procedure then uses the RPL to determine
if access to a segment is allowed. The RPL is said to “weaken” the privilege level of the called procedure to that of
the RPL.
Operating-system procedures typically use the RPL to prevent less privileged application programs from accessing
data located in more privileged segments. When an operating-system procedure (the called procedure) receives a
segment selector from an application program (the calling procedure), it sets the segment selector’s RPL to the
privilege level of the calling procedure. Then, when the operating system uses the segment selector to access its
associated segment, the processor performs privilege checks using the calling procedure’s privilege level (stored in
the RPL) rather than the numerically lower privilege level (the CPL) of the operating-system procedure. The RPL
thus insures that the operating system does not access a segment on behalf of an application program unless that
program itself has access to the segment.
Figure 5-15 shows an example of how the processor uses the RPL field. In this example, an application program
(located in code segment A) possesses a segment selector (segment selector D1) that points to a privileged data
structure (that is, a data structure located in a data segment D at privilege level 0).
The application program cannot access data segment D, because it does not have sufficient privilege, but the operating system (located in code segment C) can. So, in an attempt to access data segment D, the application
program executes a call to the operating system and passes segment selector D1 to the operating system as a
parameter on the stack. Before passing the segment selector, the (well behaved) application program sets the RPL
of the segment selector to its current privilege level (which in this example is 3). If the operating system attempts
to access data segment D using segment selector D1, the processor compares the CPL (which is now 0 following
the call), the RPL of segment selector D1, and the DPL of data segment D (which is 0). Since the RPL is greater than
the DPL, access to data segment D is denied. The processor’s protection mechanism thus protects data segment D
from access by the operating system, because application program’s privilege level (represented by the RPL of
segment selector B) is greater than the DPL of data segment D.
Passed as a
parameter on
the stack.
Application Program
Code
Segment A
CPL=3
3
Gate Selector B
RPL=3
Call
Gate B
Segment Sel. D1
RPL=3
DPL=3
Lowest Privilege
2
Access
not
allowed
1
Code
Operating Segment C
System
DPL=0
0
Highest Privilege
Segment Sel. D2
RPL=0
Access
allowed
Data
Segment D
DPL=0
Figure 5-15. Use of RPL to Weaken Privilege Level of Called Procedure
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Now assume that instead of setting the RPL of the segment selector to 3, the application program sets the RPL to
0 (segment selector D2). The operating system can now access data segment D, because its CPL and the RPL of
segment selector D2 are both equal to the DPL of data segment D.
Because the application program is able to change the RPL of a segment selector to any value, it can potentially use
a procedure operating at a numerically lower privilege level to access a protected data structure. This ability to
lower the RPL of a segment selector breaches the processor’s protection mechanism.
Because a called procedure cannot rely on the calling procedure to set the RPL correctly, operating-system procedures (executing at numerically lower privilege-levels) that receive segment selectors from numerically higher
privilege-level procedures need to test the RPL of the segment selector to determine if it is at the appropriate level.
The ARPL (adjust requested privilege level) instruction is provided for this purpose. This instruction adjusts the RPL
of one segment selector to match that of another segment selector.
The example in Figure 5-15 demonstrates how the ARPL instruction is intended to be used. When the operatingsystem receives segment selector D2 from the application program, it uses the ARPL instruction to compare the
RPL of the segment selector with the privilege level of the application program (represented by the code-segment
selector pushed onto the stack). If the RPL is less than application program’s privilege level, the ARPL instruction
changes the RPL of the segment selector to match the privilege level of the application program (segment selector
D1). Using this instruction thus prevents a procedure running at a numerically higher privilege level from
accessing numerically lower privilege-level (more privileged) segments by lowering the RPL of a segment selector.
Note that the privilege level of the application program can be determined by reading the RPL field of the segment
selector for the application-program’s code segment. This segment selector is stored on the stack as part of the call
to the operating system. The operating system can copy the segment selector from the stack into a register for
use as an operand for the ARPL instruction.
5.10.5
Checking Alignment
When the CPL is 3, alignment of memory references can be checked by setting the AM flag in the CR0 register and
the AC flag in the EFLAGS register. Unaligned memory references generate alignment exceptions (#AC). The
processor does not generate alignment exceptions when operating at privilege level 0, 1, or 2. See Table 6-7 for a
description of the alignment requirements when alignment checking is enabled.
5.11
PAGE-LEVEL PROTECTION
Page-level protection can be used alone or applied to segments. When page-level protection is used with the flat
memory model, it allows supervisor code and data (the operating system or executive) to be protected from user
code and data (application programs). It also allows pages containing code to be write protected. When the
segment- and page-level protection are combined, page-level read/write protection allows more protection granularity within segments.
With page-level protection (as with segment-level protection) each memory reference is checked to verify that
protection checks are satisfied. All checks are made before the memory cycle is started, and any violation prevents
the cycle from starting and results in a page-fault exception being generated. Because checks are performed in
parallel with address translation, there is no performance penalty.
The processor performs two page-level protection checks:
•
•
Restriction of addressable domain (supervisor and user modes).
Page type (read only or read/write).
Violations of either of these checks results in a page-fault exception being generated. See Chapter 6, “Interrupt
14—Page-Fault Exception (#PF),” for an explanation of the page-fault exception mechanism. This chapter
describes the protection violations which lead to page-fault exceptions.
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5.11.1
Page-Protection Flags
Protection information for pages is contained in two flags in a paging-structure entry (see Chapter 4): the
read/write flag (bit 1) and the user/supervisor flag (bit 2). The protection checks use the flags in all paging structures.
5.11.2
Restricting Addressable Domain
The page-level protection mechanism allows restricting access to pages based on two privilege levels:
•
Supervisor mode (U/S flag is 0)—(Most privileged) For the operating system or executive, other system
software (such as device drivers), and protected system data (such as page tables).
•
User mode (U/S flag is 1)—(Least privileged) For application code and data.
The segment privilege levels map to the page privilege levels as follows. If the processor is currently operating at
a CPL of 0, 1, or 2, it is in supervisor mode; if it is operating at a CPL of 3, it is in user mode. When the processor is
in supervisor mode, it can access all pages; when in user mode, it can access only user-level pages. (Note that the
WP flag in control register CR0 modifies the supervisor permissions, as described in Section 5.11.3, “Page Type.”)
Note that to use the page-level protection mechanism, code and data segments must be set up for at least two
segment-based privilege levels: level 0 for supervisor code and data segments and level 3 for user code and data
segments. (In this model, the stacks are placed in the data segments.) To minimize the use of segments, a flat
memory model can be used (see Section 3.2.1, “Basic Flat Model”).
Here, the user and supervisor code and data segments all begin at address zero in the linear address space and
overlay each other. With this arrangement, operating-system code (running at the supervisor level) and application
code (running at the user level) can execute as if there are no segments. Protection between operating-system and
application code and data is provided by the processor’s page-level protection mechanism.
5.11.3
Page Type
The page-level protection mechanism recognizes two page types:
•
•
Read-only access (R/W flag is 0).
Read/write access (R/W flag is 1).
When the processor is in supervisor mode and the WP flag in register CR0 is clear (its state following reset initialization), all pages are both readable and writable (write-protection is ignored). When the processor is in user
mode, it can write only to user-mode pages that are read/write accessible. User-mode pages which are read/write
or read-only are readable; supervisor-mode pages are neither readable nor writable from user mode. A page-fault
exception is generated on any attempt to violate the protection rules.
Starting with the P6 family, Intel processors allow user-mode pages to be write-protected against supervisor-mode
access. Setting CR0.WP = 1 enables supervisor-mode sensitivity to write protected pages. If CR0.WP = 1, readonly pages are not writable from any privilege level. This supervisor write-protect feature is useful for implementing a “copy-on-write” strategy used by some operating systems, such as UNIX*, for task creation (also called
forking or spawning). When a new task is created, it is possible to copy the entire address space of the parent task.
This gives the child task a complete, duplicate set of the parent's segments and pages. An alternative copy-onwrite strategy saves memory space and time by mapping the child's segments and pages to the same segments
and pages used by the parent task. A private copy of a page gets created only when one of the tasks writes to the
page. By using the WP flag and marking the shared pages as read-only, the supervisor can detect an attempt to
write to a page, and can copy the page at that time.
5.11.4
Combining Protection of Both Levels of Page Tables
For any one page, the protection attributes of its page-directory entry (first-level page table) may differ from those
of its page-table entry (second-level page table). The processor checks the protection for a page in both its pagedirectory and the page-table entries. Table 5-3 shows the protection provided by the possible combinations of
protection attributes when the WP flag is clear.
5-28 Vol. 3A
PROTECTION
5.11.5
Overrides to Page Protection
The following types of memory accesses are checked as if they are privilege-level 0 accesses, regardless of the CPL
at which the processor is currently operating:
•
•
Access to segment descriptors in the GDT, LDT, or IDT.
Access to an inner-privilege-level stack during an inter-privilege-level call or a call to in exception or interrupt
handler, when a change of privilege level occurs.
5.12
COMBINING PAGE AND SEGMENT PROTECTION
When paging is enabled, the processor evaluates segment protection first, then evaluates page protection. If the
processor detects a protection violation at either the segment level or the page level, the memory access is not
carried out and an exception is generated. If an exception is generated by segmentation, no paging exception is
generated.
Page-level protections cannot be used to override segment-level protection. For example, a code segment is by
definition not writable. If a code segment is paged, setting the R/W flag for the pages to read-write does not make
the pages writable. Attempts to write into the pages will be blocked by segment-level protection checks.
Page-level protection can be used to enhance segment-level protection. For example, if a large read-write data
segment is paged, the page-protection mechanism can be used to write-protect individual pages.
Table 5-3. Combined Page-Directory and Page-Table Protection
Page-Directory Entry
Page-Table Entry
Combined Effect
Privilege
Access Type
Privilege
Access Type
Privilege
Access Type
User
Read-Only
User
Read-Only
User
Read-Only
User
Read-Only
User
Read-Write
User
Read-Only
User
Read-Write
User
Read-Only
User
Read-Only
User
Read-Write
User
Read-Write
User
Read/Write
User
Read-Only
Supervisor
Read-Only
Supervisor
Read/Write*
User
Read-Only
Supervisor
Read-Write
Supervisor
Read/Write*
User
Read-Write
Supervisor
Read-Only
Supervisor
Read/Write*
User
Read-Write
Supervisor
Read-Write
Supervisor
Read/Write
Supervisor
Read-Only
User
Read-Only
Supervisor
Read/Write*
Supervisor
Read-Only
User
Read-Write
Supervisor
Read/Write*
Supervisor
Read-Write
User
Read-Only
Supervisor
Read/Write*
Supervisor
Read-Write
User
Read-Write
Supervisor
Read/Write
Supervisor
Read-Only
Supervisor
Read-Only
Supervisor
Read/Write*
Supervisor
Read-Only
Supervisor
Read-Write
Supervisor
Read/Write*
Supervisor
Read-Write
Supervisor
Read-Only
Supervisor
Read/Write*
Supervisor
Read-Write
Supervisor
Read-Write
Supervisor
Read/Write
NOTE:
* If CR0.WP = 1, access type is determined by the R/W flags of the page-directory and page-table entries. IF CR0.WP = 0, supervisor
privilege permits read-write access.
Vol. 3A 5-29
PROTECTION
5.13
PAGE-LEVEL PROTECTION AND EXECUTE-DISABLE BIT
In addition to page-level protection offered by the U/S and R/W flags, paging structures used with PAE paging and
IA-32e paging (see Chapter 4) provide the execute-disable bit. This bit offers additional protection for data pages.
An Intel 64 or IA-32 processor with the execute-disable bit capability can prevent data pages from being used by
malicious software to execute code. This capability is provided in:
•
•
32-bit protected mode with PAE enabled.
IA-32e mode.
While the execute-disable bit capability does not introduce new instructions, it does require operating systems to
use a PAE-enabled environment and establish a page-granular protection policy for memory pages.
If the execute-disable bit of a memory page is set, that page can be used only as data. An attempt to execute code
from a memory page with the execute-disable bit set causes a page-fault exception.
The execute-disable capability is supported only with PAE paging and IA-32e paging. It is not supported with 32-bit
paging. Existing page-level protection mechanisms (see Section 5.11, “Page-Level Protection”) continue to apply
to memory pages independent of the execute-disable setting.
5.13.1
Detecting and Enabling the Execute-Disable Capability
Software can detect the presence of the execute-disable capability using the CPUID instruction.
CPUID.80000001H:EDX.NX [bit 20] = 1 indicates the capability is available.
If the capability is available, software can enable it by setting IA32_EFER.NXE[bit 11] to 1. IA32_EFER is available
if CPUID.80000001H.EDX[bit 20 or 29] = 1.
If the execute-disable capability is not available, a write to set IA32_EFER.NXE produces a #GP exception. See
Table 5-4.
Table 5-4. Extended Feature Enable MSR (IA32_EFER)
63:12
11
10
9
8
7:1
0
Reserved
Execute-disable bit
enable (NXE)
IA-32e mode
active (LMA)
Reserved
IA-32e mode
enable (LME)
Reserved
SysCall enable (SCE)
5.13.2
Execute-Disable Page Protection
The execute-disable bit in the paging structures enhances page protection for data pages. Instructions cannot be
fetched from a memory page if IA32_EFER.NXE =1 and the execute-disable bit is set in any of the paging-structure
entries used to map the page. Table 5-5 lists the valid usage of a page in relation to the value of execute-disable bit
(bit 63) of the corresponding entry in each level of the paging structures. Execute-disable protection can be activated using the execute-disable bit at any level of the paging structure, irrespective of the corresponding entry in
other levels. When execute-disable protection is not activated, the page can be used as code or data.
5-30 Vol. 3A
PROTECTION
Table 5-5. IA-32e Mode Page Level Protection Matrix
with Execute-Disable Bit Capability
Execute Disable Bit Value (Bit 63)
Valid Usage
PML4
PDP
PDE
PTE
Bit 63 = 1
*
*
*
Data
*
Bit 63 = 1
*
*
Data
*
*
Bit 63 = 1
*
Data
*
*
*
Bit 63 = 1
Data
Bit 63 = 0
Bit 63 = 0
Bit 63 = 0
Bit 63 = 0
Data/Code
NOTES:
* Value not checked.
In legacy PAE-enabled mode, Table 5-6 and Table 5-7 show the effect of setting the execute-disable bit for code
and data pages.
Table 5-6. Legacy PAE-Enabled 4-KByte Page Level Protection Matrix
with Execute-Disable Bit Capability
Execute Disable Bit Value (Bit 63)
Valid Usage
PDE
PTE
Bit 63 = 1
*
Data
*
Bit 63 = 1
Data
Bit 63 = 0
Bit 63 = 0
Data/Code
NOTE:
* Value not checked.
Table 5-7. Legacy PAE-Enabled 2-MByte Page Level Protection
with Execute-Disable Bit Capability
Execute Disable Bit Value (Bit 63)
Valid Usage
PDE
Bit 63 = 1
Data
Bit 63 = 0
Data/Code
5.13.3
Reserved Bit Checking
The processor enforces reserved bit checking in paging data structure entries. The bits being checked varies with
paging mode and may vary with the size of physical address space.
Table 5-8 shows the reserved bits that are checked when the execute disable bit capability is enabled (CR4.PAE = 1
and IA32_EFER.NXE = 1). Table 5-8 and Table 5-9 show the following paging modes:
•
•
•
Non-PAE 4-KByte paging: 4-KByte-page only paging (CR4.PAE = 0, CR4.PSE = 0).
PSE36: 4-KByte and 4-MByte pages (CR4.PAE = 0, CR4.PSE = 1).
PAE: 4-KByte and 2-MByte pages (CR4.PAE = 1, CR4.PSE = X).
The reserved bit checking depends on the physical address size supported by the implementation, which is
reported in CPUID.80000008H. See the table note.
Vol. 3A 5-31
PROTECTION
Table 5-8. IA-32e Mode Page Level Protection Matrix with Execute-Disable Bit Capability Enabled
Mode
Paging Mode
Check Bits
32-bit
4-KByte paging (non-PAE)
No reserved bits checked
64-bit
PSE36 - PDE, 4-MByte page
Bit [21]
PSE36 - PDE, 4-KByte page
No reserved bits checked
PSE36 - PTE
No reserved bits checked
PAE - PDP table entry
Bits [63:MAXPHYADDR] & [8:5] & [2:1] *
PAE - PDE, 2-MByte page
Bits [62:MAXPHYADDR] & [20:13] *
PAE - PDE, 4-KByte page
Bits [62:MAXPHYADDR] *
PAE - PTE
Bits [62:MAXPHYADDR] *
PML4E
Bits [51:MAXPHYADDR] *
PDPTE
Bits [51:MAXPHYADDR] *
PDE, 2-MByte page
Bits [51:MAXPHYADDR] & [20:13] *
PDE, 4-KByte page
Bits [51:MAXPHYADDR] *
PTE
Bits [51:MAXPHYADDR] *
NOTES:
* MAXPHYADDR is the maximum physical address size and is indicated by CPUID.80000008H:EAX[bits 7-0].
If execute disable bit capability is not enabled or not available, reserved bit checking in 64-bit mode includes bit 63
and additional bits. This and reserved bit checking for legacy 32-bit paging modes are shown in Table 5-10.
Table 5-9. Reserved Bit Checking WIth Execute-Disable Bit Capability Not Enabled
Mode
Paging Mode
Check Bits
32-bit
KByte paging (non-PAE)
No reserved bits checked
PSE36 - PDE, 4-MByte page
Bit [21]
PSE36 - PDE, 4-KByte page
No reserved bits checked
PSE36 - PTE
No reserved bits checked
PAE - PDP table entry
Bits [63:MAXPHYADDR] & [8:5] & [2:1]*
PAE - PDE, 2-MByte page
Bits [63:MAXPHYADDR] & [20:13]*
PAE - PDE, 4-KByte page
Bits [63:MAXPHYADDR]*
PAE - PTE
Bits [63:MAXPHYADDR]*
PML4E
Bit [63], bits [51:MAXPHYADDR]*
64-bit
PDPTE
Bit [63], bits [51:MAXPHYADDR]*
PDE, 2-MByte page
Bit [63], bits [51:MAXPHYADDR] & [20:13]*
PDE, 4-KByte page
Bit [63], bits [51:MAXPHYADDR]*
PTE
Bit [63], bits [51:MAXPHYADDR]*
NOTES:
* MAXPHYADDR is the maximum physical address size and is indicated by CPUID.80000008H:EAX[bits 7-0].
5.13.4
Exception Handling
When execute disable bit capability is enabled (IA32_EFER.NXE = 1), conditions for a page fault to occur include
the same conditions that apply to an Intel 64 or IA-32 processor without execute disable bit capability plus the
following new condition: an instruction fetch to a linear address that translates to physical address in a memory
page that has the execute-disable bit set.
5-32 Vol. 3A
PROTECTION
An Execute Disable Bit page fault can occur at all privilege levels. It can occur on any instruction fetch, including
(but not limited to): near branches, far branches, CALL/RET/INT/IRET execution, sequential instruction fetches,
and task switches. The execute-disable bit in the page translation mechanism is checked only when:
•
•
IA32_EFER.NXE = 1.
The instruction translation look-aside buffer (ITLB) is loaded with a page that is not already present in the ITLB.
Vol. 3A 5-33
PROTECTION
5-34 Vol. 3A
CHAPTER 6
INTERRUPT AND EXCEPTION HANDLING
This chapter describes the interrupt and exception-handling mechanism when operating in protected mode on an
Intel 64 or IA-32 processor. Most of the information provided here also applies to interrupt and exception mechanisms used in real-address, virtual-8086 mode, and 64-bit mode.
Chapter 20, “8086 Emulation,” describes information specific to interrupt and exception mechanisms in realaddress and virtual-8086 mode. Section 6.14, “Exception and Interrupt Handling in 64-bit Mode,” describes information specific to interrupt and exception mechanisms in IA-32e mode and 64-bit sub-mode.
6.1
INTERRUPT AND EXCEPTION OVERVIEW
Interrupts and exceptions are events that indicate that a condition exists somewhere in the system, the processor,
or within the currently executing program or task that requires the attention of a processor. They typically result in
a forced transfer of execution from the currently running program or task to a special software routine or task
called an interrupt handler or an exception handler. The action taken by a processor in response to an interrupt or
exception is referred to as servicing or handling the interrupt or exception.
Interrupts occur at random times during the execution of a program, in response to signals from hardware. System
hardware uses interrupts to handle events external to the processor, such as requests to service peripheral devices.
Software can also generate interrupts by executing the INT n instruction.
Exceptions occur when the processor detects an error condition while executing an instruction, such as division by
zero. The processor detects a variety of error conditions including protection violations, page faults, and internal
machine faults. The machine-check architecture of the Pentium 4, Intel Xeon, P6 family, and Pentium processors
also permits a machine-check exception to be generated when internal hardware errors and bus errors are
detected.
When an interrupt is received or an exception is detected, the currently running procedure or task is suspended
while the processor executes an interrupt or exception handler. When execution of the handler is complete, the
processor resumes execution of the interrupted procedure or task. The resumption of the interrupted procedure or
task happens without loss of program continuity, unless recovery from an exception was not possible or an interrupt caused the currently running program to be terminated.
This chapter describes the processor’s interrupt and exception-handling mechanism, when operating in protected
mode. A description of the exceptions and the conditions that cause them to be generated is given at the end of this
chapter.
6.2
EXCEPTION AND INTERRUPT VECTORS
To aid in handling exceptions and interrupts, each architecturally defined exception and each interrupt condition
requiring special handling by the processor is assigned a unique identification number, called a vector number. The
processor uses the vector number assigned to an exception or interrupt as an index into the interrupt descriptor
table (IDT). The table provides the entry point to an exception or interrupt handler (see Section 6.10, “Interrupt
Descriptor Table (IDT)”).
The allowable range for vector numbers is 0 to 255. Vector numbers in the range 0 through 31 are reserved by the
Intel 64 and IA-32 architectures for architecture-defined exceptions and interrupts. Not all of the vector numbers
in this range have a currently defined function. The unassigned vector numbers in this range are reserved. Do not
use the reserved vector numbers.
Vector numbers in the range 32 to 255 are designated as user-defined interrupts and are not reserved by the Intel
64 and IA-32 architecture. These interrupts are generally assigned to external I/O devices to enable those devices
to send interrupts to the processor through one of the external hardware interrupt mechanisms (see Section 6.3,
“Sources of Interrupts”).
Vol. 3A 6-1
INTERRUPT AND EXCEPTION HANDLING
Table 6-1 shows vector number assignments for architecturally defined exceptions and for the NMI interrupt. This
table gives the exception type (see Section 6.5, “Exception Classifications”) and indicates whether an error code is
saved on the stack for the exception. The source of each predefined exception and the NMI interrupt is also given.
6.3
SOURCES OF INTERRUPTS
The processor receives interrupts from two sources:
•
•
External (hardware generated) interrupts.
Software-generated interrupts.
6.3.1
External Interrupts
External interrupts are received through pins on the processor or through the local APIC. The primary interrupt pins
on Pentium 4, Intel Xeon, P6 family, and Pentium processors are the LINT[1:0] pins, which are connected to the
local APIC (see Chapter 10, “Advanced Programmable Interrupt Controller (APIC)”). When the local APIC is
enabled, the LINT[1:0] pins can be programmed through the APIC’s local vector table (LVT) to be associated with
any of the processor’s exception or interrupt vectors.
When the local APIC is global/hardware disabled, these pins are configured as INTR and NMI pins, respectively.
Asserting the INTR pin signals the processor that an external interrupt has occurred. The processor reads from the
system bus the interrupt vector number provided by an external interrupt controller, such as an 8259A (see Section
6.2, “Exception and Interrupt Vectors”). Asserting the NMI pin signals a non-maskable interrupt (NMI), which is
assigned to interrupt vector 2.
Table 6-1. Protected-Mode Exceptions and Interrupts
Vector
No.
Mnemonic
Description
Type
Error
Code
Source
0
#DE
Divide Error
Fault
No
DIV and IDIV instructions.
1
#DB
RESERVED
Fault/ Trap
No
For Intel use only.
2
—
NMI Interrupt
Interrupt
No
Nonmaskable external interrupt.
3
#BP
Breakpoint
Trap
No
INT 3 instruction.
4
#OF
Overflow
Trap
No
INTO instruction.
5
#BR
BOUND Range Exceeded
Fault
No
BOUND instruction.
6
#UD
Invalid Opcode (Undefined Opcode)
Fault
No
UD2 instruction or reserved opcode.1
7
#NM
Device Not Available (No Math
Coprocessor)
Fault
No
Floating-point or WAIT/FWAIT instruction.
8
#DF
Double Fault
Abort
Yes
(zero)
Any instruction that can generate an
exception, an NMI, or an INTR.
Coprocessor Segment Overrun
(reserved)
Fault
No
Floating-point instruction.2
9
10
#TS
Invalid TSS
Fault
Yes
Task switch or TSS access.
11
#NP
Segment Not Present
Fault
Yes
Loading segment registers or accessing
system segments.
12
#SS
Stack-Segment Fault
Fault
Yes
Stack operations and SS register loads.
13
#GP
General Protection
Fault
Yes
Any memory reference and other
protection checks.
14
#PF
Page Fault
Fault
Yes
Any memory reference.
15
—
(Intel reserved. Do not use.)
6-2 Vol. 3A
No
INTERRUPT AND EXCEPTION HANDLING
Table 6-1. Protected-Mode Exceptions and Interrupts (Contd.)
16
#MF
x87 FPU Floating-Point Error (Math
Fault)
Fault
No
x87 FPU floating-point or WAIT/FWAIT
instruction.
17
#AC
Alignment Check
Fault
Yes
(Zero)
Any data reference in memory.3
18
#MC
Machine Check
Abort
No
Error codes (if any) and source are model
dependent.4
19
#XM
SIMD Floating-Point Exception
Fault
No
SSE/SSE2/SSE3 floating-point
instructions5
20
#VE
Virtualization Exception
Fault
No
EPT violations6
21-31
—
Intel reserved. Do not use.
32-255
—
User Defined (Non-reserved)
Interrupts
Interrupt
External interrupt or INT n instruction.
NOTES:
1. The UD2 instruction was introduced in the Pentium Pro processor.
2. Processors after the Intel386 processor do not generate this exception.
3. This exception was introduced in the Intel486 processor.
4. This exception was introduced in the Pentium processor and enhanced in the P6 family processors.
5. This exception was introduced in the Pentium III processor.
6. This exception can occur only on processors that support the 1-setting of the “EPT-violation #VE” VM-execution control.
The processor’s local APIC is normally connected to a system-based I/O APIC. Here, external interrupts received at
the I/O APIC’s pins can be directed to the local APIC through the system bus (Pentium 4, Intel Core Duo, Intel Core
2, Intel® Atom™, and Intel Xeon processors) or the APIC serial bus (P6 family and Pentium processors). The I/O
APIC determines the vector number of the interrupt and sends this number to the local APIC. When a system
contains multiple processors, processors can also send interrupts to one another by means of the system bus
(Pentium 4, Intel Core Duo, Intel Core 2, Intel Atom, and Intel Xeon processors) or the APIC serial bus (P6 family
and Pentium processors).
The LINT[1:0] pins are not available on the Intel486 processor and earlier Pentium processors that do not contain
an on-chip local APIC. These processors have dedicated NMI and INTR pins. With these processors, external interrupts are typically generated by a system-based interrupt controller (8259A), with the interrupts being signaled
through the INTR pin.
Note that several other pins on the processor can cause a processor interrupt to occur. However, these interrupts
are not handled by the interrupt and exception mechanism described in this chapter. These pins include the
RESET#, FLUSH#, STPCLK#, SMI#, R/S#, and INIT# pins. Whether they are included on a particular processor is
implementation dependent. Pin functions are described in the data books for the individual processors. The SMI#
pin is described in Chapter 34, “System Management Mode.”
6.3.2
Maskable Hardware Interrupts
Any external interrupt that is delivered to the processor by means of the INTR pin or through the local APIC is called
a maskable hardware interrupt. Maskable hardware interrupts that can be delivered through the INTR pin include
all IA-32 architecture defined interrupt vectors from 0 through 255; those that can be delivered through the local
APIC include interrupt vectors 16 through 255.
The IF flag in the EFLAGS register permits all maskable hardware interrupts to be masked as a group (see Section
6.8.1, “Masking Maskable Hardware Interrupts”). Note that when interrupts 0 through 15 are delivered through the
local APIC, the APIC indicates the receipt of an illegal vector.
Vol. 3A 6-3
INTERRUPT AND EXCEPTION HANDLING
6.3.3
Software-Generated Interrupts
The INT n instruction permits interrupts to be generated from within software by supplying an interrupt vector
number as an operand. For example, the INT 35 instruction forces an implicit call to the interrupt handler for interrupt 35.
Any of the interrupt vectors from 0 to 255 can be used as a parameter in this instruction. If the processor’s
predefined NMI vector is used, however, the response of the processor will not be the same as it would be from an
NMI interrupt generated in the normal manner. If vector number 2 (the NMI vector) is used in this instruction, the
NMI interrupt handler is called, but the processor’s NMI-handling hardware is not activated.
Interrupts generated in software with the INT n instruction cannot be masked by the IF flag in the EFLAGS register.
6.4
SOURCES OF EXCEPTIONS
The processor receives exceptions from three sources:
•
•
•
Processor-detected program-error exceptions.
Software-generated exceptions.
Machine-check exceptions.
6.4.1
Program-Error Exceptions
The processor generates one or more exceptions when it detects program errors during the execution in an application program or the operating system or executive. Intel 64 and IA-32 architectures define a vector number for
each processor-detectable exception. Exceptions are classified as faults, traps, and aborts (see Section 6.5,
“Exception Classifications”).
6.4.2
Software-Generated Exceptions
The INTO, INT 3, and BOUND instructions permit exceptions to be generated in software. These instructions allow
checks for exception conditions to be performed at points in the instruction stream. For example, INT 3 causes a
breakpoint exception to be generated.
The INT n instruction can be used to emulate exceptions in software; but there is a limitation. If INT n provides a
vector for one of the architecturally-defined exceptions, the processor generates an interrupt to the correct vector
(to access the exception handler) but does not push an error code on the stack. This is true even if the associated
hardware-generated exception normally produces an error code. The exception handler will still attempt to pop an
error code from the stack while handling the exception. Because no error code was pushed, the handler will pop off
and discard the EIP instead (in place of the missing error code). This sends the return to the wrong location.
6.4.3
Machine-Check Exceptions
The P6 family and Pentium processors provide both internal and external machine-check mechanisms for checking
the operation of the internal chip hardware and bus transactions. These mechanisms are implementation dependent. When a machine-check error is detected, the processor signals a machine-check exception (vector 18) and
returns an error code.
See Chapter 6, “Interrupt 18—Machine-Check Exception (#MC)” and Chapter 15, “Machine-Check Architecture,”
for more information about the machine-check mechanism.
6.5
EXCEPTION CLASSIFICATIONS
Exceptions are classified as faults, traps, or aborts depending on the way they are reported and whether the
instruction that caused the exception can be restarted without loss of program or task continuity.
6-4 Vol. 3A
INTERRUPT AND EXCEPTION HANDLING
•
Faults — A fault is an exception that can generally be corrected and that, once corrected, allows the program
to be restarted with no loss of continuity. When a fault is reported, the processor restores the machine state to
the state prior to the beginning of execution of the faulting instruction. The return address (saved contents of
the CS and EIP registers) for the fault handler points to the faulting instruction, rather than to the instruction
following the faulting instruction.
•
Traps — A trap is an exception that is reported immediately following the execution of the trapping instruction.
Traps allow execution of a program or task to be continued without loss of program continuity. The return
address for the trap handler points to the instruction to be executed after the trapping instruction.
•
Aborts — An abort is an exception that does not always report the precise location of the instruction causing
the exception and does not allow a restart of the program or task that caused the exception. Aborts are used
to report severe errors, such as hardware errors and inconsistent or illegal values in system tables.
NOTE
One exception subset normally reported as a fault is not restartable. Such exceptions result in loss
of some processor state. For example, executing a POPAD instruction where the stack frame
crosses over the end of the stack segment causes a fault to be reported. In this situation, the
exception handler sees that the instruction pointer (CS:EIP) has been restored as if the POPAD
instruction had not been executed. However, internal processor state (the general-purpose
registers) will have been modified. Such cases are considered programming errors. An application
causing this class of exceptions should be terminated by the operating system.
6.6
PROGRAM OR TASK RESTART
To allow the restarting of program or task following the handling of an exception or an interrupt, all exceptions
(except aborts) are guaranteed to report exceptions on an instruction boundary. All interrupts are guaranteed to be
taken on an instruction boundary.
For fault-class exceptions, the return instruction pointer (saved when the processor generates an exception) points
to the faulting instruction. So, when a program or task is restarted following the handling of a fault, the faulting
instruction is restarted (re-executed). Restarting the faulting instruction is commonly used to handle exceptions
that are generated when access to an operand is blocked. The most common example of this type of fault is a pagefault exception (#PF) that occurs when a program or task references an operand located on a page that is not in
memory. When a page-fault exception occurs, the exception handler can load the page into memory and resume
execution of the program or task by restarting the faulting instruction. To insure that the restart is handled transparently to the currently executing program or task, the processor saves the necessary registers and stack pointers
to allow a restart to the state prior to the execution of the faulting instruction.
For trap-class exceptions, the return instruction pointer points to the instruction following the trapping instruction.
If a trap is detected during an instruction which transfers execution, the return instruction pointer reflects the
transfer. For example, if a trap is detected while executing a JMP instruction, the return instruction pointer points
to the destination of the JMP instruction, not to the next address past the JMP instruction. All trap exceptions allow
program or task restart with no loss of continuity. For example, the overflow exception is a trap exception. Here,
the return instruction pointer points to the instruction following the INTO instruction that tested EFLAGS.OF (overflow) flag. The trap handler for this exception resolves the overflow condition. Upon return from the trap handler,
program or task execution continues at the instruction following the INTO instruction.
The abort-class exceptions do not support reliable restarting of the program or task. Abort handlers are designed
to collect diagnostic information about the state of the processor when the abort exception occurred and then shut
down the application and system as gracefully as possible.
Interrupts rigorously support restarting of interrupted programs and tasks without loss of continuity. The return
instruction pointer saved for an interrupt points to the next instruction to be executed at the instruction boundary
where the processor took the interrupt. If the instruction just executed has a repeat prefix, the interrupt is taken
at the end of the current iteration with the registers set to execute the next iteration.
The ability of a P6 family processor to speculatively execute instructions does not affect the taking of interrupts by
the processor. Interrupts are taken at instruction boundaries located during the retirement phase of instruction
execution; so they are always taken in the “in-order” instruction stream. See Chapter 2, “Intel® 64 and IA-32
Vol. 3A 6-5
INTERRUPT AND EXCEPTION HANDLING
Architectures,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, for more information about the P6 family processors’ microarchitecture and its support for out-of-order instruction execution.
Note that the Pentium processor and earlier IA-32 processors also perform varying amounts of prefetching and
preliminary decoding. With these processors as well, exceptions and interrupts are not signaled until actual “inorder” execution of the instructions. For a given code sample, the signaling of exceptions occurs uniformly when
the code is executed on any family of IA-32 processors (except where new exceptions or new opcodes have been
defined).
6.7
NONMASKABLE INTERRUPT (NMI)
The nonmaskable interrupt (NMI) can be generated in either of two ways:
•
•
External hardware asserts the NMI pin.
The processor receives a message on the system bus (Pentium 4, Intel Core Duo, Intel Core 2, Intel Atom, and
Intel Xeon processors) or the APIC serial bus (P6 family and Pentium processors) with a delivery mode NMI.
When the processor receives a NMI from either of these sources, the processor handles it immediately by calling
the NMI handler pointed to by interrupt vector number 2. The processor also invokes certain hardware conditions
to insure that no other interrupts, including NMI interrupts, are received until the NMI handler has completed
executing (see Section 6.7.1, “Handling Multiple NMIs”).
Also, when an NMI is received from either of the above sources, it cannot be masked by the IF flag in the EFLAGS
register.
It is possible to issue a maskable hardware interrupt (through the INTR pin) to vector 2 to invoke the NMI interrupt
handler; however, this interrupt will not truly be an NMI interrupt. A true NMI interrupt that activates the
processor’s NMI-handling hardware can only be delivered through one of the mechanisms listed above.
6.7.1
Handling Multiple NMIs
While an NMI interrupt handler is executing, the processor blocks delivery of subsequent NMIs until the next execution of the IRET instruction. This blocking of NMIs prevents nested execution of the NMI handler. It is recommended
that the NMI interrupt handler be accessed through an interrupt gate to disable maskable hardware interrupts (see
Section 6.8.1, “Masking Maskable Hardware Interrupts”).
An execution of the IRET instruction unblocks NMIs even if the instruction causes a fault. For example, if the IRET
instruction executes with EFLAGS.VM = 1 and IOPL of less than 3, a general-protection exception is generated (see
Section 20.2.7, “Sensitive Instructions”). In such a case, NMIs are unmasked before the exception handler is
invoked.
6.8
ENABLING AND DISABLING INTERRUPTS
The processor inhibits the generation of some interrupts, depending on the state of the processor and of the IF and
RF flags in the EFLAGS register, as described in the following sections.
6.8.1
Masking Maskable Hardware Interrupts
The IF flag can disable the servicing of maskable hardware interrupts received on the processor’s INTR pin or
through the local APIC (see Section 6.3.2, “Maskable Hardware Interrupts”). When the IF flag is clear, the
processor inhibits interrupts delivered to the INTR pin or through the local APIC from generating an internal interrupt request; when the IF flag is set, interrupts delivered to the INTR or through the local APIC pin are processed
as normal external interrupts.
The IF flag does not affect non-maskable interrupts (NMIs) delivered to the NMI pin or delivery mode NMI
messages delivered through the local APIC, nor does it affect processor generated exceptions. As with the other
flags in the EFLAGS register, the processor clears the IF flag in response to a hardware reset.
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INTERRUPT AND EXCEPTION HANDLING
The fact that the group of maskable hardware interrupts includes the reserved interrupt and exception vectors 0
through 32 can potentially cause confusion. Architecturally, when the IF flag is set, an interrupt for any of the
vectors from 0 through 32 can be delivered to the processor through the INTR pin and any of the vectors from 16
through 32 can be delivered through the local APIC. The processor will then generate an interrupt and call the
interrupt or exception handler pointed to by the vector number. So for example, it is possible to invoke the pagefault handler through the INTR pin (by means of vector 14); however, this is not a true page-fault exception. It is
an interrupt. As with the INT n instruction (see Section 6.4.2, “Software-Generated Exceptions”), when an interrupt is generated through the INTR pin to an exception vector, the processor does not push an error code on the
stack, so the exception handler may not operate correctly.
The IF flag can be set or cleared with the STI (set interrupt-enable flag) and CLI (clear interrupt-enable flag)
instructions, respectively. These instructions may be executed only if the CPL is equal to or less than the IOPL. A
general-protection exception (#GP) is generated if they are executed when the CPL is greater than the IOPL. (The
effect of the IOPL on these instructions is modified slightly when the virtual mode extension is enabled by setting
the VME flag in control register CR4: see Section 20.3, “Interrupt and Exception Handling in Virtual-8086 Mode.”
Behavior is also impacted by the PVI flag: see Section 20.4, “Protected-Mode Virtual Interrupts.”
The IF flag is also affected by the following operations:
•
The PUSHF instruction stores all flags on the stack, where they can be examined and modified. The POPF
instruction can be used to load the modified flags back into the EFLAGS register.
•
Task switches and the POPF and IRET instructions load the EFLAGS register; therefore, they can be used to
modify the setting of the IF flag.
•
When an interrupt is handled through an interrupt gate, the IF flag is automatically cleared, which disables
maskable hardware interrupts. (If an interrupt is handled through a trap gate, the IF flag is not cleared.)
See the descriptions of the CLI, STI, PUSHF, POPF, and IRET instructions in Chapter 3, “Instruction Set Reference,
A-L,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A, and Chapter 4, “Instruction Set Reference, M-Z,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2B, for a
detailed description of the operations these instructions are allowed to perform on the IF flag.
6.8.2
Masking Instruction Breakpoints
The RF (resume) flag in the EFLAGS register controls the response of the processor to instruction-breakpoint conditions (see the description of the RF flag in Section 2.3, “System Flags and Fields in the EFLAGS Register”).
When set, it prevents an instruction breakpoint from generating a debug exception (#DB); when clear, instruction
breakpoints will generate debug exceptions. The primary function of the RF flag is to prevent the processor from
going into a debug exception loop on an instruction-breakpoint. See Section 17.3.1.1, “Instruction-Breakpoint
Exception Condition,” for more information on the use of this flag.
6.8.3
Masking Exceptions and Interrupts When Switching Stacks
To switch to a different stack segment, software often uses a pair of instructions, for example:
MOV SS, AX
MOV ESP, StackTop
If an interrupt or exception occurs after the segment selector has been loaded into the SS register but before the
ESP register has been loaded, these two parts of the logical address into the stack space are inconsistent for the
duration of the interrupt or exception handler.
To prevent this situation, the processor inhibits interrupts, debug exceptions, and single-step trap exceptions after
either a MOV to SS instruction or a POP to SS instruction, until the instruction boundary following the next instruction is reached. All other faults may still be generated. If the LSS instruction is used to modify the contents of the
SS register (which is the recommended method of modifying this register), this problem does not occur.
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INTERRUPT AND EXCEPTION HANDLING
6.9
PRIORITY AMONG SIMULTANEOUS EXCEPTIONS AND INTERRUPTS
If more than one exception or interrupt is pending at an instruction boundary, the processor services them in a
predictable order. Table 6-2 shows the priority among classes of exception and interrupt sources.
Table 6-2. Priority Among Simultaneous Exceptions and Interrupts
Priority
1 (Highest)
Description
Hardware Reset and Machine Checks
- RESET
- Machine Check
2
Trap on Task Switch
- T flag in TSS is set
3
External Hardware Interventions
- FLUSH
- STOPCLK
- SMI
- INIT
4
Traps on the Previous Instruction
- Breakpoints
- Debug Trap Exceptions (TF flag set or data/I-O breakpoint)
5
Nonmaskable Interrupts (NMI) 1
6
Maskable Hardware Interrupts 1
7
Code Breakpoint Fault
8
Faults from Fetching Next Instruction
- Code-Segment Limit Violation
- Code Page Fault
9
Faults from Decoding the Next Instruction
- Instruction length > 15 bytes
- Invalid Opcode
- Coprocessor Not Available
10 (Lowest)
Faults on Executing an Instruction
- Overflow
- Bound error
- Invalid TSS
- Segment Not Present
- Stack fault
- General Protection
- Data Page Fault
- Alignment Check
- x87 FPU Floating-point exception
- SIMD floating-point exception
- Virtualization exception
NOTE
1. The Intel® 486 processor and earlier processors group nonmaskable and maskable interrupts in the same priority class.
While priority among these classes listed in Table 6-2 is consistent throughout the architecture, exceptions within
each class are implementation-dependent and may vary from processor to processor. The processor first services
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INTERRUPT AND EXCEPTION HANDLING
a pending exception or interrupt from the class which has the highest priority, transferring execution to the first
instruction of the handler. Lower priority exceptions are discarded; lower priority interrupts are held pending.
Discarded exceptions are re-generated when the interrupt handler returns execution to the point in the program or
task where the exceptions and/or interrupts occurred.
6.10
INTERRUPT DESCRIPTOR TABLE (IDT)
The interrupt descriptor table (IDT) associates each exception or interrupt vector with a gate descriptor for the
procedure or task used to service the associated exception or interrupt. Like the GDT and LDTs, the IDT is an array
of 8-byte descriptors (in protected mode). Unlike the GDT, the first entry of the IDT may contain a descriptor. To
form an index into the IDT, the processor scales the exception or interrupt vector by eight (the number of bytes in
a gate descriptor). Because there are only 256 interrupt or exception vectors, the IDT need not contain more than
256 descriptors. It can contain fewer than 256 descriptors, because descriptors are required only for the interrupt
and exception vectors that may occur. All empty descriptor slots in the IDT should have the present flag for the
descriptor set to 0.
The base addresses of the IDT should be aligned on an 8-byte boundary to maximize performance of cache line
fills. The limit value is expressed in bytes and is added to the base address to get the address of the last valid byte.
A limit value of 0 results in exactly 1 valid byte. Because IDT entries are always eight bytes long, the limit should
always be one less than an integral multiple of eight (that is, 8N – 1).
The IDT may reside anywhere in the linear address space. As shown in Figure 6-1, the processor locates the IDT
using the IDTR register. This register holds both a 32-bit base address and 16-bit limit for the IDT.
The LIDT (load IDT register) and SIDT (store IDT register) instructions load and store the contents of the IDTR
register, respectively. The LIDT instruction loads the IDTR register with the base address and limit held in a
memory operand. This instruction can be executed only when the CPL is 0. It normally is used by the initialization
code of an operating system when creating an IDT. An operating system also may use it to change from one IDT to
another. The SIDT instruction copies the base and limit value stored in IDTR to memory. This instruction can be
executed at any privilege level.
If a vector references a descriptor beyond the limit of the IDT, a general-protection exception (#GP) is generated.
NOTE
Because interrupts are delivered to the processor core only once, an incorrectly configured IDT
could result in incomplete interrupt handling and/or the blocking of interrupt delivery.
IA-32 architecture rules need to be followed for setting up IDTR base/limit/access fields and each
field in the gate descriptors. The same apply for the Intel 64 architecture. This includes implicit
referencing of the destination code segment through the GDT or LDT and accessing the stack.
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INTERRUPT AND EXCEPTION HANDLING
IDTR Register
47
16 15
IDT Base Address
0
IDT Limit
+
Interrupt
Descriptor Table (IDT)
Gate for
Interrupt #n
(n−1)∗8
Gate for
Interrupt #3
16
Gate for
Interrupt #2
8
Gate for
Interrupt #1
31
0
0
Figure 6-1. Relationship of the IDTR and IDT
6.11
IDT DESCRIPTORS
The IDT may contain any of three kinds of gate descriptors:
•
•
•
Task-gate descriptor
Interrupt-gate descriptor
Trap-gate descriptor
Figure 6-2 shows the formats for the task-gate, interrupt-gate, and trap-gate descriptors. The format of a task
gate used in an IDT is the same as that of a task gate used in the GDT or an LDT (see Section 7.2.5, “Task-Gate
Descriptor”). The task gate contains the segment selector for a TSS for an exception and/or interrupt handler task.
Interrupt and trap gates are very similar to call gates (see Section 5.8.3, “Call Gates”). They contain a far pointer
(segment selector and offset) that the processor uses to transfer program execution to a handler procedure in an
exception- or interrupt-handler code segment. These gates differ in the way the processor handles the IF flag in the
EFLAGS register (see Section 6.12.1.2, “Flag Usage By Exception- or Interrupt-Handler Procedure”).
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INTERRUPT AND EXCEPTION HANDLING
Task Gate
31
16 15 14 13 12
P
31
D
P
L
0
8 7
4
0 0 1 0 1
16 15
0
TSS Segment Selector
0
Interrupt Gate
31
16 15 14 13 12
Offset 31..16
31
P
D
P
L
8 7
0 D 1 1 0
5 4
0
0 0 0
16 15
4
0
Segment Selector
Offset 15..0
0
Trap Gate
31
16 15 14 13 12
Offset 31..16
31
P
D
P
L
8 7
0 D 1 1 1
5 4
0 0 0
16 15
Segment Selector
DPL
Offset
P
Selector
D
0
4
0
Offset 15..0
0
Descriptor Privilege Level
Offset to procedure entry point
Segment Present flag
Segment Selector for destination code segment
Size of gate: 1 = 32 bits; 0 = 16 bits
Reserved
Figure 6-2. IDT Gate Descriptors
6.12
EXCEPTION AND INTERRUPT HANDLING
The processor handles calls to exception- and interrupt-handlers similar to the way it handles calls with a CALL
instruction to a procedure or a task. When responding to an exception or interrupt, the processor uses the exception or interrupt vector as an index to a descriptor in the IDT. If the index points to an interrupt gate or trap gate,
the processor calls the exception or interrupt handler in a manner similar to a CALL to a call gate (see Section
5.8.2, “Gate Descriptors,” through Section 5.8.6, “Returning from a Called Procedure”). If index points to a task
gate, the processor executes a task switch to the exception- or interrupt-handler task in a manner similar to a CALL
to a task gate (see Section 7.3, “Task Switching”).
6.12.1
Exception- or Interrupt-Handler Procedures
An interrupt gate or trap gate references an exception- or interrupt-handler procedure that runs in the context of
the currently executing task (see Figure 6-3). The segment selector for the gate points to a segment descriptor for
an executable code segment in either the GDT or the current LDT. The offset field of the gate descriptor points to
the beginning of the exception- or interrupt-handling procedure.
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INTERRUPT AND EXCEPTION HANDLING
Destination
Code Segment
IDT
Offset
Interrupt
Vector
Interrupt or
Trap Gate
+
Interrupt
Procedure
Segment Selector
GDT or LDT
Base
Address
Segment
Descriptor
Figure 6-3. Interrupt Procedure Call
When the processor performs a call to the exception- or interrupt-handler procedure:
•
If the handler procedure is going to be executed at a numerically lower privilege level, a stack switch occurs.
When the stack switch occurs:
a. The segment selector and stack pointer for the stack to be used by the handler are obtained from the TSS
for the currently executing task. On this new stack, the processor pushes the stack segment selector and
stack pointer of the interrupted procedure.
b. The processor then saves the current state of the EFLAGS, CS, and EIP registers on the new stack (see
Figures 6-4).
c.
•
If an exception causes an error code to be saved, it is pushed on the new stack after the EIP value.
If the handler procedure is going to be executed at the same privilege level as the interrupted procedure:
a. The processor saves the current state of the EFLAGS, CS, and EIP registers on the current stack (see
Figures 6-4).
b. If an exception causes an error code to be saved, it is pushed on the current stack after the EIP value.
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INTERRUPT AND EXCEPTION HANDLING
Stack Usage with No
Privilege-Level Change
Interrupted Procedure’s
and Handler’s Stack
EFLAGS
CS
EIP
Error Code
ESP Before
Transfer to Handler
ESP After
Transfer to Handler
Stack Usage with
Privilege-Level Change
Interrupted Procedure’s
Stack
Handler’s Stack
ESP Before
Transfer to Handler
ESP After
Transfer to Handler
SS
ESP
EFLAGS
CS
EIP
Error Code
Figure 6-4. Stack Usage on Transfers to Interrupt and Exception-Handling Routines
To return from an exception- or interrupt-handler procedure, the handler must use the IRET (or IRETD) instruction.
The IRET instruction is similar to the RET instruction except that it restores the saved flags into the EFLAGS
register. The IOPL field of the EFLAGS register is restored only if the CPL is 0. The IF flag is changed only if the CPL
is less than or equal to the IOPL. See Chapter 3, “Instruction Set Reference, A-L,” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A, for a description of the complete operation performed by the
IRET instruction.
If a stack switch occurred when calling the handler procedure, the IRET instruction switches back to the interrupted
procedure’s stack on the return.
6.12.1.1
Protection of Exception- and Interrupt-Handler Procedures
The privilege-level protection for exception- and interrupt-handler procedures is similar to that used for ordinary
procedure calls when called through a call gate (see Section 5.8.4, “Accessing a Code Segment Through a Call
Gate”). The processor does not permit transfer of execution to an exception- or interrupt-handler procedure in a
less privileged code segment (numerically greater privilege level) than the CPL.
An attempt to violate this rule results in a general-protection exception (#GP). The protection mechanism for
exception- and interrupt-handler procedures is different in the following ways:
•
Because interrupt and exception vectors have no RPL, the RPL is not checked on implicit calls to exception and
interrupt handlers.
•
The processor checks the DPL of the interrupt or trap gate only if an exception or interrupt is generated with an
INT n, INT 3, or INTO instruction. Here, the CPL must be less than or equal to the DPL of the gate. This
restriction prevents application programs or procedures running at privilege level 3 from using a software
interrupt to access critical exception handlers, such as the page-fault handler, providing that those handlers are
placed in more privileged code segments (numerically lower privilege level). For hardware-generated
interrupts and processor-detected exceptions, the processor ignores the DPL of interrupt and trap gates.
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INTERRUPT AND EXCEPTION HANDLING
Because exceptions and interrupts generally do not occur at predictable times, these privilege rules effectively
impose restrictions on the privilege levels at which exception and interrupt- handling procedures can run. Either of
the following techniques can be used to avoid privilege-level violations.
•
The exception or interrupt handler can be placed in a conforming code segment. This technique can be used for
handlers that only need to access data available on the stack (for example, divide error exceptions). If the
handler needs data from a data segment, the data segment needs to be accessible from privilege level 3, which
would make it unprotected.
•
The handler can be placed in a nonconforming code segment with privilege level 0. This handler would always
run, regardless of the CPL that the interrupted program or task is running at.
6.12.1.2
Flag Usage By Exception- or Interrupt-Handler Procedure
When accessing an exception or interrupt handler through either an interrupt gate or a trap gate, the processor
clears the TF flag in the EFLAGS register after it saves the contents of the EFLAGS register on the stack. (On calls
to exception and interrupt handlers, the processor also clears the VM, RF, and NT flags in the EFLAGS register, after
they are saved on the stack.) Clearing the TF flag prevents instruction tracing from affecting interrupt response. A
subsequent IRET instruction restores the TF (and VM, RF, and NT) flags to the values in the saved contents of the
EFLAGS register on the stack.
The only difference between an interrupt gate and a trap gate is the way the processor handles the IF flag in the
EFLAGS register. When accessing an exception- or interrupt-handling procedure through an interrupt gate, the
processor clears the IF flag to prevent other interrupts from interfering with the current interrupt handler. A subsequent IRET instruction restores the IF flag to its value in the saved contents of the EFLAGS register on the stack.
Accessing a handler procedure through a trap gate does not affect the IF flag.
6.12.2
Interrupt Tasks
When an exception or interrupt handler is accessed through a task gate in the IDT, a task switch results. Handling
an exception or interrupt with a separate task offers several advantages:
•
•
The entire context of the interrupted program or task is saved automatically.
•
The handler can be further isolated from other tasks by giving it a separate address space. This is done by
giving it a separate LDT.
A new TSS permits the handler to use a new privilege level 0 stack when handling the exception or interrupt. If
an exception or interrupt occurs when the current privilege level 0 stack is corrupted, accessing the handler
through a task gate can prevent a system crash by providing the handler with a new privilege level 0 stack.
The disadvantage of handling an interrupt with a separate task is that the amount of machine state that must be
saved on a task switch makes it slower than using an interrupt gate, resulting in increased interrupt latency.
A task gate in the IDT references a TSS descriptor in the GDT (see Figure 6-5). A switch to the handler task is
handled in the same manner as an ordinary task switch (see Section 7.3, “Task Switching”). The link back to the
interrupted task is stored in the previous task link field of the handler task’s TSS. If an exception caused an error
code to be generated, this error code is copied to the stack of the new task.
When exception- or interrupt-handler tasks are used in an operating system, there are actually two mechanisms
that can be used to dispatch tasks: the software scheduler (part of the operating system) and the hardware scheduler (part of the processor's interrupt mechanism). The software scheduler needs to accommodate interrupt tasks
that may be dispatched when interrupts are enabled.
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INTERRUPT AND EXCEPTION HANDLING
NOTE
Because IA-32 architecture tasks are not re-entrant, an interrupt-handler task must disable
interrupts between the time it completes handling the interrupt and the time it executes the IRET
instruction. This action prevents another interrupt from occurring while the interrupt task’s TSS is
still marked busy, which would cause a general-protection (#GP) exception.
IDT
Interrupt
Vector
TSS for InterruptHandling Task
Task Gate
TSS Selector
GDT
TSS
Base
Address
TSS Descriptor
Figure 6-5. Interrupt Task Switch
6.13
ERROR CODE
When an exception condition is related to a specific segment selector or IDT vector, the processor pushes an error
code onto the stack of the exception handler (whether it is a procedure or task). The error code has the format
shown in Figure 6-6. The error code resembles a segment selector; however, instead of a TI flag and RPL field, the
error code contains 3 flags:
EXT
External event (bit 0) — When set, indicates that the exception occurred during delivery of an
event external to the program, such as an interrupt or an earlier exception.
IDT
Descriptor location (bit 1) — When set, indicates that the index portion of the error code refers
to a gate descriptor in the IDT; when clear, indicates that the index refers to a descriptor in the GDT
or the current LDT.
TI
GDT/LDT (bit 2) — Only used when the IDT flag is clear. When set, the TI flag indicates that the
index portion of the error code refers to a segment or gate descriptor in the LDT; when clear, it indicates that the index refers to a descriptor in the current GDT.
Vol. 3A 6-15
INTERRUPT AND EXCEPTION HANDLING
31
3 2 1 0
Reserved
Segment Selector Index
T I E
X
I D
T T
Figure 6-6. Error Code
The segment selector index field provides an index into the IDT, GDT, or current LDT to the segment or gate
selector being referenced by the error code. In some cases the error code is null (all bits are clear except possibly
EXT). A null error code indicates that the error was not caused by a reference to a specific segment or that a null
segment descriptor was referenced in an operation.
The format of the error code is different for page-fault exceptions (#PF). See the “Interrupt 14—Page-Fault Exception (#PF)” section in this chapter.
The error code is pushed on the stack as a doubleword or word (depending on the default interrupt, trap, or task
gate size). To keep the stack aligned for doubleword pushes, the upper half of the error code is reserved. Note that
the error code is not popped when the IRET instruction is executed to return from an exception handler, so the
handler must remove the error code before executing a return.
Error codes are not pushed on the stack for exceptions that are generated externally (with the INTR or LINT[1:0]
pins) or the INT n instruction, even if an error code is normally produced for those exceptions.
6.14
EXCEPTION AND INTERRUPT HANDLING IN 64-BIT MODE
In 64-bit mode, interrupt and exception handling is similar to what has been described for non-64-bit modes. The
following are the exceptions:
•
•
•
All interrupt handlers pointed by the IDT are in 64-bit code (this does not apply to the SMI handler).
•
•
•
•
The new SS is set to NULL if there is a change in CPL.
The size of interrupt-stack pushes is fixed at 64 bits; and the processor uses 8-byte, zero extended stores.
The stack pointer (SS:RSP) is pushed unconditionally on interrupts. In legacy modes, this push is conditional
and based on a change in current privilege level (CPL).
IRET behavior changes.
There is a new interrupt stack-switch mechanism.
The alignment of interrupt stack frame is different.
6.14.1
64-Bit Mode IDT
Interrupt and trap gates are 16 bytes in length to provide a 64-bit offset for the instruction pointer (RIP). The 64bit RIP referenced by interrupt-gate descriptors allows an interrupt service routine to be located anywhere in the
linear-address space. See Figure 6-7.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt/Trap Gate
31
0
Reserved
12
31
0
Offset 63..32
31
8
16 15 14 13 12 11
Offset 31..16
P
D
P
0
8 7
TYPE
5 4
0
2
0 0 0 0 0
4
IST
L
31
16 15
Segment Selector
DPL
Offset
P
Selector
IST
0
Offset 15..0
0
Descriptor Privilege Level
Offset to procedure entry point
Segment Present flag
Segment Selector for destination code segment
Interrupt Stack Table
Figure 6-7. 64-Bit IDT Gate Descriptors
In 64-bit mode, the IDT index is formed by scaling the interrupt vector by 16. The first eight bytes (bytes 7:0) of a
64-bit mode interrupt gate are similar but not identical to legacy 32-bit interrupt gates. The type field (bits 11:8 in
bytes 7:4) is described in Table 3-2. The Interrupt Stack Table (IST) field (bits 4:0 in bytes 7:4) is used by the stack
switching mechanisms described in Section 6.14.5, “Interrupt Stack Table.” Bytes 11:8 hold the upper 32 bits of
the target RIP (interrupt segment offset) in canonical form. A general-protection exception (#GP) is generated if
software attempts to reference an interrupt gate with a target RIP that is not in canonical form.
The target code segment referenced by the interrupt gate must be a 64-bit code segment (CS.L = 1, CS.D = 0). If
the target is not a 64-bit code segment, a general-protection exception (#GP) is generated with the IDT vector
number reported as the error code.
Only 64-bit interrupt and trap gates can be referenced in IA-32e mode (64-bit mode and compatibility mode).
Legacy 32-bit interrupt or trap gate types (0EH or 0FH) are redefined in IA-32e mode as 64-bit interrupt and trap
gate types. No 32-bit interrupt or trap gate type exists in IA-32e mode. If a reference is made to a 16-bit interrupt
or trap gate (06H or 07H), a general-protection exception (#GP(0)) is generated.
6.14.2
64-Bit Mode Stack Frame
In legacy mode, the size of an IDT entry (16 bits or 32 bits) determines the size of interrupt-stack-frame pushes.
SS:ESP is pushed only on a CPL change. In 64-bit mode, the size of interrupt stack-frame pushes is fixed at eight
bytes. This is because only 64-bit mode gates can be referenced. 64-bit mode also pushes SS:RSP unconditionally,
rather than only on a CPL change.
Aside from error codes, pushing SS:RSP unconditionally presents operating systems with a consistent interruptstackframe size across all interrupts. Interrupt service-routine entry points that handle interrupts generated by the
INTn instruction or external INTR# signal can push an additional error code place-holder to maintain consistency.
In legacy mode, the stack pointer may be at any alignment when an interrupt or exception causes a stack frame to
be pushed. This causes the stack frame and succeeding pushes done by an interrupt handler to be at arbitrary
alignments. In IA-32e mode, the RSP is aligned to a 16-byte boundary before pushing the stack frame. The stack
frame itself is aligned on a 16-byte boundary when the interrupt handler is called. The processor can arbitrarily
realign the new RSP on interrupts because the previous (possibly unaligned) RSP is unconditionally saved on the
newly aligned stack. The previous RSP will be automatically restored by a subsequent IRET.
Aligning the stack permits exception and interrupt frames to be aligned on a 16-byte boundary before interrupts
are re-enabled. This allows the stack to be formatted for optimal storage of 16-byte XMM registers, which enables
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the interrupt handler to use faster 16-byte aligned loads and stores (MOVAPS rather than MOVUPS) to save and
restore XMM registers.
Although the RSP alignment is always performed when LMA = 1, it is only of consequence for the kernel-mode case
where there is no stack switch or IST used. For a stack switch or IST, the OS would have presumably put suitably
aligned RSP values in the TSS.
6.14.3
IRET in IA-32e Mode
In IA-32e mode, IRET executes with an 8-byte operand size. There is nothing that forces this requirement. The
stack is formatted in such a way that for actions where IRET is required, the 8-byte IRET operand size works
correctly.
Because interrupt stack-frame pushes are always eight bytes in IA-32e mode, an IRET must pop eight byte items
off the stack. This is accomplished by preceding the IRET with a 64-bit operand-size prefix. The size of the pop is
determined by the address size of the instruction. The SS/ESP/RSP size adjustment is determined by the stack size.
IRET pops SS:RSP unconditionally off the interrupt stack frame only when it is executed in 64-bit mode. In compatibility mode, IRET pops SS:RSP off the stack only if there is a CPL change. This allows legacy applications to
execute properly in compatibility mode when using the IRET instruction. 64-bit interrupt service routines that exit
with an IRET unconditionally pop SS:RSP off of the interrupt stack frame, even if the target code segment is
running in 64-bit mode or at CPL = 0. This is because the original interrupt always pushes SS:RSP.
In IA-32e mode, IRET is allowed to load a NULL SS under certain conditions. If the target mode is 64-bit mode and
the target CPL <> 3, IRET allows SS to be loaded with a NULL selector. As part of the stack switch mechanism, an
interrupt or exception sets the new SS to NULL, instead of fetching a new SS selector from the TSS and loading the
corresponding descriptor from the GDT or LDT. The new SS selector is set to NULL in order to properly handle
returns from subsequent nested far transfers. If the called procedure itself is interrupted, the NULL SS is pushed on
the stack frame. On the subsequent IRET, the NULL SS on the stack acts as a flag to tell the processor not to load
a new SS descriptor.
6.14.4
Stack Switching in IA-32e Mode
The IA-32 architecture provides a mechanism to automatically switch stack frames in response to an interrupt. The
64-bit extensions of Intel 64 architecture implement a modified version of the legacy stack-switching mechanism
and an alternative stack-switching mechanism called the interrupt stack table (IST).
In IA-32 modes, the legacy IA-32 stack-switch mechanism is unchanged. In IA-32e mode, the legacy stack-switch
mechanism is modified. When stacks are switched as part of a 64-bit mode privilege-level change (resulting from
an interrupt), a new SS descriptor is not loaded. IA-32e mode loads only an inner-level RSP from the TSS. The new
SS selector is forced to NULL and the SS selector’s RPL field is set to the new CPL. The new SS is set to NULL in
order to handle nested far transfers (CALLF, INT, interrupts and exceptions). The old SS and RSP are saved on the
new stack (Figure 6-8). On the subsequent IRET, the old SS is popped from the stack and loaded into the SS
register.
In summary, a stack switch in IA-32e mode works like the legacy stack switch, except that a new SS selector is not
loaded from the TSS. Instead, the new SS is forced to NULL.
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INTERRUPT AND EXCEPTION HANDLING
Legacy Mode
+20
+16
+12
+8
+4
0
Stack Usage with
Privilege-Level Change
IA-32e Mode
Handler’s Stack
Handler’s Stack
SS
ESP
EFLAGS
CS
EIP
Error Code
SS
RSP
RFLAGS
CS
RIP
Error Code
Stack Pointer After
Transfer to Handler
+40
+32
+24
+16
+8
0
Figure 6-8. IA-32e Mode Stack Usage After Privilege Level Change
6.14.5
Interrupt Stack Table
In IA-32e mode, a new interrupt stack table (IST) mechanism is available as an alternative to the modified legacy
stack-switching mechanism described above. This mechanism unconditionally switches stacks when it is enabled.
It can be enabled on an individual interrupt-vector basis using a field in the IDT entry. This means that some interrupt vectors can use the modified legacy mechanism and others can use the IST mechanism.
The IST mechanism is only available in IA-32e mode. It is part of the 64-bit mode TSS. The motivation for the IST
mechanism is to provide a method for specific interrupts (such as NMI, double-fault, and machine-check) to always
execute on a known good stack. In legacy mode, interrupts can use the task-switch mechanism to set up a knowngood stack by accessing the interrupt service routine through a task gate located in the IDT. However, the legacy
task-switch mechanism is not supported in IA-32e mode.
The IST mechanism provides up to seven IST pointers in the TSS. The pointers are referenced by an interrupt-gate
descriptor in the interrupt-descriptor table (IDT); see Figure 6-7. The gate descriptor contains a 3-bit IST index
field that provides an offset into the IST section of the TSS. Using the IST mechanism, the processor loads the
value pointed by an IST pointer into the RSP.
When an interrupt occurs, the new SS selector is forced to NULL and the SS selector’s RPL field is set to the new
CPL. The old SS, RSP, RFLAGS, CS, and RIP are pushed onto the new stack. Interrupt processing then proceeds as
normal. If the IST index is zero, the modified legacy stack-switching mechanism described above is used.
6.15
EXCEPTION AND INTERRUPT REFERENCE
The following sections describe conditions which generate exceptions and interrupts. They are arranged in the
order of vector numbers. The information contained in these sections are as follows:
•
Exception Class — Indicates whether the exception class is a fault, trap, or abort type. Some exceptions can
be either a fault or trap type, depending on when the error condition is detected. (This section is not applicable
to interrupts.)
•
Description — Gives a general description of the purpose of the exception or interrupt type. It also describes
how the processor handles the exception or interrupt.
•
Exception Error Code — Indicates whether an error code is saved for the exception. If one is saved, the
contents of the error code are described. (This section is not applicable to interrupts.)
•
Saved Instruction Pointer — Describes which instruction the saved (or return) instruction pointer points to.
It also indicates whether the pointer can be used to restart a faulting instruction.
•
Program State Change — Describes the effects of the exception or interrupt on the state of the currently
running program or task and the possibilities of restarting the program or task without loss of continuity.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt 0—Divide Error Exception (#DE)
Exception Class
Fault.
Description
Indicates the divisor operand for a DIV or IDIV instruction is 0 or that the result cannot be represented in the
number of bits specified for the destination operand.
Exception Error Code
None.
Saved Instruction Pointer
Saved contents of CS and EIP registers point to the instruction that generated the exception.
Program State Change
A program-state change does not accompany the divide error, because the exception occurs before the faulting
instruction is executed.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt 1—Debug Exception (#DB)
Trap or Fault. The exception handler can distinguish between traps or faults by examining the contents of DR6 and the other debug registers.
Exception Class
Description
Indicates that one or more of several debug-exception conditions has been detected. Whether the exception is a
fault or a trap depends on the condition (see Table 6-3). See Chapter 17, “Debugging, Branch Profiling, and TimeStamp Counter,” for detailed information about the debug exceptions.
Table 6-3. Debug Exception Conditions and Corresponding Exception Classes
Exception Condition
Exception Class
Instruction fetch breakpoint
Fault
Data read or write breakpoint
Trap
I/O read or write breakpoint
Trap
General detect condition (in conjunction with in-circuit emulation)
Fault
Single-step
Trap
Task-switch
Trap
Exception Error Code
None. An exception handler can examine the debug registers to determine which condition caused the exception.
Saved Instruction Pointer
Fault — Saved contents of CS and EIP registers point to the instruction that generated the exception.
Trap — Saved contents of CS and EIP registers point to the instruction following the instruction that generated the
exception.
Program State Change
Fault — A program-state change does not accompany the debug exception, because the exception occurs before
the faulting instruction is executed. The program can resume normal execution upon returning from the debug
exception handler.
Trap — A program-state change does accompany the debug exception, because the instruction or task switch being
executed is allowed to complete before the exception is generated. However, the new state of the program is not
corrupted and execution of the program can continue reliably.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt 2—NMI Interrupt
Exception Class
Not applicable.
Description
The nonmaskable interrupt (NMI) is generated externally by asserting the processor’s NMI pin or through an NMI
request set by the I/O APIC to the local APIC. This interrupt causes the NMI interrupt handler to be called.
Exception Error Code
Not applicable.
Saved Instruction Pointer
The processor always takes an NMI interrupt on an instruction boundary. The saved contents of CS and EIP registers point to the next instruction to be executed at the point the interrupt is taken. See Section 6.5, “Exception
Classifications,” for more information about when the processor takes NMI interrupts.
Program State Change
The instruction executing when an NMI interrupt is received is completed before the NMI is generated. A program
or task can thus be restarted upon returning from an interrupt handler without loss of continuity, provided the
interrupt handler saves the state of the processor before handling the interrupt and restores the processor’s state
prior to a return.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt 3—Breakpoint Exception (#BP)
Exception Class
Trap.
Description
Indicates that a breakpoint instruction (INT 3) was executed, causing a breakpoint trap to be generated. Typically,
a debugger sets a breakpoint by replacing the first opcode byte of an instruction with the opcode for the INT 3
instruction. (The INT 3 instruction is one byte long, which makes it easy to replace an opcode in a code segment in
RAM with the breakpoint opcode.) The operating system or a debugging tool can use a data segment mapped to
the same physical address space as the code segment to place an INT 3 instruction in places where it is desired to
call the debugger.
With the P6 family, Pentium, Intel486, and Intel386 processors, it is more convenient to set breakpoints with the
debug registers. (See Section 17.3.2, “Breakpoint Exception (#BP)—Interrupt Vector 3,” for information about the
breakpoint exception.) If more breakpoints are needed beyond what the debug registers allow, the INT 3 instruction can be used.
The breakpoint (#BP) exception can also be generated by executing the INT n instruction with an operand of 3. The
action of this instruction (INT 3) is slightly different than that of the INT 3 instruction (see “INTn/INTO/INT3—Call
to Interrupt Procedure” in Chapter 3 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 2A).
Exception Error Code
None.
Saved Instruction Pointer
Saved contents of CS and EIP registers point to the instruction following the INT 3 instruction.
Program State Change
Even though the EIP points to the instruction following the breakpoint instruction, the state of the program is
essentially unchanged because the INT 3 instruction does not affect any register or memory locations. The
debugger can thus resume the suspended program by replacing the INT 3 instruction that caused the breakpoint
with the original opcode and decrementing the saved contents of the EIP register. Upon returning from the
debugger, program execution resumes with the replaced instruction.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt 4—Overflow Exception (#OF)
Exception Class
Trap.
Description
Indicates that an overflow trap occurred when an INTO instruction was executed. The INTO instruction checks the
state of the OF flag in the EFLAGS register. If the OF flag is set, an overflow trap is generated.
Some arithmetic instructions (such as the ADD and SUB) perform both signed and unsigned arithmetic. These
instructions set the OF and CF flags in the EFLAGS register to indicate signed overflow and unsigned overflow,
respectively. When performing arithmetic on signed operands, the OF flag can be tested directly or the INTO
instruction can be used. The benefit of using the INTO instruction is that if the overflow exception is detected, an
exception handler can be called automatically to handle the overflow condition.
Exception Error Code
None.
Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction following the INTO instruction.
Program State Change
Even though the EIP points to the instruction following the INTO instruction, the state of the program is essentially
unchanged because the INTO instruction does not affect any register or memory locations. The program can thus
resume normal execution upon returning from the overflow exception handler.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt 5—BOUND Range Exceeded Exception (#BR)
Exception Class
Fault.
Description
Indicates that a BOUND-range-exceeded fault occurred when a BOUND instruction was executed. The BOUND
instruction checks that a signed array index is within the upper and lower bounds of an array located in memory. If
the array index is not within the bounds of the array, a BOUND-range-exceeded fault is generated.
Exception Error Code
None.
Saved Instruction Pointer
The saved contents of CS and EIP registers point to the BOUND instruction that generated the exception.
Program State Change
A program-state change does not accompany the bounds-check fault, because the operands for the BOUND
instruction are not modified. Returning from the BOUND-range-exceeded exception handler causes the BOUND
instruction to be restarted.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt 6—Invalid Opcode Exception (#UD)
Exception Class
Fault.
Description
Indicates that the processor did one of the following things:
•
•
Attempted to execute an invalid or reserved opcode.
•
Attempted to execute an MMX or SSE/SSE2/SSE3 instruction on an Intel 64 or IA-32 processor that does not
support the MMX technology or SSE/SSE2/SSE3/SSSE3 extensions, respectively. CPUID feature flags MMX (bit
23), SSE (bit 25), SSE2 (bit 26), SSE3 (ECX, bit 0), SSSE3 (ECX, bit 9) indicate support for these extensions.
•
Attempted to execute an MMX instruction or SSE/SSE2/SSE3/SSSE3 SIMD instruction (with the exception of
the MOVNTI, PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE, CLFLUSH, MONITOR, and MWAIT instructions)
when the EM flag in control register CR0 is set (1).
•
Attempted to execute an SSE/SE2/SSE3/SSSE3 instruction when the OSFXSR bit in control register CR4 is clear
(0). Note this does not include the following SSE/SSE2/SSE3 instructions: MASKMOVQ, MOVNTQ, MOVNTI,
PREFETCHh, SFENCE, LFENCE, MFENCE, and CLFLUSH; or the 64-bit versions of the PAVGB, PAVGW, PEXTRW,
PINSRW, PMAXSW, PMAXUB, PMINSW, PMINUB, PMOVMSKB, PMULHUW, PSADBW, PSHUFW, PADDQ, PSUBQ,
PALIGNR, PABSB, PABSD, PABSW, PHADDD, PHADDSW, PHADDW, PHSUBD, PHSUBSW, PHSUBW,
PMADDUBSM, PMULHRSW, PSHUFB, PSIGNB, PSIGND, and PSIGNW.
•
Attempted to execute an SSE/SSE2/SSE3/SSSE3 instruction on an Intel 64 or IA-32 processor that caused a
SIMD floating-point exception when the OSXMMEXCPT bit in control register CR4 is clear (0).
•
Executed a UD2 instruction. Note that even though it is the execution of the UD2 instruction that causes the
invalid opcode exception, the saved instruction pointer will still points at the UD2 instruction.
•
Detected a LOCK prefix that precedes an instruction that may not be locked or one that may be locked but the
destination operand is not a memory location.
•
Attempted to execute an LLDT, SLDT, LTR, STR, LSL, LAR, VERR, VERW, or ARPL instruction while in realaddress or virtual-8086 mode.
•
Attempted to execute the RSM instruction when not in SMM mode.
Attempted to execute an instruction with an operand type that is invalid for its accompanying opcode; for
example, the source operand for a LES instruction is not a memory location.
In Intel 64 and IA-32 processors that implement out-of-order execution microarchitectures, this exception is not
generated until an attempt is made to retire the result of executing an invalid instruction; that is, decoding and
speculatively attempting to execute an invalid opcode does not generate this exception. Likewise, in the Pentium
processor and earlier IA-32 processors, this exception is not generated as the result of prefetching and preliminary
decoding of an invalid instruction. (See Section 6.5, “Exception Classifications,” for general rules for taking of interrupts and exceptions.)
The opcodes D6 and F1 are undefined opcodes reserved by the Intel 64 and IA-32 architectures. These opcodes,
even though undefined, do not generate an invalid opcode exception.
The UD2 instruction is guaranteed to generate an invalid opcode exception.
Exception Error Code
None.
Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction that generated the exception.
Program State Change
A program-state change does not accompany an invalid-opcode fault, because the invalid instruction is not
executed.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt 7—Device Not Available Exception (#NM)
Exception Class
Fault.
Description
Indicates one of the following things:
The device-not-available exception is generated by either of three conditions:
•
The processor executed an x87 FPU floating-point instruction while the EM flag in control register CR0 was set
(1). See the paragraph below for the special case of the WAIT/FWAIT instruction.
•
The processor executed a WAIT/FWAIT instruction while the MP and TS flags of register CR0 were set,
regardless of the setting of the EM flag.
•
The processor executed an x87 FPU, MMX, or SSE/SSE2/SSE3 instruction (with the exception of MOVNTI,
PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE, and CLFLUSH) while the TS flag in control register CR0 was set
and the EM flag is clear.
The EM flag is set when the processor does not have an internal x87 FPU floating-point unit. A device-not-available
exception is then generated each time an x87 FPU floating-point instruction is encountered, allowing an exception
handler to call floating-point instruction emulation routines.
The TS flag indicates that a context switch (task switch) has occurred since the last time an x87 floating-point,
MMX, or SSE/SSE2/SSE3 instruction was executed; but that the context of the x87 FPU, XMM, and MXCSR registers
were not saved. When the TS flag is set and the EM flag is clear, the processor generates a device-not-available
exception each time an x87 floating-point, MMX, or SSE/SSE2/SSE3 instruction is encountered (with the exception
of the instructions listed above). The exception handler can then save the context of the x87 FPU, XMM, and MXCSR
registers before it executes the instruction. See Section 2.5, “Control Registers,” for more information about the TS
flag.
The MP flag in control register CR0 is used along with the TS flag to determine if WAIT or FWAIT instructions should
generate a device-not-available exception. It extends the function of the TS flag to the WAIT and FWAIT instructions, giving the exception handler an opportunity to save the context of the x87 FPU before the WAIT or FWAIT
instruction is executed. The MP flag is provided primarily for use with the Intel 286 and Intel386 DX processors. For
programs running on the Pentium 4, Intel Xeon, P6 family, Pentium, or Intel486 DX processors, or the Intel 487 SX
coprocessors, the MP flag should always be set; for programs running on the Intel486 SX processor, the MP flag
should be clear.
Exception Error Code
None.
Saved Instruction Pointer
The saved contents of CS and EIP registers point to the floating-point instruction or the WAIT/FWAIT instruction
that generated the exception.
Program State Change
A program-state change does not accompany a device-not-available fault, because the instruction that generated
the exception is not executed.
If the EM flag is set, the exception handler can then read the floating-point instruction pointed to by the EIP and
call the appropriate emulation routine.
If the MP and TS flags are set or the TS flag alone is set, the exception handler can save the context of the x87 FPU,
clear the TS flag, and continue execution at the interrupted floating-point or WAIT/FWAIT instruction.
Vol. 3A 6-27
INTERRUPT AND EXCEPTION HANDLING
Interrupt 8—Double Fault Exception (#DF)
Exception Class
Abort.
Description
Indicates that the processor detected a second exception while calling an exception handler for a prior exception.
Normally, when the processor detects another exception while trying to call an exception handler, the two exceptions can be handled serially. If, however, the processor cannot handle them serially, it signals the double-fault
exception. To determine when two faults need to be signalled as a double fault, the processor divides the exceptions into three classes: benign exceptions, contributory exceptions, and page faults (see Table 6-4).
Table 6-4. Interrupt and Exception Classes
Class
Vector Number
Description
Benign Exceptions and Interrupts
1
2
3
4
5
6
7
9
16
17
18
Debug
NMI Interrupt
Breakpoint
Overflow
BOUND Range Exceeded
Invalid Opcode
Device Not Available
Coprocessor Segment Overrun
Floating-Point Error
Alignment Check
Machine Check
19
All
All
SIMD floating-point
INT n
INTR
Contributory Exceptions
0
10
11
12
13
Divide Error
Invalid TSS
Segment Not Present
Stack Fault
General Protection
Page Faults
14
20
Page Fault
Virtualization Exception
Table 6-5 shows the various combinations of exception classes that cause a double fault to be generated. A doublefault exception falls in the abort class of exceptions. The program or task cannot be restarted or resumed. The
double-fault handler can be used to collect diagnostic information about the state of the machine and/or, when
possible, to shut the application and/or system down gracefully or restart the system.
A segment or page fault may be encountered while prefetching instructions; however, this behavior is outside the
domain of Table 6-5. Any further faults generated while the processor is attempting to transfer control to the appropriate fault handler could still lead to a double-fault sequence.
Table 6-5. Conditions for Generating a Double Fault
Second Exception
First Exception
Benign
Contributory
Page Fault
Benign
Handle Exceptions Serially
Handle Exceptions Serially
Handle Exceptions Serially
Contributory
Handle Exceptions Serially
Generate a Double Fault
Handle Exceptions Serially
Page Fault
Handle Exceptions Serially
Generate a Double Fault
Generate a Double Fault
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INTERRUPT AND EXCEPTION HANDLING
If another exception occurs while attempting to call the double-fault handler, the processor enters shutdown mode.
This mode is similar to the state following execution of an HLT instruction. In this mode, the processor stops
executing instructions until an NMI interrupt, SMI interrupt, hardware reset, or INIT# is received. The processor
generates a special bus cycle to indicate that it has entered shutdown mode. Software designers may need to be
aware of the response of hardware when it goes into shutdown mode. For example, hardware may turn on an indicator light on the front panel, generate an NMI interrupt to record diagnostic information, invoke reset initialization, generate an INIT initialization, or generate an SMI. If any events are pending during shutdown, they will be
handled after an wake event from shutdown is processed (for example, A20M# interrupts).
If a shutdown occurs while the processor is executing an NMI interrupt handler, then only a hardware reset can
restart the processor. Likewise, if the shutdown occurs while executing in SMM, a hardware reset must be used to
restart the processor.
Exception Error Code
Zero. The processor always pushes an error code of 0 onto the stack of the double-fault handler.
Saved Instruction Pointer
The saved contents of CS and EIP registers are undefined.
Program State Change
A program-state following a double-fault exception is undefined. The program or task cannot be resumed or
restarted. The only available action of the double-fault exception handler is to collect all possible context information for use in diagnostics and then close the application and/or shut down or reset the processor.
If the double fault occurs when any portion of the exception handling machine state is corrupted, the handler
cannot be invoked and the processor must be reset.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt 9—Coprocessor Segment Overrun
Exception Class
Abort. (Intel reserved; do not use. Recent IA-32 processors do not generate this
exception.)
Description
Indicates that an Intel386 CPU-based systems with an Intel 387 math coprocessor detected a page or segment
violation while transferring the middle portion of an Intel 387 math coprocessor operand. The P6 family, Pentium,
and Intel486 processors do not generate this exception; instead, this condition is detected with a general protection exception (#GP), interrupt 13.
Exception Error Code
None.
Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction that generated the exception.
Program State Change
A program-state following a coprocessor segment-overrun exception is undefined. The program or task cannot
be resumed or restarted. The only available action of the exception handler is to save the instruction pointer and
reinitialize the x87 FPU using the FNINIT instruction.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt 10—Invalid TSS Exception (#TS)
Exception Class
Fault.
Description
Indicates that there was an error related to a TSS. Such an error might be detected during a task switch or during
the execution of instructions that use information from a TSS. Table 6-6 shows the conditions that cause an invalid
TSS exception to be generated.
Table 6-6. Invalid TSS Conditions
Error Code Index
Invalid Condition
TSS segment selector index
The TSS segment limit is less than 67H for 32-bit TSS or less than 2CH for 16-bit TSS.
TSS segment selector index
During an IRET task switch, the TI flag in the TSS segment selector indicates the LDT.
TSS segment selector index
During an IRET task switch, the TSS segment selector exceeds descriptor table limit.
TSS segment selector index
During an IRET task switch, the busy flag in the TSS descriptor indicates an inactive task.
TSS segment selector index
During an IRET task switch, an attempt to load the backlink limit faults.
TSS segment selector index
During an IRET task switch, the backlink is a NULL selector.
TSS segment selector index
During an IRET task switch, the backlink points to a descriptor which is not a busy TSS.
TSS segment selector index
The new TSS descriptor is beyond the GDT limit.
TSS segment selector index
The new TSS descriptor is not writable.
TSS segment selector index
Stores to the old TSS encounter a fault condition.
TSS segment selector index
The old TSS descriptor is not writable for a jump or IRET task switch.
TSS segment selector index
The new TSS backlink is not writable for a call or exception task switch.
TSS segment selector index
The new TSS selector is null on an attempt to lock the new TSS.
TSS segment selector index
The new TSS selector has the TI bit set on an attempt to lock the new TSS.
TSS segment selector index
The new TSS descriptor is not an available TSS descriptor on an attempt to lock the new
TSS.
LDT segment selector index
LDT or LDT not present.
Stack segment selector index
The stack segment selector exceeds descriptor table limit.
Stack segment selector index
The stack segment selector is NULL.
Stack segment selector index
The stack segment descriptor is a non-data segment.
Stack segment selector index
The stack segment is not writable.
Stack segment selector index
The stack segment DPL != CPL.
Stack segment selector index
The stack segment selector RPL != CPL.
Code segment selector index
The code segment selector exceeds descriptor table limit.
Code segment selector index
The code segment selector is NULL.
Code segment selector index
The code segment descriptor is not a code segment type.
Code segment selector index
The nonconforming code segment DPL != CPL.
Code segment selector index
The conforming code segment DPL is greater than CPL.
Data segment selector index
The data segment selector exceeds the descriptor table limit.
Data segment selector index
The data segment descriptor is not a readable code or data type.
Data segment selector index
The data segment descriptor is a nonconforming code type and RPL > DPL.
Vol. 3A 6-31
INTERRUPT AND EXCEPTION HANDLING
Table 6-6. Invalid TSS Conditions (Contd.)
Error Code Index
Invalid Condition
Data segment selector index
The data segment descriptor is a nonconforming code type and CPL > DPL.
TSS segment selector index
The TSS segment selector is NULL for LTR.
TSS segment selector index
The TSS segment selector has the TI bit set for LTR.
TSS segment selector index
The TSS segment descriptor/upper descriptor is beyond the GDT segment limit.
TSS segment selector index
The TSS segment descriptor is not an available TSS type.
TSS segment selector index
The TSS segment descriptor is an available 286 TSS type in IA-32e mode.
TSS segment selector index
The TSS segment upper descriptor is not the correct type.
TSS segment selector index
The TSS segment descriptor contains a non-canonical base.
TSS segment selector index
There is a limit violation in attempting to load SS selector or ESP from a TSS on a call or
exception which changes privilege levels in legacy mode.
TSS segment selector index
There is a limit violation or canonical fault in attempting to load RSP or IST from a TSS on a
call or exception which changes privilege levels in IA-32e mode.
This exception can generated either in the context of the original task or in the context of the new task (see Section
7.3, “Task Switching”). Until the processor has completely verified the presence of the new TSS, the exception is
generated in the context of the original task. Once the existence of the new TSS is verified, the task switch is
considered complete. Any invalid-TSS conditions detected after this point are handled in the context of the new
task. (A task switch is considered complete when the task register is loaded with the segment selector for the new
TSS and, if the switch is due to a procedure call or interrupt, the previous task link field of the new TSS references
the old TSS.)
The invalid-TSS handler must be a task called using a task gate. Handling this exception inside the faulting TSS
context is not recommended because the processor state may not be consistent.
Exception Error Code
An error code containing the segment selector index for the segment descriptor that caused the violation is pushed
onto the stack of the exception handler. If the EXT flag is set, it indicates that the exception was caused by an event
external to the currently running program (for example, if an external interrupt handler using a task gate
attempted a task switch to an invalid TSS).
Saved Instruction Pointer
If the exception condition was detected before the task switch was carried out, the saved contents of CS and EIP
registers point to the instruction that invoked the task switch. If the exception condition was detected after the task
switch was carried out, the saved contents of CS and EIP registers point to the first instruction of the new task.
Program State Change
The ability of the invalid-TSS handler to recover from the fault depends on the error condition than causes the fault.
See Section 7.3, “Task Switching,” for more information on the task switch process and the possible recovery
actions that can be taken.
If an invalid TSS exception occurs during a task switch, it can occur before or after the commit-to-new-task point.
If it occurs before the commit point, no program state change occurs. If it occurs after the commit point (when the
segment descriptor information for the new segment selectors have been loaded in the segment registers), the
processor will load all the state information from the new TSS before it generates the exception. During a task
switch, the processor first loads all the segment registers with segment selectors from the TSS, then checks their
contents for validity. If an invalid TSS exception is discovered, the remaining segment registers are loaded but not
checked for validity and therefore may not be usable for referencing memory. The invalid TSS handler should not
rely on being able to use the segment selectors found in the CS, SS, DS, ES, FS, and GS registers without causing
another exception. The exception handler should load all segment registers before trying to resume the new task;
otherwise, general-protection exceptions (#GP) may result later under conditions that make diagnosis more diffi-
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cult. The Intel recommended way of dealing situation is to use a task for the invalid TSS exception handler. The
task switch back to the interrupted task from the invalid-TSS exception-handler task will then cause the processor
to check the registers as it loads them from the TSS.
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Interrupt 11—Segment Not Present (#NP)
Exception Class
Fault.
Description
Indicates that the present flag of a segment or gate descriptor is clear. The processor can generate this exception
during any of the following operations:
•
While attempting to load CS, DS, ES, FS, or GS registers. [Detection of a not-present segment while loading the
SS register causes a stack fault exception (#SS) to be generated.] This situation can occur while performing a
task switch.
•
While attempting to load the LDTR using an LLDT instruction. Detection of a not-present LDT while loading the
LDTR during a task switch operation causes an invalid-TSS exception (#TS) to be generated.
•
•
When executing the LTR instruction and the TSS is marked not present.
While attempting to use a gate descriptor or TSS that is marked segment-not-present, but is otherwise valid.
An operating system typically uses the segment-not-present exception to implement virtual memory at the
segment level. If the exception handler loads the segment and returns, the interrupted program or task resumes
execution.
A not-present indication in a gate descriptor, however, does not indicate that a segment is not present (because
gates do not correspond to segments). The operating system may use the present flag for gate descriptors to
trigger exceptions of special significance to the operating system.
A contributory exception or page fault that subsequently referenced a not-present segment would cause a double
fault (#DF) to be generated instead of #NP.
Exception Error Code
An error code containing the segment selector index for the segment descriptor that caused the violation is pushed
onto the stack of the exception handler. If the EXT flag is set, it indicates that the exception resulted from either:
•
an external event (NMI or INTR) that caused an interrupt, which subsequently referenced a not-present
segment
•
a benign exception that subsequently referenced a not-present segment
The IDT flag is set if the error code refers to an IDT entry. This occurs when the IDT entry for an interrupt being
serviced references a not-present gate. Such an event could be generated by an INT instruction or a hardware
interrupt.
Saved Instruction Pointer
The saved contents of CS and EIP registers normally point to the instruction that generated the exception. If the
exception occurred while loading segment descriptors for the segment selectors in a new TSS, the CS and EIP
registers point to the first instruction in the new task. If the exception occurred while accessing a gate descriptor,
the CS and EIP registers point to the instruction that invoked the access (for example a CALL instruction that references a call gate).
Program State Change
If the segment-not-present exception occurs as the result of loading a register (CS, DS, SS, ES, FS, GS, or LDTR),
a program-state change does accompany the exception because the register is not loaded. Recovery from this
exception is possible by simply loading the missing segment into memory and setting the present flag in the
segment descriptor.
If the segment-not-present exception occurs while accessing a gate descriptor, a program-state change does not
accompany the exception. Recovery from this exception is possible merely by setting the present flag in the gate
descriptor.
If a segment-not-present exception occurs during a task switch, it can occur before or after the commit-to-newtask point (see Section 7.3, “Task Switching”). If it occurs before the commit point, no program state change
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occurs. If it occurs after the commit point, the processor will load all the state information from the new TSS
(without performing any additional limit, present, or type checks) before it generates the exception. The segmentnot-present exception handler should not rely on being able to use the segment selectors found in the CS, SS, DS,
ES, FS, and GS registers without causing another exception. (See the Program State Change description for “Interrupt 10—Invalid TSS Exception (#TS)” in this chapter for additional information on how to handle this situation.)
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Interrupt 12—Stack Fault Exception (#SS)
Exception Class
Fault.
Description
Indicates that one of the following stack related conditions was detected:
•
A limit violation is detected during an operation that refers to the SS register. Operations that can cause a limit
violation include stack-oriented instructions such as POP, PUSH, CALL, RET, IRET, ENTER, and LEAVE, as well as
other memory references which implicitly or explicitly use the SS register (for example, MOV AX, [BP+6] or
MOV AX, SS:[EAX+6]). The ENTER instruction generates this exception when there is not enough stack space
for allocating local variables.
•
A not-present stack segment is detected when attempting to load the SS register. This violation can occur
during the execution of a task switch, a CALL instruction to a different privilege level, a return to a different
privilege level, an LSS instruction, or a MOV or POP instruction to the SS register.
•
A canonical violation is detected in 64-bit mode during an operation that reference memory using the stack
pointer register containing a non-canonical memory address.
Recovery from this fault is possible by either extending the limit of the stack segment (in the case of a limit violation) or loading the missing stack segment into memory (in the case of a not-present violation.
In the case of a canonical violation that was caused intentionally by software, recovery is possible by loading the
correct canonical value into RSP. Otherwise, a canonical violation of the address in RSP likely reflects some register
corruption in the software.
Exception Error Code
If the exception is caused by a not-present stack segment or by overflow of the new stack during an inter-privilegelevel call, the error code contains a segment selector for the segment that caused the exception. Here, the exception handler can test the present flag in the segment descriptor pointed to by the segment selector to determine
the cause of the exception. For a normal limit violation (on a stack segment already in use) the error code is set to
0.
Saved Instruction Pointer
The saved contents of CS and EIP registers generally point to the instruction that generated the exception.
However, when the exception results from attempting to load a not-present stack segment during a task switch,
the CS and EIP registers point to the first instruction of the new task.
Program State Change
A program-state change does not generally accompany a stack-fault exception, because the instruction that generated the fault is not executed. Here, the instruction can be restarted after the exception handler has corrected the
stack fault condition.
If a stack fault occurs during a task switch, it occurs after the commit-to-new-task point (see Section 7.3, “Task
Switching”). Here, the processor loads all the state information from the new TSS (without performing any additional limit, present, or type checks) before it generates the exception. The stack fault handler should thus not rely
on being able to use the segment selectors found in the CS, SS, DS, ES, FS, and GS registers without causing
another exception. The exception handler should check all segment registers before trying to resume the new
task; otherwise, general protection faults may result later under conditions that are more difficult to diagnose. (See
the Program State Change description for “Interrupt 10—Invalid TSS Exception (#TS)” in this chapter for additional
information on how to handle this situation.)
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Interrupt 13—General Protection Exception (#GP)
Exception Class
Fault.
Description
Indicates that the processor detected one of a class of protection violations called “general-protection violations.”
The conditions that cause this exception to be generated comprise all the protection violations that do not cause
other exceptions to be generated (such as, invalid-TSS, segment-not-present, stack-fault, or page-fault exceptions). The following conditions cause general-protection exceptions to be generated:
•
•
Exceeding the segment limit when accessing the CS, DS, ES, FS, or GS segments.
•
•
•
•
Transferring execution to a segment that is not executable.
•
•
•
•
•
•
•
Loading the SS, DS, ES, FS, or GS register with a segment selector for a system segment.
•
•
Violating any of the privilege rules described in Chapter 5, “Protection.”
•
•
•
•
Loading the CR0 register with a set PG flag (paging enabled) and a clear PE flag (protection disabled).
•
•
Attempting to write a 1 into a reserved bit of CR4.
•
•
•
Writing to a reserved bit in an MSR.
•
•
The segment selector in a call, interrupt, or trap gate does not point to a code segment.
•
•
The segment selector operand in the LTR instruction is local or points to a TSS that is not available.
Exceeding the segment limit when referencing a descriptor table (except during a task switch or a stack
switch).
Writing to a code segment or a read-only data segment.
Reading from an execute-only code segment.
Loading the SS register with a segment selector for a read-only segment (unless the selector comes from a TSS
during a task switch, in which case an invalid-TSS exception occurs).
Loading the DS, ES, FS, or GS register with a segment selector for an execute-only code segment.
Loading the SS register with the segment selector of an executable segment or a null segment selector.
Loading the CS register with a segment selector for a data segment or a null segment selector.
Accessing memory using the DS, ES, FS, or GS register when it contains a null segment selector.
Switching to a busy task during a call or jump to a TSS.
Using a segment selector on a non-IRET task switch that points to a TSS descriptor in the current LDT. TSS
descriptors can only reside in the GDT. This condition causes a #TS exception during an IRET task switch.
Exceeding the instruction length limit of 15 bytes (this only can occur when redundant prefixes are placed
before an instruction).
Loading the CR0 register with a set NW flag and a clear CD flag.
Referencing an entry in the IDT (following an interrupt or exception) that is not an interrupt, trap, or task gate.
Attempting to access an interrupt or exception handler through an interrupt or trap gate from virtual-8086
mode when the handler’s code segment DPL is greater than 0.
Attempting to execute a privileged instruction when the CPL is not equal to 0 (see Section 5.9, “Privileged
Instructions,” for a list of privileged instructions).
Accessing a gate that contains a null segment selector.
Executing the INT n instruction when the CPL is greater than the DPL of the referenced interrupt, trap, or task
gate.
The segment selector operand in the LLDT instruction is a local type (TI flag is set) or does not point to a
segment descriptor of the LDT type.
The target code-segment selector for a call, jump, or return is null.
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•
If the PAE and/or PSE flag in control register CR4 is set and the processor detects any reserved bits in a pagedirectory-pointer-table entry set to 1. These bits are checked during a write to control registers CR0, CR3, or
CR4 that causes a reloading of the page-directory-pointer-table entry.
•
•
Attempting to write a non-zero value into the reserved bits of the MXCSR register.
Executing an SSE/SSE2/SSE3 instruction that attempts to access a 128-bit memory location that is not aligned
on a 16-byte boundary when the instruction requires 16-byte alignment. This condition also applies to the stack
segment.
A program or task can be restarted following any general-protection exception. If the exception occurs while
attempting to call an interrupt handler, the interrupted program can be restartable, but the interrupt may be lost.
Exception Error Code
The processor pushes an error code onto the exception handler's stack. If the fault condition was detected while
loading a segment descriptor, the error code contains a segment selector to or IDT vector number for the
descriptor; otherwise, the error code is 0. The source of the selector in an error code may be any of the following:
•
•
•
•
An operand of the instruction.
A selector from a gate which is the operand of the instruction.
A selector from a TSS involved in a task switch.
IDT vector number.
Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction that generated the exception.
Program State Change
In general, a program-state change does not accompany a general-protection exception, because the invalid
instruction or operation is not executed. An exception handler can be designed to correct all of the conditions that
cause general-protection exceptions and restart the program or task without any loss of program continuity.
If a general-protection exception occurs during a task switch, it can occur before or after the commit-to-new-task
point (see Section 7.3, “Task Switching”). If it occurs before the commit point, no program state change occurs. If
it occurs after the commit point, the processor will load all the state information from the new TSS (without
performing any additional limit, present, or type checks) before it generates the exception. The general-protection
exception handler should thus not rely on being able to use the segment selectors found in the CS, SS, DS, ES, FS,
and GS registers without causing another exception. (See the Program State Change description for “Interrupt
10—Invalid TSS Exception (#TS)” in this chapter for additional information on how to handle this situation.)
General Protection Exception in 64-bit Mode
The following conditions cause general-protection exceptions in 64-bit mode:
•
•
•
•
•
If the memory address is in a non-canonical form.
•
•
•
•
•
If the EFLAGS.NT bit is set in IRET.
If a segment descriptor memory address is in non-canonical form.
If the target offset in a destination operand of a call or jmp is in a non-canonical form.
If a code segment or 64-bit call gate overlaps non-canonical space.
If the code segment descriptor pointed to by the selector in the 64-bit gate doesn't have the L-bit set and the
D-bit clear.
If the stack segment selector of IRET is null when going back to compatibility mode.
If the stack segment selector of IRET is null going back to CPL3 and 64-bit mode.
If a null stack segment selector RPL of IRET is not equal to CPL going back to non-CPL3 and 64-bit mode.
If the proposed new code segment descriptor of IRET has both the D-bit and the L-bit set.
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INTERRUPT AND EXCEPTION HANDLING
•
If the segment descriptor pointed to by the segment selector in the destination operand is a code segment and
it has both the D-bit and the L-bit set.
•
•
•
•
•
•
If the segment descriptor from a 64-bit call gate is in non-canonical space.
•
•
If an attempt is made to clear CR0.PG while IA-32e mode is enabled.
If the DPL from a 64-bit call-gate is less than the CPL or than the RPL of the 64-bit call-gate.
If the upper type field of a 64-bit call gate is not 0x0.
If an attempt is made to load a null selector in the SS register in compatibility mode.
If an attempt is made to load null selector in the SS register in CPL3 and 64-bit mode.
If an attempt is made to load a null selector in the SS register in non-CPL3 and 64-bit mode where RPL is not
equal to CPL.
If an attempt is made to set a reserved bit in CR3, CR4 or CR8.
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Interrupt 14—Page-Fault Exception (#PF)
Exception Class
Fault.
Description
Indicates that, with paging enabled (the PG flag in the CR0 register is set), the processor detected one of the
following conditions while using the page-translation mechanism to translate a linear address to a physical
address:
•
The P (present) flag in a page-directory or page-table entry needed for the address translation is clear,
indicating that a page table or the page containing the operand is not present in physical memory.
•
The procedure does not have sufficient privilege to access the indicated page (that is, a procedure running in
user mode attempts to access a supervisor-mode page).
•
Code running in user mode attempts to write to a read-only page. In the Intel486 and later processors, if the
WP flag is set in CR0, the page fault will also be triggered by code running in supervisor mode that tries to write
to a read-only page.
•
An instruction fetch to a linear address that translates to a physical address in a memory page with the
execute-disable bit set (for information about the execute-disable bit, see Chapter 4, “Paging”).
•
One or more reserved bits in page directory entry are set to 1. See description below of RSVD error code flag.
The exception handler can recover from page-not-present conditions and restart the program or task without any
loss of program continuity. It can also restart the program or task after a privilege violation, but the problem that
caused the privilege violation may be uncorrectable.
See also: Section 4.7, “Page-Fault Exceptions.”
Exception Error Code
Yes (special format). The processor provides the page-fault handler with two items of information to aid in diagnosing the exception and recovering from it:
•
An error code on the stack. The error code for a page fault has a format different from that for other exceptions
(see Figure 6-9). The error code tells the exception handler four things:
— The P flag indicates whether the exception was due to a not-present page (0) or to either an access rights
violation or the use of a reserved bit (1).
— The W/R flag indicates whether the memory access that caused the exception was a read (0) or write (1).
— The U/S flag indicates whether the processor was executing at user mode (1) or supervisor mode (0) at the
time of the exception.
— The RSVD flag indicates that the processor detected 1s in reserved bits of the page directory, when the PSE
or PAE flags in control register CR4 are set to 1. Note:
•
The PSE flag is only available in recent Intel 64 and IA-32 processors including the Pentium 4, Intel
Xeon, P6 family, and Pentium processors.
•
The PAE flag is only available on recent Intel 64 and IA-32 processors including the Pentium 4, Intel
Xeon, and P6 family processors.
•
In earlier IA-32 processors, the bit position of the RSVD flag is reserved and is cleared to 0.
— The I/D flag indicates whether the exception was caused by an instruction fetch. This flag is reserved and
cleared to 0 if CR4.SMEP = 0 (supervisor-mode execution prevention is either unsupported or not enabled)
and either CR4.PAE = 0 (32-bit paging is in use) or IA32_EFER.NXE= 0 (the execute-disable feature is
either unsupported or not enabled). See Section 4.7, “Page-Fault Exceptions,” for details.
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INTERRUPT AND EXCEPTION HANDLING
4 3 2 1 0
31
P
W/R
U/S
RSVD
I/D
Reserved
P
0 The fault was caused by a non-present page.
1 The fault was caused by a page-level protection violation.
W/R
0 The access causing the fault was a read.
1 The access causing the fault was a write.
U/S
0 The access causing the fault originated when the processor
was executing in supervisor mode.
1 The access causing the fault originated when the processor
was executing in user mode.
RSVD
0 The fault was not caused by reserved bit violation.
1 The fault was caused by reserved bits set to 1 in a page directory.
I/D
0 The fault was not caused by an instruction fetch.
1 The fault was caused by an instruction fetch.
Figure 6-9. Page-Fault Error Code
•
The contents of the CR2 register. The processor loads the CR2 register with the 32-bit linear address that
generated the exception. The page-fault handler can use this address to locate the corresponding page
directory and page-table entries. Another page fault can potentially occur during execution of the page-fault
handler; the handler should save the contents of the CR2 register before a second page fault can occur.1 If a
page fault is caused by a page-level protection violation, the access flag in the page-directory entry is set when
the fault occurs. The behavior of IA-32 processors regarding the access flag in the corresponding page-table
entry is model specific and not architecturally defined.
Saved Instruction Pointer
The saved contents of CS and EIP registers generally point to the instruction that generated the exception. If the
page-fault exception occurred during a task switch, the CS and EIP registers may point to the first instruction of the
new task (as described in the following “Program State Change” section).
Program State Change
A program-state change does not normally accompany a page-fault exception, because the instruction that causes
the exception to be generated is not executed. After the page-fault exception handler has corrected the violation
(for example, loaded the missing page into memory), execution of the program or task can be resumed.
When a page-fault exception is generated during a task switch, the program-state may change, as follows. During
a task switch, a page-fault exception can occur during any of following operations:
•
•
•
•
•
While writing the state of the original task into the TSS of that task.
While reading the GDT to locate the TSS descriptor of the new task.
While reading the TSS of the new task.
While reading segment descriptors associated with segment selectors from the new task.
While reading the LDT of the new task to verify the segment registers stored in the new TSS.
In the last two cases the exception occurs in the context of the new task. The instruction pointer refers to the first
instruction of the new task, not to the instruction which caused the task switch (or the last instruction to be
1. Processors update CR2 whenever a page fault is detected. If a second page fault occurs while an earlier page fault is being delivered, the faulting linear address of the second fault will overwrite the contents of CR2 (replacing the previous address). These
updates to CR2 occur even if the page fault results in a double fault or occurs during the delivery of a double fault.
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executed, in the case of an interrupt). If the design of the operating system permits page faults to occur during
task-switches, the page-fault handler should be called through a task gate.
If a page fault occurs during a task switch, the processor will load all the state information from the new TSS
(without performing any additional limit, present, or type checks) before it generates the exception. The page-fault
handler should thus not rely on being able to use the segment selectors found in the CS, SS, DS, ES, FS, and GS
registers without causing another exception. (See the Program State Change description for “Interrupt 10—Invalid
TSS Exception (#TS)” in this chapter for additional information on how to handle this situation.)
Additional Exception-Handling Information
Special care should be taken to ensure that an exception that occurs during an explicit stack switch does not cause
the processor to use an invalid stack pointer (SS:ESP). Software written for 16-bit IA-32 processors often use a
pair of instructions to change to a new stack, for example:
MOV SS, AX
MOV SP, StackTop
When executing this code on one of the 32-bit IA-32 processors, it is possible to get a page fault, general-protection fault (#GP), or alignment check fault (#AC) after the segment selector has been loaded into the SS register
but before the ESP register has been loaded. At this point, the two parts of the stack pointer (SS and ESP) are
inconsistent. The new stack segment is being used with the old stack pointer.
The processor does not use the inconsistent stack pointer if the exception handler switches to a well defined stack
(that is, the handler is a task or a more privileged procedure). However, if the exception handler is called at the
same privilege level and from the same task, the processor will attempt to use the inconsistent stack pointer.
In systems that handle page-fault, general-protection, or alignment check exceptions within the faulting task (with
trap or interrupt gates), software executing at the same privilege level as the exception handler should initialize a
new stack by using the LSS instruction rather than a pair of MOV instructions, as described earlier in this note.
When the exception handler is running at privilege level 0 (the normal case), the problem is limited to procedures
or tasks that run at privilege level 0, typically the kernel of the operating system.
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Interrupt 16—x87 FPU Floating-Point Error (#MF)
Exception Class
Fault.
Description
Indicates that the x87 FPU has detected a floating-point error. The NE flag in the register CR0 must be set for an
interrupt 16 (floating-point error exception) to be generated. (See Section 2.5, “Control Registers,” for a detailed
description of the NE flag.)
NOTE
SIMD floating-point exceptions (#XM) are signaled through interrupt 19.
While executing x87 FPU instructions, the x87 FPU detects and reports six types of floating-point error conditions:
•
Invalid operation (#I)
— Stack overflow or underflow (#IS)
— Invalid arithmetic operation (#IA)
•
•
•
•
•
Divide-by-zero (#Z)
Denormalized operand (#D)
Numeric overflow (#O)
Numeric underflow (#U)
Inexact result (precision) (#P)
Each of these error conditions represents an x87 FPU exception type, and for each of exception type, the x87 FPU
provides a flag in the x87 FPU status register and a mask bit in the x87 FPU control register. If the x87 FPU detects
a floating-point error and the mask bit for the exception type is set, the x87 FPU handles the exception automatically by generating a predefined (default) response and continuing program execution. The default responses have
been designed to provide a reasonable result for most floating-point applications.
If the mask for the exception is clear and the NE flag in register CR0 is set, the x87 FPU does the following:
1. Sets the necessary flag in the FPU status register.
2. Waits until the next “waiting” x87 FPU instruction or WAIT/FWAIT instruction is encountered in the program’s
instruction stream.
3. Generates an internal error signal that cause the processor to generate a floating-point exception (#MF).
Prior to executing a waiting x87 FPU instruction or the WAIT/FWAIT instruction, the x87 FPU checks for pending
x87 FPU floating-point exceptions (as described in step 2 above). Pending x87 FPU floating-point exceptions are
ignored for “non-waiting” x87 FPU instructions, which include the FNINIT, FNCLEX, FNSTSW, FNSTSW AX, FNSTCW,
FNSTENV, and FNSAVE instructions. Pending x87 FPU exceptions are also ignored when executing the state
management instructions FXSAVE and FXRSTOR.
All of the x87 FPU floating-point error conditions can be recovered from. The x87 FPU floating-point-error exception
handler can determine the error condition that caused the exception from the settings of the flags in the x87 FPU
status word. See “Software Exception Handling” in Chapter 8 of the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 1, for more information on handling x87 FPU floating-point exceptions.
Exception Error Code
None. The x87 FPU provides its own error information.
Saved Instruction Pointer
The saved contents of CS and EIP registers point to the floating-point or WAIT/FWAIT instruction that was about to
be executed when the floating-point-error exception was generated. This is not the faulting instruction in which the
error condition was detected. The address of the faulting instruction is contained in the x87 FPU instruction pointer
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register. See “x87 FPU Instruction and Operand (Data) Pointers” in Chapter 8 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, for more information about information the FPU saves for use in
handling floating-point-error exceptions.
Program State Change
A program-state change generally accompanies an x87 FPU floating-point exception because the handling of the
exception is delayed until the next waiting x87 FPU floating-point or WAIT/FWAIT instruction following the faulting
instruction. The x87 FPU, however, saves sufficient information about the error condition to allow recovery from the
error and re-execution of the faulting instruction if needed.
In situations where non- x87 FPU floating-point instructions depend on the results of an x87 FPU floating-point
instruction, a WAIT or FWAIT instruction can be inserted in front of a dependent instruction to force a pending x87
FPU floating-point exception to be handled before the dependent instruction is executed. See “x87 FPU Exception
Synchronization” in Chapter 8 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1,
for more information about synchronization of x87 floating-point-error exceptions.
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Interrupt 17—Alignment Check Exception (#AC)
Exception Class
Fault.
Description
Indicates that the processor detected an unaligned memory operand when alignment checking was enabled. Alignment checks are only carried out in data (or stack) accesses (not in code fetches or system segment accesses). An
example of an alignment-check violation is a word stored at an odd byte address, or a doubleword stored at an
address that is not an integer multiple of 4. Table 6-7 lists the alignment requirements various data types recognized by the processor.
Table 6-7. Alignment Requirements by Data Type
Data Type
Address Must Be Divisible By
Word
2
Doubleword
4
Single-precision floating-point (32-bits)
4
Double-precision floating-point (64-bits)
8
Double extended-precision floating-point (80-bits)
8
Quadword
8
Double quadword
16
Segment Selector
2
32-bit Far Pointer
2
48-bit Far Pointer
4
32-bit Pointer
4
GDTR, IDTR, LDTR, or Task Register Contents
4
FSTENV/FLDENV Save Area
4 or 2, depending on operand size
FSAVE/FRSTOR Save Area
4 or 2, depending on operand size
Bit String
2 or 4 depending on the operand-size attribute.
Note that the alignment check exception (#AC) is generated only for data types that must be aligned on word,
doubleword, and quadword boundaries. A general-protection exception (#GP) is generated 128-bit data types that
are not aligned on a 16-byte boundary.
To enable alignment checking, the following conditions must be true:
•
•
•
AM flag in CR0 register is set.
AC flag in the EFLAGS register is set.
The CPL is 3 (protected mode or virtual-8086 mode).
Alignment-check exceptions (#AC) are generated only when operating at privilege level 3 (user mode). Memory
references that default to privilege level 0, such as segment descriptor loads, do not generate alignment-check
exceptions, even when caused by a memory reference made from privilege level 3.
Storing the contents of the GDTR, IDTR, LDTR, or task register in memory while at privilege level 3 can generate
an alignment-check exception. Although application programs do not normally store these registers, the fault can
be avoided by aligning the information stored on an even word-address.
The FXSAVE/XSAVE and FXRSTOR/XRSTOR instructions save and restore a 512-byte data structure, the first byte
of which must be aligned on a 16-byte boundary. If the alignment-check exception (#AC) is enabled when
executing these instructions (and CPL is 3), a misaligned memory operand can cause either an alignment-check
exception or a general-protection exception (#GP) depending on the processor implementation (see “FXSAVESave x87 FPU, MMX, SSE, and SSE2 State” and “FXRSTOR-Restore x87 FPU, MMX, SSE, and SSE2 State” in
Vol. 3A 6-45
INTERRUPT AND EXCEPTION HANDLING
Chapter 3 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A; see “XSAVE—Save
Processor Extended States” and “XRSTOR—Restore Processor Extended States” in Chapter 4 of the Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 2B).
The MOVDQU, MOVUPS, and MOVUPD instructions perform 128-bit unaligned loads or stores. The LDDQU instructions loads 128-bit unaligned data.They do not generate general-protection exceptions (#GP) when operands are
not aligned on a 16-byte boundary. If alignment checking is enabled, alignment-check exceptions (#AC) may or
may not be generated depending on processor implementation when data addresses are not aligned on an 8-byte
boundary.
FSAVE and FRSTOR instructions can generate unaligned references, which can cause alignment-check faults. These
instructions are rarely needed by application programs.
Exception Error Code
Yes. The error code is null; all bits are clear except possibly bit 0 — EXT; see Section 6.13. EXT is set if the #AC is
recognized during delivery of an event other than a software interrupt (see “INT n/INTO/INT 3—Call to Interrupt
Procedure” in Chapter 3 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A).
Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction that generated the exception.
Program State Change
A program-state change does not accompany an alignment-check fault, because the instruction is not executed.
6-46 Vol. 3A
INTERRUPT AND EXCEPTION HANDLING
Interrupt 18—Machine-Check Exception (#MC)
Exception Class
Abort.
Description
Indicates that the processor detected an internal machine error or a bus error, or that an external agent detected
a bus error. The machine-check exception is model-specific, available on the Pentium and later generations of
processors. The implementation of the machine-check exception is different between different processor families,
and these implementations may not be compatible with future Intel 64 or IA-32 processors. (Use the CPUID
instruction to determine whether this feature is present.)
Bus errors detected by external agents are signaled to the processor on dedicated pins: the BINIT# and MCERR#
pins on the Pentium 4, Intel Xeon, and P6 family processors and the BUSCHK# pin on the Pentium processor. When
one of these pins is enabled, asserting the pin causes error information to be loaded into machine-check registers
and a machine-check exception is generated.
The machine-check exception and machine-check architecture are discussed in detail in Chapter 15, “MachineCheck Architecture.” Also, see the data books for the individual processors for processor-specific hardware information.
Exception Error Code
None. Error information is provide by machine-check MSRs.
Saved Instruction Pointer
For the Pentium 4 and Intel Xeon processors, the saved contents of extended machine-check state registers are
directly associated with the error that caused the machine-check exception to be generated (see Section 15.3.1.2,
“IA32_MCG_STATUS MSR,” and Section 15.3.2.6, “IA32_MCG Extended Machine Check State MSRs”).
For the P6 family processors, if the EIPV flag in the MCG_STATUS MSR is set, the saved contents of CS and EIP
registers are directly associated with the error that caused the machine-check exception to be generated; if the
flag is clear, the saved instruction pointer may not be associated with the error (see Section 15.3.1.2,
“IA32_MCG_STATUS MSR”).
For the Pentium processor, contents of the CS and EIP registers may not be associated with the error.
Program State Change
The machine-check mechanism is enabled by setting the MCE flag in control register CR4.
For the Pentium 4, Intel Xeon, P6 family, and Pentium processors, a program-state change always accompanies a
machine-check exception, and an abort class exception is generated. For abort exceptions, information about the
exception can be collected from the machine-check MSRs, but the program cannot generally be restarted.
If the machine-check mechanism is not enabled (the MCE flag in control register CR4 is clear), a machine-check
exception causes the processor to enter the shutdown state.
Vol. 3A 6-47
INTERRUPT AND EXCEPTION HANDLING
Interrupt 19—SIMD Floating-Point Exception (#XM)
Exception Class
Fault.
Description
Indicates the processor has detected an SSE/SSE2/SSE3 SIMD floating-point exception. The appropriate status
flag in the MXCSR register must be set and the particular exception unmasked for this interrupt to be generated.
There are six classes of numeric exception conditions that can occur while executing an SSE/ SSE2/SSE3 SIMD
floating-point instruction:
•
•
•
•
•
•
Invalid operation (#I)
Divide-by-zero (#Z)
Denormal operand (#D)
Numeric overflow (#O)
Numeric underflow (#U)
Inexact result (Precision) (#P)
The invalid operation, divide-by-zero, and denormal-operand exceptions are pre-computation exceptions; that is,
they are detected before any arithmetic operation occurs. The numeric underflow, numeric overflow, and inexact
result exceptions are post-computational exceptions.
See “SIMD Floating-Point Exceptions” in Chapter 11 of the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 1, for additional information about the SIMD floating-point exception classes.
When a SIMD floating-point exception occurs, the processor does either of the following things:
•
It handles the exception automatically by producing the most reasonable result and allowing program
execution to continue undisturbed. This is the response to masked exceptions.
•
It generates a SIMD floating-point exception, which in turn invokes a software exception handler. This is the
response to unmasked exceptions.
Each of the six SIMD floating-point exception conditions has a corresponding flag bit and mask bit in the MXCSR
register. If an exception is masked (the corresponding mask bit in the MXCSR register is set), the processor takes
an appropriate automatic default action and continues with the computation. If the exception is unmasked (the
corresponding mask bit is clear) and the operating system supports SIMD floating-point exceptions (the OSXMMEXCPT flag in control register CR4 is set), a software exception handler is invoked through a SIMD floating-point
exception. If the exception is unmasked and the OSXMMEXCPT bit is clear (indicating that the operating system
does not support unmasked SIMD floating-point exceptions), an invalid opcode exception (#UD) is signaled instead
of a SIMD floating-point exception.
Note that because SIMD floating-point exceptions are precise and occur immediately, the situation does not arise
where an x87 FPU instruction, a WAIT/FWAIT instruction, or another SSE/SSE2/SSE3 instruction will catch a
pending unmasked SIMD floating-point exception.
In situations where a SIMD floating-point exception occurred while the SIMD floating-point exceptions were
masked (causing the corresponding exception flag to be set) and the SIMD floating-point exception was subsequently unmasked, then no exception is generated when the exception is unmasked.
When SSE/SSE2/SSE3 SIMD floating-point instructions operate on packed operands (made up of two or four suboperands), multiple SIMD floating-point exception conditions may be detected. If no more than one exception
condition is detected for one or more sets of sub-operands, the exception flags are set for each exception condition
detected. For example, an invalid exception detected for one sub-operand will not prevent the reporting of a divideby-zero exception for another sub-operand. However, when two or more exceptions conditions are generated for
one sub-operand, only one exception condition is reported, according to the precedences shown in Table 6-8. This
exception precedence sometimes results in the higher priority exception condition being reported and the lower
priority exception conditions being ignored.
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INTERRUPT AND EXCEPTION HANDLING
Table 6-8. SIMD Floating-Point Exceptions Priority
Priority
Description
1 (Highest)
Invalid operation exception due to SNaN operand (or any NaN operand for maximum, minimum, or certain compare and
convert operations).
2
QNaN operand1.
3
Any other invalid operation exception not mentioned above or a divide-by-zero exception2.
4
Denormal operand exception2.
5
Numeric overflow and underflow exceptions possibly in conjunction with the inexact result exception2.
6 (Lowest)
Inexact result exception.
NOTES:
1. Though a QNaN this is not an exception, the handling of a QNaN operand has precedence over lower priority exceptions. For example, a QNaN divided by zero results in a QNaN, not a divide-by-zero- exception.
2. If masked, then instruction execution continues, and a lower priority exception can occur as well.
Exception Error Code
None.
Saved Instruction Pointer
The saved contents of CS and EIP registers point to the SSE/SSE2/SSE3 instruction that was executed when the
SIMD floating-point exception was generated. This is the faulting instruction in which the error condition was
detected.
Program State Change
A program-state change does not accompany a SIMD floating-point exception because the handling of the exception is immediate unless the particular exception is masked. The available state information is often sufficient to
allow recovery from the error and re-execution of the faulting instruction if needed.
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INTERRUPT AND EXCEPTION HANDLING
Interrupt 20—Virtualization Exception (#VE)
Exception Class
Fault.
Description
Indicates that the processor detected an EPT violation in VMX non-root operation. Not all EPT violations cause virtualization exceptions. See Section 25.5.6.2 for details.
The exception handler can recover from EPT violations and restart the program or task without any loss of program
continuity. In some cases, however, the problem that caused the EPT violation may be uncorrectable.
Exception Error Code
None.
Saved Instruction Pointer
The saved contents of CS and EIP registers generally point to the instruction that generated the exception.
Program State Change
A program-state change does not normally accompany a virtualization exception, because the instruction that
causes the exception to be generated is not executed. After the virtualization exception handler has corrected the
violation (for example, by executing the EPTP-switching VM function), execution of the program or task can be
resumed.
Additional Exception-Handling Information
The processor saves information about virtualization exceptions in the virtualization-exception information area.
See Section 25.5.6.2 for details.
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INTERRUPT AND EXCEPTION HANDLING
Interrupts 32 to 255—User Defined Interrupts
Exception Class
Not applicable.
Description
Indicates that the processor did one of the following things:
•
•
Executed an INT n instruction where the instruction operand is one of the vector numbers from 32 through 255.
Responded to an interrupt request at the INTR pin or from the local APIC when the interrupt vector number
associated with the request is from 32 through 255.
Exception Error Code
Not applicable.
Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction that follows the INT n instruction or instruction
following the instruction on which the INTR signal occurred.
Program State Change
A program-state change does not accompany interrupts generated by the INT n instruction or the INTR signal. The
INT n instruction generates the interrupt within the instruction stream. When the processor receives an INTR
signal, it commits all state changes for all previous instructions before it responds to the interrupt; so, program
execution can resume upon returning from the interrupt handler.
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INTERRUPT AND EXCEPTION HANDLING
6-52 Vol. 3A
CHAPTER 7
TASK MANAGEMENT
This chapter describes the IA-32 architecture’s task management facilities. These facilities are only available when
the processor is running in protected mode.
This chapter focuses on 32-bit tasks and the 32-bit TSS structure. For information on 16-bit tasks and the 16-bit
TSS structure, see Section 7.6, “16-Bit Task-State Segment (TSS).” For information specific to task management in
64-bit mode, see Section 7.7, “Task Management in 64-bit Mode.”
7.1
TASK MANAGEMENT OVERVIEW
A task is a unit of work that a processor can dispatch, execute, and suspend. It can be used to execute a program,
a task or process, an operating-system service utility, an interrupt or exception handler, or a kernel or executive
utility.
The IA-32 architecture provides a mechanism for saving the state of a task, for dispatching tasks for execution, and
for switching from one task to another. When operating in protected mode, all processor execution takes place from
within a task. Even simple systems must define at least one task. More complex systems can use the processor’s
task management facilities to support multitasking applications.
7.1.1
Task Structure
A task is made up of two parts: a task execution space and a task-state segment (TSS). The task execution space
consists of a code segment, a stack segment, and one or more data segments (see Figure 7-1). If an operating
system or executive uses the processor’s privilege-level protection mechanism, the task execution space also
provides a separate stack for each privilege level.
The TSS specifies the segments that make up the task execution space and provides a storage place for task state
information. In multitasking systems, the TSS also provides a mechanism for linking tasks.
A task is identified by the segment selector for its TSS. When a task is loaded into the processor for execution, the
segment selector, base address, limit, and segment descriptor attributes for the TSS are loaded into the task
register (see Section 2.4.4, “Task Register (TR)”).
If paging is implemented for the task, the base address of the page directory used by the task is loaded into control
register CR3.
Vol. 3A 7-1
TASK MANAGEMENT
Code
Segment
Data
Segment
Task-State
Segment
(TSS)
Stack
Segment
(Current Priv.
Level)
Stack Seg.
Priv. Level 0
Stack Seg.
Priv. Level 1
Task Register
CR3
Stack
Segment
(Priv. Level 2)
Figure 7-1. Structure of a Task
7.1.2
Task State
The following items define the state of the currently executing task:
•
The task’s current execution space, defined by the segment selectors in the segment registers (CS, DS, SS, ES,
FS, and GS).
•
•
•
•
•
•
•
•
•
The state of the general-purpose registers.
The state of the EFLAGS register.
The state of the EIP register.
The state of control register CR3.
The state of the task register.
The state of the LDTR register.
The I/O map base address and I/O map (contained in the TSS).
Stack pointers to the privilege 0, 1, and 2 stacks (contained in the TSS).
Link to previously executed task (contained in the TSS).
Prior to dispatching a task, all of these items are contained in the task’s TSS, except the state of the task register.
Also, the complete contents of the LDTR register are not contained in the TSS, only the segment selector for the
LDT.
7.1.3
Executing a Task
Software or the processor can dispatch a task for execution in one of the following ways:
•
•
•
•
•
A explicit call to a task with the CALL instruction.
A explicit jump to a task with the JMP instruction.
An implicit call (by the processor) to an interrupt-handler task.
An implicit call to an exception-handler task.
A return (initiated with an IRET instruction) when the NT flag in the EFLAGS register is set.
All of these methods for dispatching a task identify the task to be dispatched with a segment selector that points to
a task gate or the TSS for the task. When dispatching a task with a CALL or JMP instruction, the selector in the
instruction may select the TSS directly or a task gate that holds the selector for the TSS. When dispatching a task
7-2 Vol. 3A
TASK MANAGEMENT
to handle an interrupt or exception, the IDT entry for the interrupt or exception must contain a task gate that holds
the selector for the interrupt- or exception-handler TSS.
When a task is dispatched for execution, a task switch occurs between the currently running task and the
dispatched task. During a task switch, the execution environment of the currently executing task (called the task’s
state or context) is saved in its TSS and execution of the task is suspended. The context for the dispatched task is
then loaded into the processor and execution of that task begins with the instruction pointed to by the newly loaded
EIP register. If the task has not been run since the system was last initialized, the EIP will point to the first instruction of the task’s code; otherwise, it will point to the next instruction after the last instruction that the task
executed when it was last active.
If the currently executing task (the calling task) called the task being dispatched (the called task), the TSS
segment selector for the calling task is stored in the TSS of the called task to provide a link back to the calling task.
For all IA-32 processors, tasks are not recursive. A task cannot call or jump to itself.
Interrupts and exceptions can be handled with a task switch to a handler task. Here, the processor performs a task
switch to handle the interrupt or exception and automatically switches back to the interrupted task upon returning
from the interrupt-handler task or exception-handler task. This mechanism can also handle interrupts that occur
during interrupt tasks.
As part of a task switch, the processor can also switch to another LDT, allowing each task to have a different logicalto-physical address mapping for LDT-based segments. The page-directory base register (CR3) also is reloaded on a
task switch, allowing each task to have its own set of page tables. These protection facilities help isolate tasks and
prevent them from interfering with one another.
If protection mechanisms are not used, the processor provides no protection between tasks. This is true even with
operating systems that use multiple privilege levels for protection. A task running at privilege level 3 that uses the
same LDT and page tables as other privilege-level-3 tasks can access code and corrupt data and the stack of other
tasks.
Use of task management facilities for handling multitasking applications is optional. Multitasking can be handled in
software, with each software defined task executed in the context of a single IA-32 architecture task.
7.2
TASK MANAGEMENT DATA STRUCTURES
The processor defines five data structures for handling task-related activities:
•
•
•
•
•
Task-state segment (TSS).
Task-gate descriptor.
TSS descriptor.
Task register.
NT flag in the EFLAGS register.
When operating in protected mode, a TSS and TSS descriptor must be created for at least one task, and the
segment selector for the TSS must be loaded into the task register (using the LTR instruction).
7.2.1
Task-State Segment (TSS)
The processor state information needed to restore a task is saved in a system segment called the task-state
segment (TSS). Figure 7-2 shows the format of a TSS for tasks designed for 32-bit CPUs. The fields of a TSS are
divided into two main categories: dynamic fields and static fields.
For information about 16-bit Intel 286 processor task structures, see Section 7.6, “16-Bit Task-State Segment
(TSS).” For information about 64-bit mode task structures, see Section 7.7, “Task Management in 64-bit Mode.”
Vol. 3A 7-3
TASK MANAGEMENT
31
0
15
Reserved
I/O Map Base Address
T 100
LDT Segment Selector
Reserved
96
Reserved
GS
92
Reserved
FS
88
Reserved
DS
84
Reserved
SS
80
Reserved
CS
76
Reserved
ES
72
EDI
68
ESI
64
EBP
60
ESP
56
EBX
52
EDX
48
ECX
44
EAX
40
EFLAGS
36
EIP
32
CR3 (PDBR)
28
Reserved
SS2
Reserved
SS1
SS0
8
4
ESP0
Reserved
16
12
ESP1
Reserved
24
20
ESP2
Previous Task Link
0
Reserved bits. Set to 0.
Figure 7-2. 32-Bit Task-State Segment (TSS)
The processor updates dynamic fields when a task is suspended during a task switch. The following are dynamic
fields:
•
General-purpose register fields — State of the EAX, ECX, EDX, EBX, ESP, EBP, ESI, and EDI registers prior
to the task switch.
•
Segment selector fields — Segment selectors stored in the ES, CS, SS, DS, FS, and GS registers prior to the
task switch.
•
•
•
EFLAGS register field — State of the EFAGS register prior to the task switch.
EIP (instruction pointer) field — State of the EIP register prior to the task switch.
Previous task link field — Contains the segment selector for the TSS of the previous task (updated on a task
switch that was initiated by a call, interrupt, or exception). This field (which is sometimes called the back link
field) permits a task switch back to the previous task by using the IRET instruction.
The processor reads the static fields, but does not normally change them. These fields are set up when a task is
created. The following are static fields:
•
LDT segment selector field — Contains the segment selector for the task's LDT.
7-4 Vol. 3A
TASK MANAGEMENT
•
CR3 control register field — Contains the base physical address of the page directory to be used by the task.
Control register CR3 is also known as the page-directory base register (PDBR).
•
Privilege level-0, -1, and -2 stack pointer fields — These stack pointers consist of a logical address made
up of the segment selector for the stack segment (SS0, SS1, and SS2) and an offset into the stack (ESP0,
ESP1, and ESP2). Note that the values in these fields are static for a particular task; whereas, the SS and ESP
values will change if stack switching occurs within the task.
•
T (debug trap) flag (byte 100, bit 0) — When set, the T flag causes the processor to raise a debug exception
when a task switch to this task occurs (see Section 17.3.1.5, “Task-Switch Exception Condition”).
•
I/O map base address field — Contains a 16-bit offset from the base of the TSS to the I/O permission bit
map and interrupt redirection bitmap. When present, these maps are stored in the TSS at higher addresses.
The I/O map base address points to the beginning of the I/O permission bit map and the end of the interrupt
redirection bit map. See Chapter 14, “Input/Output,” in the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 1, for more information about the I/O permission bit map. See Section 20.3,
“Interrupt and Exception Handling in Virtual-8086 Mode,” for a detailed description of the interrupt redirection
bit map.
If paging is used:
•
Avoid placing a page boundary in the part of the TSS that the processor reads during a task switch (the first 104
bytes). The processor may not correctly perform address translations if a boundary occurs in this area. During
a task switch, the processor reads and writes into the first 104 bytes of each TSS (using contiguous physical
addresses beginning with the physical address of the first byte of the TSS). So, after TSS access begins, if part
of the 104 bytes is not physically contiguous, the processor will access incorrect information without generating
a page-fault exception.
•
Pages corresponding to the previous task’s TSS, the current task’s TSS, and the descriptor table entries for
each all should be marked as read/write.
•
Task switches are carried out faster if the pages containing these structures are present in memory before the
task switch is initiated.
7.2.2
TSS Descriptor
The TSS, like all other segments, is defined by a segment descriptor. Figure 7-3 shows the format of a TSS
descriptor. TSS descriptors may only be placed in the GDT; they cannot be placed in an LDT or the IDT.
An attempt to access a TSS using a segment selector with its TI flag set (which indicates the current LDT) causes
a general-protection exception (#GP) to be generated during CALLs and JMPs; it causes an invalid TSS exception
(#TS) during IRETs. A general-protection exception is also generated if an attempt is made to load a segment
selector for a TSS into a segment register.
The busy flag (B) in the type field indicates whether the task is busy. A busy task is currently running or suspended.
A type field with a value of 1001B indicates an inactive task; a value of 1011B indicates a busy task. Tasks are not
recursive. The processor uses the busy flag to detect an attempt to call a task whose execution has been interrupted. To insure that there is only one busy flag is associated with a task, each TSS should have only one TSS
descriptor that points to it.
Vol. 3A 7-5
TASK MANAGEMENT
TSS Descriptor
31
24 23 22 21 20 19
Base 31:24
A
G 0 0 V
L
31
16 15 14 13 12 11
Limit
19:16
P
D
P
L
0
8 7
Type
16 15
Base Address 15:00
AVL
B
BASE
DPL
G
LIMIT
P
TYPE
4
Base 23:16
0 1 0 B 1
0
Segment Limit 15:00
0
Available for use by system software
Busy flag
Segment Base Address
Descriptor Privilege Level
Granularity
Segment Limit
Segment Present
Segment Type
Figure 7-3. TSS Descriptor
The base, limit, and DPL fields and the granularity and present flags have functions similar to their use in datasegment descriptors (see Section 3.4.5, “Segment Descriptors”). When the G flag is 0 in a TSS descriptor for a 32bit TSS, the limit field must have a value equal to or greater than 67H, one byte less than the minimum size of a
TSS. Attempting to switch to a task whose TSS descriptor has a limit less than 67H generates an invalid-TSS exception (#TS). A larger limit is required if an I/O permission bit map is included or if the operating system stores additional data. The processor does not check for a limit greater than 67H on a task switch; however, it does check
when accessing the I/O permission bit map or interrupt redirection bit map.
Any program or procedure with access to a TSS descriptor (that is, whose CPL is numerically equal to or less than
the DPL of the TSS descriptor) can dispatch the task with a call or a jump.
In most systems, the DPLs of TSS descriptors are set to values less than 3, so that only privileged software can
perform task switching. However, in multitasking applications, DPLs for some TSS descriptors may be set to 3 to
allow task switching at the application (or user) privilege level.
7.2.3
TSS Descriptor in 64-bit mode
In 64-bit mode, task switching is not supported, but TSS descriptors still exist. The format of a 64-bit TSS is
described in Section 7.7.
In 64-bit mode, the TSS descriptor is expanded to 16 bytes (see Figure 7-4). This expansion also applies to an LDT
descriptor in 64-bit mode. Table 3-2 provides the encoding information for the segment type field.
7-6 Vol. 3A
TASK MANAGEMENT
TSS (or LDT) Descriptor
31
13 12
Reserved
0
8 7
0
12
Reserved
31
0
8
Base Address 63:32
31
24 23 22 21 20 19
Base 31:24
A
G 0 0 V
L
31
16 15 14 13 12 11
Limit
19:16
P
D
P
L
0
8 7
Type
16 15
Base Address 15:00
AVL
B
BASE
DPL
G
LIMIT
P
TYPE
4
Base 23:16
0
0
Segment Limit 15:00
0
Available for use by system software
Busy flag
Segment Base Address
Descriptor Privilege Level
Granularity
Segment Limit
Segment Present
Segment Type
Figure 7-4. Format of TSS and LDT Descriptors in 64-bit Mode
7.2.4
Task Register
The task register holds the 16-bit segment selector and the entire segment descriptor (32-bit base address (64 bits
in IA-32e mode), 16-bit segment limit, and descriptor attributes) for the TSS of the current task (see Figure 2-6).
This information is copied from the TSS descriptor in the GDT for the current task. Figure 7-5 shows the path the
processor uses to access the TSS (using the information in the task register).
The task register has a visible part (that can be read and changed by software) and an invisible part (maintained
by the processor and is inaccessible by software). The segment selector in the visible portion points to a TSS
descriptor in the GDT. The processor uses the invisible portion of the task register to cache the segment descriptor
for the TSS. Caching these values in a register makes execution of the task more efficient. The LTR (load task
register) and STR (store task register) instructions load and read the visible portion of the task register:
The LTR instruction loads a segment selector (source operand) into the task register that points to a TSS descriptor
in the GDT. It then loads the invisible portion of the task register with information from the TSS descriptor. LTR is a
privileged instruction that may be executed only when the CPL is 0. It’s used during system initialization to put an
initial value in the task register. Afterwards, the contents of the task register are changed implicitly when a task
switch occurs.
The STR (store task register) instruction stores the visible portion of the task register in a general-purpose register
or memory. This instruction can be executed by code running at any privilege level in order to identify the currently
running task. However, it is normally used only by operating system software.
On power up or reset of the processor, segment selector and base address are set to the default value of 0; the limit
is set to FFFFH.
Vol. 3A 7-7
TASK MANAGEMENT
TSS
+
Visible Part
Task
Register
Selector
Invisible Part
Base Address
Segment Limit
GDT
TSS Descriptor
0
Figure 7-5. Task Register
7.2.5
Task-Gate Descriptor
A task-gate descriptor provides an indirect, protected reference to a task (see Figure 7-6). It can be placed in the
GDT, an LDT, or the IDT. The TSS segment selector field in a task-gate descriptor points to a TSS descriptor in the
GDT. The RPL in this segment selector is not used.
The DPL of a task-gate descriptor controls access to the TSS descriptor during a task switch. When a program or
procedure makes a call or jump to a task through a task gate, the CPL and the RPL field of the gate selector pointing
to the task gate must be less than or equal to the DPL of the task-gate descriptor. Note that when a task gate is
used, the DPL of the destination TSS descriptor is not used.
31
16 15 14 13 12 11
Reserved
31
P
D
P
L
Type
DPL
P
TYPE
4
0
Reserved
Descriptor Privilege Level
Segment Present
Segment Type
Figure 7-6. Task-Gate Descriptor
7-8 Vol. 3A
Reserved
0 0 1 0 1
16 15
TSS Segment Selector
0
8 7
0
TASK MANAGEMENT
A task can be accessed either through a task-gate descriptor or a TSS descriptor. Both of these structures satisfy
the following needs:
•
Need for a task to have only one busy flag — Because the busy flag for a task is stored in the TSS
descriptor, each task should have only one TSS descriptor. There may, however, be several task gates that
reference the same TSS descriptor.
•
Need to provide selective access to tasks — Task gates fill this need, because they can reside in an LDT and
can have a DPL that is different from the TSS descriptor's DPL. A program or procedure that does not have
sufficient privilege to access the TSS descriptor for a task in the GDT (which usually has a DPL of 0) may be
allowed access to the task through a task gate with a higher DPL. Task gates give the operating system greater
latitude for limiting access to specific tasks.
•
Need for an interrupt or exception to be handled by an independent task — Task gates may also reside
in the IDT, which allows interrupts and exceptions to be handled by handler tasks. When an interrupt or
exception vector points to a task gate, the processor switches to the specified task.
Figure 7-7 illustrates how a task gate in an LDT, a task gate in the GDT, and a task gate in the IDT can all point to
the same task.
LDT
GDT
TSS
Task Gate
Task Gate
TSS Descriptor
IDT
Task Gate
Figure 7-7. Task Gates Referencing the Same Task
7.3
TASK SWITCHING
The processor transfers execution to another task in one of four cases:
•
•
The current program, task, or procedure executes a JMP or CALL instruction to a TSS descriptor in the GDT.
The current program, task, or procedure executes a JMP or CALL instruction to a task-gate descriptor in the
GDT or the current LDT.
Vol. 3A 7-9
TASK MANAGEMENT
•
•
An interrupt or exception vector points to a task-gate descriptor in the IDT.
The current task executes an IRET when the NT flag in the EFLAGS register is set.
JMP, CALL, and IRET instructions, as well as interrupts and exceptions, are all mechanisms for redirecting a
program. The referencing of a TSS descriptor or a task gate (when calling or jumping to a task) or the state of the
NT flag (when executing an IRET instruction) determines whether a task switch occurs.
The processor performs the following operations when switching to a new task:
1. Obtains the TSS segment selector for the new task as the operand of the JMP or CALL instruction, from a task
gate, or from the previous task link field (for a task switch initiated with an IRET instruction).
2. Checks that the current (old) task is allowed to switch to the new task. Data-access privilege rules apply to JMP
and CALL instructions. The CPL of the current (old) task and the RPL of the segment selector for the new task
must be less than or equal to the DPL of the TSS descriptor or task gate being referenced. Exceptions,
interrupts (except for interrupts generated by the INT n instruction), and the IRET instruction are permitted to
switch tasks regardless of the DPL of the destination task-gate or TSS descriptor. For interrupts generated by
the INT n instruction, the DPL is checked.
3. Checks that the TSS descriptor of the new task is marked present and has a valid limit (greater than or equal
to 67H).
4. Checks that the new task is available (call, jump, exception, or interrupt) or busy (IRET return).
5. Checks that the current (old) TSS, new TSS, and all segment descriptors used in the task switch are paged into
system memory.
6. If the task switch was initiated with a JMP or IRET instruction, the processor clears the busy (B) flag in the
current (old) task’s TSS descriptor; if initiated with a CALL instruction, an exception, or an interrupt: the busy
(B) flag is left set. (See Table 7-2.)
7. If the task switch was initiated with an IRET instruction, the processor clears the NT flag in a temporarily saved
image of the EFLAGS register; if initiated with a CALL or JMP instruction, an exception, or an interrupt, the NT
flag is left unchanged in the saved EFLAGS image.
8. Saves the state of the current (old) task in the current task’s TSS. The processor finds the base address of the
current TSS in the task register and then copies the states of the following registers into the current TSS: all the
general-purpose registers, segment selectors from the segment registers, the temporarily saved image of the
EFLAGS register, and the instruction pointer register (EIP).
9. If the task switch was initiated with a CALL instruction, an exception, or an interrupt, the processor will set the
NT flag in the EFLAGS loaded from the new task. If initiated with an IRET instruction or JMP instruction, the NT
flag will reflect the state of NT in the EFLAGS loaded from the new task (see Table 7-2).
10. If the task switch was initiated with a CALL instruction, JMP instruction, an exception, or an interrupt, the
processor sets the busy (B) flag in the new task’s TSS descriptor; if initiated with an IRET instruction, the busy
(B) flag is left set.
11. Loads the task register with the segment selector and descriptor for the new task's TSS.
12. The TSS state is loaded into the processor. This includes the LDTR register, the PDBR (control register CR3), the
EFLAGS register, the EIP register, the general-purpose registers, and the segment selectors. A fault during the
load of this state may corrupt architectural state.
13. The descriptors associated with the segment selectors are loaded and qualified. Any errors associated with this
loading and qualification occur in the context of the new task and may corrupt architectural state.
NOTES
If all checks and saves have been carried out successfully, the processor commits to the task
switch. If an unrecoverable error occurs in steps 1 through 11, the processor does not complete the
task switch and insures that the processor is returned to its state prior to the execution of the
instruction that initiated the task switch.
If an unrecoverable error occurs in step 12, architectural state may be corrupted, but an attempt
will be made to handle the error in the prior execution environment. If an unrecoverable error
occurs after the commit point (in step 13), the processor completes the task switch (without
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TASK MANAGEMENT
performing additional access and segment availability checks) and generates the appropriate
exception prior to beginning execution of the new task.
If exceptions occur after the commit point, the exception handler must finish the task switch itself
before allowing the processor to begin executing the new task. See Chapter 6, “Interrupt
10—Invalid TSS Exception (#TS),” for more information about the affect of exceptions on a task
when they occur after the commit point of a task switch.
14. Begins executing the new task. (To an exception handler, the first instruction of the new task appears not to
have been executed.)
The state of the currently executing task is always saved when a successful task switch occurs. If the task is
resumed, execution starts with the instruction pointed to by the saved EIP value, and the registers are restored to
the values they held when the task was suspended.
When switching tasks, the privilege level of the new task does not inherit its privilege level from the suspended
task. The new task begins executing at the privilege level specified in the CPL field of the CS register, which is
loaded from the TSS. Because tasks are isolated by their separate address spaces and TSSs and because privilege
rules control access to a TSS, software does not need to perform explicit privilege checks on a task switch.
Table 7-1 shows the exception conditions that the processor checks for when switching tasks. It also shows the
exception that is generated for each check if an error is detected and the segment that the error code references.
(The order of the checks in the table is the order used in the P6 family processors. The exact order is model specific
and may be different for other IA-32 processors.) Exception handlers designed to handle these exceptions may be
subject to recursive calls if they attempt to reload the segment selector that generated the exception. The cause of
the exception (or the first of multiple causes) should be fixed before reloading the selector.
Table 7-1. Exception Conditions Checked During a Task Switch
Condition Checked
Exception1
Error Code Reference2
Segment selector for a TSS descriptor references
the GDT and is within the limits of the table.
#GP
New Task’s TSS
TSS descriptor is present in memory.
#NP
TSS descriptor is not busy (for task switch initiated by a call, interrupt, or
exception).
#GP (for JMP, CALL, INT) Task’s back-link TSS
TSS descriptor is not busy (for task switch initiated by an IRET instruction).
#TS (for IRET)
New Task’s TSS
TSS segment limit greater than or equal to 108 (for 32-bit TSS) or 44 (for 16-bit
TSS).
#TS
New Task’s TSS
LDT segment selector of new task is valid 3.
#TS
New Task’s LDT
Code segment DPL matches segment selector RPL.
#TS
New Code Segment
SS segment selector is valid
#TS (for IRET)
New Task’s TSS
Registers are loaded from the values in the TSS.
#TS
New Stack Segment
Stack segment is present in memory.
#SS
New Stack Segment
Stack segment DPL matches CPL.
#TS
New stack segment
LDT of new task is present in memory.
#TS
New Task’s LDT
CS segment selector is valid
#TS
New Code Segment
#NP
New Code Segment
#TS
New Stack Segment
#TS
New Data Segment
#TS
New Data Segment
2.
3.
Code segment is present in memory.
Stack segment DPL matches selector RPL.
DS, ES, FS, and GS segment selectors are valid
DS, ES, FS, and GS segments are readable.
3.
Vol. 3A 7-11
TASK MANAGEMENT
Table 7-1. Exception Conditions Checked During a Task Switch (Contd.)
Condition Checked
Exception1
Error Code Reference2
DS, ES, FS, and GS segments are present in memory.
#NP
New Data Segment
DS, ES, FS, and GS segment DPL greater than or equal to CPL (unless these are
conforming segments).
#TS
New Data Segment
NOTES:
1. #NP is segment-not-present exception, #GP is general-protection exception, #TS is invalid-TSS exception, and #SS is stack-fault
exception.
2. The error code contains an index to the segment descriptor referenced in this column.
3. A segment selector is valid if it is in a compatible type of table (GDT or LDT), occupies an address within the table's segment limit,
and refers to a compatible type of descriptor (for example, a segment selector in the CS register only is valid when it points to a
code-segment descriptor).
The TS (task switched) flag in the control register CR0 is set every time a task switch occurs. System software uses
the TS flag to coordinate the actions of floating-point unit when generating floating-point exceptions with the rest
of the processor. The TS flag indicates that the context of the floating-point unit may be different from that of the
current task. See Section 2.5, “Control Registers”, for a detailed description of the function and use of the TS flag.
7.4
TASK LINKING
The previous task link field of the TSS (sometimes called the “backlink”) and the NT flag in the EFLAGS register are
used to return execution to the previous task. EFLAGS.NT = 1 indicates that the currently executing task is nested
within the execution of another task.
When a CALL instruction, an interrupt, or an exception causes a task switch: the processor copies the segment
selector for the current TSS to the previous task link field of the TSS for the new task; it then sets EFLAGS.NT = 1.
If software uses an IRET instruction to suspend the new task, the processor checks for EFLAGS.NT = 1; it then uses
the value in the previous task link field to return to the previous task. See Figures 7-8.
When a JMP instruction causes a task switch, the new task is not nested. The previous task link field is not used and
EFLAGS.NT = 0. Use a JMP instruction to dispatch a new task when nesting is not desired.
Top Level
Task
Nested
Task
More Deeply
Nested Task
Currently Executing
Task
TSS
TSS
TSS
EFLAGS
NT=1
NT=0
Previous
Task Link
NT=1
Previous
Task Link
NT=1
Previous
Task Link
Task Register
Figure 7-8. Nested Tasks
Table 7-2 shows the busy flag (in the TSS segment descriptor), the NT flag, the previous task link field, and TS flag
(in control register CR0) during a task switch.
The NT flag may be modified by software executing at any privilege level. It is possible for a program to set the NT
flag and execute an IRET instruction. This might randomly invoke the task specified in the previous link field of the
current task's TSS. To keep such spurious task switches from succeeding, the operating system should initialize the
previous task link field in every TSS that it creates to 0.
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TASK MANAGEMENT
Table 7-2. Effect of a Task Switch on Busy Flag, NT Flag, Previous Task Link Field, and TS Flag
Flag or Field
Effect of JMP instruction
Effect of CALL Instruction or
Interrupt
Effect of IRET
Instruction
Busy (B) flag of new task.
Flag is set. Must have been
clear before.
Flag is set. Must have been
clear before.
No change. Must have been set.
Busy flag of old task.
Flag is cleared.
No change. Flag is currently
set.
Flag is cleared.
NT flag of new task.
Set to value from TSS of new
task.
Flag is set.
Set to value from TSS of new
task.
NT flag of old task.
No change.
No change.
Flag is cleared.
Previous task link field of new
task.
No change.
Loaded with selector
for old task’s TSS.
No change.
Previous task link field of old
task.
No change.
No change.
No change.
TS flag in control register CR0.
Flag is set.
Flag is set.
Flag is set.
7.4.1
Use of Busy Flag To Prevent Recursive Task Switching
A TSS allows only one context to be saved for a task; therefore, once a task is called (dispatched), a recursive (or
re-entrant) call to the task would cause the current state of the task to be lost. The busy flag in the TSS segment
descriptor is provided to prevent re-entrant task switching and a subsequent loss of task state information. The
processor manages the busy flag as follows:
1. When dispatching a task, the processor sets the busy flag of the new task.
2. If during a task switch, the current task is placed in a nested chain (the task switch is being generated by a
CALL instruction, an interrupt, or an exception), the busy flag for the current task remains set.
3. When switching to the new task (initiated by a CALL instruction, interrupt, or exception), the processor
generates a general-protection exception (#GP) if the busy flag of the new task is already set. If the task switch
is initiated with an IRET instruction, the exception is not raised because the processor expects the busy flag to
be set.
4. When a task is terminated by a jump to a new task (initiated with a JMP instruction in the task code) or by an
IRET instruction in the task code, the processor clears the busy flag, returning the task to the “not busy” state.
The processor prevents recursive task switching by preventing a task from switching to itself or to any task in a
nested chain of tasks. The chain of nested suspended tasks may grow to any length, due to multiple calls, interrupts, or exceptions. The busy flag prevents a task from being invoked if it is in this chain.
The busy flag may be used in multiprocessor configurations, because the processor follows a LOCK protocol (on the
bus or in the cache) when it sets or clears the busy flag. This lock keeps two processors from invoking the same
task at the same time. See Section 8.1.2.1, “Automatic Locking,” for more information about setting the busy flag
in a multiprocessor applications.
7.4.2
Modifying Task Linkages
In a uniprocessor system, in situations where it is necessary to remove a task from a chain of linked tasks, use the
following procedure to remove the task:
1. Disable interrupts.
2. Change the previous task link field in the TSS of the pre-empting task (the task that suspended the task to be
removed). It is assumed that the pre-empting task is the next task (newer task) in the chain from the task to
be removed. Change the previous task link field to point to the TSS of the next oldest task in the chain or to an
even older task in the chain.
3. Clear the busy (B) flag in the TSS segment descriptor for the task being removed from the chain. If more than
one task is being removed from the chain, the busy flag for each task being remove must be cleared.
Vol. 3A 7-13
TASK MANAGEMENT
4. Enable interrupts.
In a multiprocessing system, additional synchronization and serialization operations must be added to this procedure to insure that the TSS and its segment descriptor are both locked when the previous task link field is changed
and the busy flag is cleared.
7.5
TASK ADDRESS SPACE
The address space for a task consists of the segments that the task can access. These segments include the code,
data, stack, and system segments referenced in the TSS and any other segments accessed by the task code. The
segments are mapped into the processor’s linear address space, which is in turn mapped into the processor’s physical address space (either directly or through paging).
The LDT segment field in the TSS can be used to give each task its own LDT. Giving a task its own LDT allows the
task address space to be isolated from other tasks by placing the segment descriptors for all the segments associated with the task in the task’s LDT.
It also is possible for several tasks to use the same LDT. This is a memory-efficient way to allow specific tasks to
communicate with or control each other, without dropping the protection barriers for the entire system.
Because all tasks have access to the GDT, it also is possible to create shared segments accessed through segment
descriptors in this table.
If paging is enabled, the CR3 register (PDBR) field in the TSS allows each task to have its own set of page tables for
mapping linear addresses to physical addresses. Or, several tasks can share the same set of page tables.
7.5.1
Mapping Tasks to the Linear and Physical Address Spaces
Tasks can be mapped to the linear address space and physical address space in one of two ways:
•
One linear-to-physical address space mapping is shared among all tasks. — When paging is not
enabled, this is the only choice. Without paging, all linear addresses map to the same physical addresses. When
paging is enabled, this form of linear-to-physical address space mapping is obtained by using one page
directory for all tasks. The linear address space may exceed the available physical space if demand-paged
virtual memory is supported.
•
Each task has its own linear address space that is mapped to the physical address space. — This form
of mapping is accomplished by using a different page directory for each task. Because the PDBR (control
register CR3) is loaded on task switches, each task may have a different page directory.
The linear address spaces of different tasks may map to completely distinct physical addresses. If the entries of
different page directories point to different page tables and the page tables point to different pages of physical
memory, then the tasks do not share physical addresses.
With either method of mapping task linear address spaces, the TSSs for all tasks must lie in a shared area of the
physical space, which is accessible to all tasks. This mapping is required so that the mapping of TSS addresses does
not change while the processor is reading and updating the TSSs during a task switch. The linear address space
mapped by the GDT also should be mapped to a shared area of the physical space; otherwise, the purpose of the
GDT is defeated. Figure 7-9 shows how the linear address spaces of two tasks can overlap in the physical space by
sharing page tables.
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TASK MANAGEMENT
TSS
Page Directories
Page Tables
Page Frames
Task A
Task A TSS
PDBR
PTE
PTE
PTE
PDE
PDE
Task A
Task A
Shared PT
Shared
PTE
PTE
Task B TSS
Shared
Task B
PDBR
PDE
PDE
PTE
PTE
Task B
Figure 7-9. Overlapping Linear-to-Physical Mappings
7.5.2
Task Logical Address Space
To allow the sharing of data among tasks, use the following techniques to create shared logical-to-physical
address-space mappings for data segments:
•
Through the segment descriptors in the GDT — All tasks must have access to the segment descriptors in
the GDT. If some segment descriptors in the GDT point to segments in the linear-address space that are
mapped into an area of the physical-address space common to all tasks, then all tasks can share the data and
code in those segments.
•
Through a shared LDT — Two or more tasks can use the same LDT if the LDT fields in their TSSs point to the
same LDT. If some segment descriptors in a shared LDT point to segments that are mapped to a common area
of the physical address space, the data and code in those segments can be shared among the tasks that share
the LDT. This method of sharing is more selective than sharing through the GDT, because the sharing can be
limited to specific tasks. Other tasks in the system may have different LDTs that do not give them access to the
shared segments.
•
Through segment descriptors in distinct LDTs that are mapped to common addresses in linear
address space — If this common area of the linear address space is mapped to the same area of the physical
address space for each task, these segment descriptors permit the tasks to share segments. Such segment
descriptors are commonly called aliases. This method of sharing is even more selective than those listed above,
because, other segment descriptors in the LDTs may point to independent linear addresses which are not
shared.
7.6
16-BIT TASK-STATE SEGMENT (TSS)
The 32-bit IA-32 processors also recognize a 16-bit TSS format like the one used in Intel 286 processors (see
Figure 7-10). This format is supported for compatibility with software written to run on earlier IA-32 processors.
The following information is important to know about the 16-bit TSS.
•
•
Do not use a 16-bit TSS to implement a virtual-8086 task.
The valid segment limit for a 16-bit TSS is 2CH.
Vol. 3A 7-15
TASK MANAGEMENT
•
The 16-bit TSS does not contain a field for the base address of the page directory, which is loaded into control
register CR3. A separate set of page tables for each task is not supported for 16-bit tasks. If a 16-bit task is
dispatched, the page-table structure for the previous task is used.
•
•
•
The I/O base address is not included in the 16-bit TSS. None of the functions of the I/O map are supported.
When task state is saved in a 16-bit TSS, the upper 16 bits of the EFLAGS register and the EIP register are lost.
When the general-purpose registers are loaded or saved from a 16-bit TSS, the upper 16 bits of the registers
are modified and not maintained.
15
0
Task LDT Selector
42
DS Selector
40
SS Selector
38
CS Selector
ES Selector
36
34
DI
32
SI
30
BP
28
SP
26
BX
24
DX
22
CX
20
AX
18
FLAG Word
16
IP (Entry Point)
14
SS2
12
SP2
10
SS1
8
SP1
6
SS0
4
SP0
2
Previous Task Link
0
Figure 7-10. 16-Bit TSS Format
7.7
TASK MANAGEMENT IN 64-BIT MODE
In 64-bit mode, task structure and task state are similar to those in protected mode. However, the task switching
mechanism available in protected mode is not supported in 64-bit mode. Task management and switching must be
performed by software. The processor issues a general-protection exception (#GP) if the following is attempted in
64-bit mode:
•
•
Control transfer to a TSS or a task gate using JMP, CALL, INTn, or interrupt.
An IRET with EFLAGS.NT (nested task) set to 1.
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TASK MANAGEMENT
Although hardware task-switching is not supported in 64-bit mode, a 64-bit task state segment (TSS) must exist.
Figure 7-11 shows the format of a 64-bit TSS. The TSS holds information important to 64-bit mode and that is not
directly related to the task-switch mechanism. This information includes:
•
•
•
RSPn — The full 64-bit canonical forms of the stack pointers (RSP) for privilege levels 0-2.
ISTn — The full 64-bit canonical forms of the interrupt stack table (IST) pointers.
I/O map base address — The 16-bit offset to the I/O permission bit map from the 64-bit TSS base.
The operating system must create at least one 64-bit TSS after activating IA-32e mode. It must execute the LTR
instruction (in 64-bit mode) to load the TR register with a pointer to the 64-bit TSS responsible for both 64-bitmode programs and compatibility-mode programs.
31
0
15
Reserved
I/O Map Base Address
Reserved
100
96
Reserved
92
IST7 (upper 32 bits)
88
IST7 (lower 32 bits)
84
IST6 (upper 32 bits)
80
IST6 (lower 32 bits)
76
IST5 (upper 32 bits)
72
IST5 (lower 32 bits)
68
IST4 (upper 32 bits)
64
IST4 (lower 32 bits)
60
IST3 (upper 32 bits)
56
IST3 (lower 32 bits)
52
IST2 (upper 32 bits)
48
IST2 (lower 32 bits)
44
IST1 (upper 32 bits)
40
IST1 (lower 32 bits)
36
Reserved
32
Reserved
28
RSP2 (upper 32 bits)
24
RSP2 (lower 32 bits)
20
RSP1 (upper 32 bits)
16
RSP1 (lower 32 bits)
12
RSP0 (upper 32 bits)
8
RSP0 (lower 32 bits)
4
Reserved
0
Reserved bits. Set to 0.
Figure 7-11. 64-Bit TSS Format
Vol. 3A 7-17
TASK MANAGEMENT
7-18 Vol. 3A
CHAPTER 8
MULTIPLE-PROCESSOR MANAGEMENT
The Intel 64 and IA-32 architectures provide mechanisms for managing and improving the performance of multiple
processors connected to the same system bus. These include:
•
•
Bus locking and/or cache coherency management for performing atomic operations on system memory.
•
An advance programmable interrupt controller (APIC) located on the processor chip (see Chapter 10,
“Advanced Programmable Interrupt Controller (APIC)”). This feature was introduced by the Pentium processor.
•
A second-level cache (level 2, L2). For the Pentium 4, Intel Xeon, and P6 family processors, the L2 cache is
included in the processor package and is tightly coupled to the processor. For the Pentium and Intel486
processors, pins are provided to support an external L2 cache.
•
A third-level cache (level 3, L3). For Intel Xeon processors, the L3 cache is included in the processor package
and is tightly coupled to the processor.
•
Intel Hyper-Threading Technology. This extension to the Intel 64 and IA-32 architectures enables a single
processor core to execute two or more threads concurrently (see Section 8.5, “Intel® Hyper-Threading
Technology and Intel® Multi-Core Technology”).
Serializing instructions. These instructions apply only to the Pentium 4, Intel Xeon, P6 family, and Pentium
processors.
These mechanisms are particularly useful in symmetric-multiprocessing (SMP) systems. However, they can also be
used when an Intel 64 or IA-32 processor and a special-purpose processor (such as a communications, graphics,
or video processor) share the system bus.
These multiprocessing mechanisms have the following characteristics:
•
To maintain system memory coherency — When two or more processors are attempting simultaneously to
access the same address in system memory, some communication mechanism or memory access protocol
must be available to promote data coherency and, in some instances, to allow one processor to temporarily lock
a memory location.
•
To maintain cache consistency — When one processor accesses data cached on another processor, it must not
receive incorrect data. If it modifies data, all other processors that access that data must receive the modified
data.
•
To allow predictable ordering of writes to memory — In some circumstances, it is important that memory writes
be observed externally in precisely the same order as programmed.
•
To distribute interrupt handling among a group of processors — When several processors are operating in a
system in parallel, it is useful to have a centralized mechanism for receiving interrupts and distributing them to
available processors for servicing.
•
To increase system performance by exploiting the multi-threaded and multi-process nature of contemporary
operating systems and applications.
The caching mechanism and cache consistency of Intel 64 and IA-32 processors are discussed in Chapter 11. The
APIC architecture is described in Chapter 10. Bus and memory locking, serializing instructions, memory ordering,
and Intel Hyper-Threading Technology are discussed in the following sections.
8.1
LOCKED ATOMIC OPERATIONS
The 32-bit IA-32 processors support locked atomic operations on locations in system memory. These operations
are typically used to manage shared data structures (such as semaphores, segment descriptors, system segments,
or page tables) in which two or more processors may try simultaneously to modify the same field or flag. The
processor uses three interdependent mechanisms for carrying out locked atomic operations:
•
•
Guaranteed atomic operations
Bus locking, using the LOCK# signal and the LOCK instruction prefix
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•
Cache coherency protocols that ensure that atomic operations can be carried out on cached data structures
(cache lock); this mechanism is present in the Pentium 4, Intel Xeon, and P6 family processors
These mechanisms are interdependent in the following ways. Certain basic memory transactions (such as reading
or writing a byte in system memory) are always guaranteed to be handled atomically. That is, once started, the
processor guarantees that the operation will be completed before another processor or bus agent is allowed access
to the memory location. The processor also supports bus locking for performing selected memory operations (such
as a read-modify-write operation in a shared area of memory) that typically need to be handled atomically, but are
not automatically handled this way. Because frequently used memory locations are often cached in a processor’s L1
or L2 caches, atomic operations can often be carried out inside a processor’s caches without asserting the bus lock.
Here the processor’s cache coherency protocols ensure that other processors that are caching the same memory
locations are managed properly while atomic operations are performed on cached memory locations.
NOTE
Where there are contested lock accesses, software may need to implement algorithms that ensure
fair access to resources in order to prevent lock starvation. The hardware provides no resource that
guarantees fairness to participating agents. It is the responsibility of software to manage the
fairness of semaphores and exclusive locking functions.
The mechanisms for handling locked atomic operations have evolved with the complexity of IA-32 processors. More
recent IA-32 processors (such as the Pentium 4, Intel Xeon, and P6 family processors) and Intel 64 provide a more
refined locking mechanism than earlier processors. These mechanisms are described in the following sections.
8.1.1
Guaranteed Atomic Operations
The Intel486 processor (and newer processors since) guarantees that the following basic memory operations will
always be carried out atomically:
•
•
•
Reading or writing a byte
Reading or writing a word aligned on a 16-bit boundary
Reading or writing a doubleword aligned on a 32-bit boundary
The Pentium processor (and newer processors since) guarantees that the following additional memory operations
will always be carried out atomically:
•
•
Reading or writing a quadword aligned on a 64-bit boundary
16-bit accesses to uncached memory locations that fit within a 32-bit data bus
The P6 family processors (and newer processors since) guarantee that the following additional memory operation
will always be carried out atomically:
•
Unaligned 16-, 32-, and 64-bit accesses to cached memory that fit within a cache line
Accesses to cacheable memory that are split across cache lines and page boundaries are not guaranteed to be
atomic by the Intel Core 2 Duo, Intel® Atom™, Intel Core Duo, Pentium M, Pentium 4, Intel Xeon, P6 family,
Pentium, and Intel486 processors. The Intel Core 2 Duo, Intel Atom, Intel Core Duo, Pentium M, Pentium 4, Intel
Xeon, and P6 family processors provide bus control signals that permit external memory subsystems to make split
accesses atomic; however, nonaligned data accesses will seriously impact the performance of the processor and
should be avoided.
An x87 instruction or an SSE instructions that accesses data larger than a quadword may be implemented using
multiple memory accesses. If such an instruction stores to memory, some of the accesses may complete (writing
to memory) while another causes the operation to fault for architectural reasons (e.g. due an page-table entry that
is marked “not present”). In this case, the effects of the completed accesses may be visible to software even
though the overall instruction caused a fault. If TLB invalidation has been delayed (see Section 4.10.4.4), such
page faults may occur even if all accesses are to the same page.
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8.1.2
Bus Locking
Intel 64 and IA-32 processors provide a LOCK# signal that is asserted automatically during certain critical memory
operations to lock the system bus or equivalent link. While this output signal is asserted, requests from other
processors or bus agents for control of the bus are blocked. Software can specify other occasions when the LOCK
semantics are to be followed by prepending the LOCK prefix to an instruction.
In the case of the Intel386, Intel486, and Pentium processors, explicitly locked instructions will result in the assertion of the LOCK# signal. It is the responsibility of the hardware designer to make the LOCK# signal available in
system hardware to control memory accesses among processors.
For the P6 and more recent processor families, if the memory area being accessed is cached internally in the
processor, the LOCK# signal is generally not asserted; instead, locking is only applied to the processor’s caches
(see Section 8.1.4, “Effects of a LOCK Operation on Internal Processor Caches”).
8.1.2.1
Automatic Locking
The operations on which the processor automatically follows the LOCK semantics are as follows:
•
•
•
When executing an XCHG instruction that references memory.
When setting the B (busy) flag of a TSS descriptor — The processor tests and sets the busy flag in the
type field of the TSS descriptor when switching to a task. To ensure that two processors do not switch to the
same task simultaneously, the processor follows the LOCK semantics while testing and setting this flag.
When updating segment descriptors — When loading a segment descriptor, the processor will set the
accessed flag in the segment descriptor if the flag is clear. During this operation, the processor follows the
LOCK semantics so that the descriptor will not be modified by another processor while it is being updated. For
this action to be effective, operating-system procedures that update descriptors should use the following steps:
— Use a locked operation to modify the access-rights byte to indicate that the segment descriptor is notpresent, and specify a value for the type field that indicates that the descriptor is being updated.
— Update the fields of the segment descriptor. (This operation may require several memory accesses;
therefore, locked operations cannot be used.)
— Use a locked operation to modify the access-rights byte to indicate that the segment descriptor is valid and
present.
•
The Intel386 processor always updates the accessed flag in the segment descriptor, whether it is clear or not.
The Pentium 4, Intel Xeon, P6 family, Pentium, and Intel486 processors only update this flag if it is not already
set.
•
When updating page-directory and page-table entries — When updating page-directory and page-table
entries, the processor uses locked cycles to set the accessed and dirty flag in the page-directory and page-table
entries.
•
Acknowledging interrupts — After an interrupt request, an interrupt controller may use the data bus to send
the interrupt vector for the interrupt to the processor. The processor follows the LOCK semantics during this
time to ensure that no other data appears on the data bus when the interrupt vector is being transmitted.
8.1.2.2
Software Controlled Bus Locking
To explicitly force the LOCK semantics, software can use the LOCK prefix with the following instructions when they
are used to modify a memory location. An invalid-opcode exception (#UD) is generated when the LOCK prefix is
used with any other instruction or when no write operation is made to memory (that is, when the destination
operand is in a register).
•
•
•
•
•
The bit test and modify instructions (BTS, BTR, and BTC).
The exchange instructions (XADD, CMPXCHG, and CMPXCHG8B).
The LOCK prefix is automatically assumed for XCHG instruction.
The following single-operand arithmetic and logical instructions: INC, DEC, NOT, and NEG.
The following two-operand arithmetic and logical instructions: ADD, ADC, SUB, SBB, AND, OR, and XOR.
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A locked instruction is guaranteed to lock only the area of memory defined by the destination operand, but may be
interpreted by the system as a lock for a larger memory area.
Software should access semaphores (shared memory used for signalling between multiple processors) using identical addresses and operand lengths. For example, if one processor accesses a semaphore using a word access,
other processors should not access the semaphore using a byte access.
NOTE
Do not implement semaphores using the WC memory type. Do not perform non-temporal stores to
a cache line containing a location used to implement a semaphore.
The integrity of a bus lock is not affected by the alignment of the memory field. The LOCK semantics are followed
for as many bus cycles as necessary to update the entire operand. However, it is recommend that locked accesses
be aligned on their natural boundaries for better system performance:
•
•
•
•
Any boundary for an 8-bit access (locked or otherwise).
16-bit boundary for locked word accesses.
32-bit boundary for locked doubleword accesses.
64-bit boundary for locked quadword accesses.
Locked operations are atomic with respect to all other memory operations and all externally visible events. Only
instruction fetch and page table accesses can pass locked instructions. Locked instructions can be used to synchronize data written by one processor and read by another processor.
For the P6 family processors, locked operations serialize all outstanding load and store operations (that is, wait for
them to complete). This rule is also true for the Pentium 4 and Intel Xeon processors, with one exception. Load
operations that reference weakly ordered memory types (such as the WC memory type) may not be serialized.
Locked instructions should not be used to ensure that data written can be fetched as instructions.
NOTE
The locked instructions for the current versions of the Pentium 4, Intel Xeon, P6 family, Pentium,
and Intel486 processors allow data written to be fetched as instructions. However, Intel
recommends that developers who require the use of self-modifying code use a different synchronizing mechanism, described in the following sections.
8.1.3
Handling Self- and Cross-Modifying Code
The act of a processor writing data into a currently executing code segment with the intent of executing that data
as code is called self-modifying code. IA-32 processors exhibit model-specific behavior when executing selfmodified code, depending upon how far ahead of the current execution pointer the code has been modified.
As processor microarchitectures become more complex and start to speculatively execute code ahead of the retirement point (as in P6 and more recent processor families), the rules regarding which code should execute, pre- or
post-modification, become blurred. To write self-modifying code and ensure that it is compliant with current and
future versions of the IA-32 architectures, use one of the following coding options:
(* OPTION 1 *)
Store modified code (as data) into code segment;
Jump to new code or an intermediate location;
Execute new code;
(* OPTION 2 *)
Store modified code (as data) into code segment;
Execute a serializing instruction; (* For example, CPUID instruction *)
Execute new code;
The use of one of these options is not required for programs intended to run on the Pentium or Intel486 processors,
but are recommended to ensure compatibility with the P6 and more recent processor families.
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Self-modifying code will execute at a lower level of performance than non-self-modifying or normal code. The
degree of the performance deterioration will depend upon the frequency of modification and specific characteristics
of the code.
The act of one processor writing data into the currently executing code segment of a second processor with the
intent of having the second processor execute that data as code is called cross-modifying code. As with selfmodifying code, IA-32 processors exhibit model-specific behavior when executing cross-modifying code,
depending upon how far ahead of the executing processors current execution pointer the code has been modified.
To write cross-modifying code and ensure that it is compliant with current and future versions of the IA-32 architecture, the following processor synchronization algorithm must be implemented:
(* Action of Modifying Processor *)
Memory_Flag ← 0; (* Set Memory_Flag to value other than 1 *)
Store modified code (as data) into code segment;
Memory_Flag ← 1;
(* Action of Executing Processor *)
WHILE (Memory_Flag ≠ 1)
Wait for code to update;
ELIHW;
Execute serializing instruction; (* For example, CPUID instruction *)
Begin executing modified code;
(The use of this option is not required for programs intended to run on the Intel486 processor, but is recommended
to ensure compatibility with the Pentium 4, Intel Xeon, P6 family, and Pentium processors.)
Like self-modifying code, cross-modifying code will execute at a lower level of performance than non-cross-modifying (normal) code, depending upon the frequency of modification and specific characteristics of the code.
The restrictions on self-modifying code and cross-modifying code also apply to the Intel 64 architecture.
8.1.4
Effects of a LOCK Operation on Internal Processor Caches
For the Intel486 and Pentium processors, the LOCK# signal is always asserted on the bus during a LOCK operation,
even if the area of memory being locked is cached in the processor.
For the P6 and more recent processor families, if the area of memory being locked during a LOCK operation is
cached in the processor that is performing the LOCK operation as write-back memory and is completely contained
in a cache line, the processor may not assert the LOCK# signal on the bus. Instead, it will modify the memory location internally and allow it’s cache coherency mechanism to ensure that the operation is carried out atomically. This
operation is called “cache locking.” The cache coherency mechanism automatically prevents two or more processors that have cached the same area of memory from simultaneously modifying data in that area.
8.2
MEMORY ORDERING
The term memory ordering refers to the order in which the processor issues reads (loads) and writes (stores)
through the system bus to system memory. The Intel 64 and IA-32 architectures support several memory-ordering
models depending on the implementation of the architecture. For example, the Intel386 processor enforces
program ordering (generally referred to as strong ordering), where reads and writes are issued on the system
bus in the order they occur in the instruction stream under all circumstances.
To allow performance optimization of instruction execution, the IA-32 architecture allows departures from strongordering model called processor ordering in Pentium 4, Intel Xeon, and P6 family processors. These processorordering variations (called here the memory-ordering model) allow performance enhancing operations such as
allowing reads to go ahead of buffered writes. The goal of any of these variations is to increase instruction execution speeds, while maintaining memory coherency, even in multiple-processor systems.
Section 8.2.1 and Section 8.2.2 describe the memory-ordering implemented by Intel486, Pentium, Intel Core 2
Duo, Intel Atom, Intel Core Duo, Pentium 4, Intel Xeon, and P6 family processors. Section 8.2.3 gives examples
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illustrating the behavior of the memory-ordering model on IA-32 and Intel-64 processors. Section 8.2.4 considers
the special treatment of stores for string operations and Section 8.2.5 discusses how memory-ordering behavior
may be modified through the use of specific instructions.
8.2.1
Memory Ordering in the Intel® Pentium® and Intel486™ Processors
The Pentium and Intel486 processors follow the processor-ordered memory model; however, they operate as
strongly-ordered processors under most circumstances. Reads and writes always appear in programmed order at
the system bus—except for the following situation where processor ordering is exhibited. Read misses are
permitted to go ahead of buffered writes on the system bus when all the buffered writes are cache hits and, therefore, are not directed to the same address being accessed by the read miss.
In the case of I/O operations, both reads and writes always appear in programmed order.
Software intended to operate correctly in processor-ordered processors (such as the Pentium 4, Intel Xeon, and P6
family processors) should not depend on the relatively strong ordering of the Pentium or Intel486 processors.
Instead, it should ensure that accesses to shared variables that are intended to control concurrent execution
among processors are explicitly required to obey program ordering through the use of appropriate locking or serializing operations (see Section 8.2.5, “Strengthening or Weakening the Memory-Ordering Model”).
8.2.2
Memory Ordering in P6 and More Recent Processor Families
The Intel Core 2 Duo, Intel Atom, Intel Core Duo, Pentium 4, and P6 family processors also use a processor-ordered
memory-ordering model that can be further defined as “write ordered with store-buffer forwarding.” This model
can be characterized as follows.
In a single-processor system for memory regions defined as write-back cacheable, the memory-ordering model
respects the following principles (Note the memory-ordering principles for single-processor and multipleprocessor systems are written from the perspective of software executing on the processor, where the term
“processor” refers to a logical processor. For example, a physical processor supporting multiple cores and/or
HyperThreading Technology is treated as a multi-processor systems.):
•
•
•
Reads are not reordered with other reads.
Writes are not reordered with older reads.
Writes to memory are not reordered with other writes, with the following exceptions:
— writes executed with the CLFLUSH instruction;
— streaming stores (writes) executed with the non-temporal move instructions (MOVNTI, MOVNTQ,
MOVNTDQ, MOVNTPS, and MOVNTPD); and
— string operations (see Section 8.2.4.1).
•
•
•
•
•
•
•
Reads may be reordered with older writes to different locations but not with older writes to the same location.
Reads or writes cannot be reordered with I/O instructions, locked instructions, or serializing instructions.
Reads cannot pass earlier LFENCE and MFENCE instructions.
Writes cannot pass earlier LFENCE, SFENCE, and MFENCE instructions.
LFENCE instructions cannot pass earlier reads.
SFENCE instructions cannot pass earlier writes.
MFENCE instructions cannot pass earlier reads or writes.
In a multiple-processor system, the following ordering principles apply:
•
•
•
•
•
Individual processors use the same ordering principles as in a single-processor system.
Writes by a single processor are observed in the same order by all processors.
Writes from an individual processor are NOT ordered with respect to the writes from other processors.
Memory ordering obeys causality (memory ordering respects transitive visibility).
Any two stores are seen in a consistent order by processors other than those performing the stores
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•
Locked instructions have a total order.
See the example in Figure 8-1. Consider three processors in a system and each processor performs three writes,
one to each of three defined locations (A, B, and C). Individually, the processors perform the writes in the same
program order, but because of bus arbitration and other memory access mechanisms, the order that the three
processors write the individual memory locations can differ each time the respective code sequences are executed
on the processors. The final values in location A, B, and C would possibly vary on each execution of the write
sequence.
The processor-ordering model described in this section is virtually identical to that used by the Pentium and
Intel486 processors. The only enhancements in the Pentium 4, Intel Xeon, and P6 family processors are:
•
•
•
Added support for speculative reads, while still adhering to the ordering principles above.
Store-buffer forwarding, when a read passes a write to the same memory location.
Out of order store from long string store and string move operations (see Section 8.2.4, “Fast-String Operation
and Out-of-Order Stores,” below).
Order of Writes From Individual Processors
Processor #1
Each processor
is guaranteed to
perform writes in
program order.
Write A.1
Write B.1
Write C.1
Processor #2
Write A.2
Write B.2
Write C.2
Processor #3
Write A.3
Write B.3
Write C.3
Example of order of actual writes
from all processors to memory
Writes are in order
with respect to
individual processes.
Write A.1
Write B.1
Write A.2
Write A.3
Write C.1
Write B.2
Write C.2
Write B.3
Write C.3
Writes from all
processors are
not guaranteed
to occur in a
particular order.
Figure 8-1. Example of Write Ordering in Multiple-Processor Systems
NOTE
In P6 processor family, store-buffer forwarding to reads of WC memory from streaming stores to the same address
does not occur due to errata.
8.2.3
Examples Illustrating the Memory-Ordering Principles
This section provides a set of examples that illustrate the behavior of the memory-ordering principles introduced in
Section 8.2.2. They are designed to give software writers an understanding of how memory ordering may affect
the results of different sequences of instructions.
These examples are limited to accesses to memory regions defined as write-back cacheable (WB). (Section 8.2.3.1
describes other limitations on the generality of the examples.) The reader should understand that they describe
only software-visible behavior. A logical processor may reorder two accesses even if one of examples indicates that
they may not be reordered. Such an example states only that software cannot detect that such a reordering
occurred. Similarly, a logical processor may execute a memory access more than once as long as the behavior
visible to software is consistent with a single execution of the memory access.
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8.2.3.1
Assumptions, Terminology, and Notation
As noted above, the examples in this section are limited to accesses to memory regions defined as write-back
cacheable (WB). They apply only to ordinary loads stores and to locked read-modify-write instructions. They do not
necessarily apply to any of the following: out-of-order stores for string instructions (see Section 8.2.4); accesses
with a non-temporal hint; reads from memory by the processor as part of address translation (e.g., page walks);
and updates to segmentation and paging structures by the processor (e.g., to update “accessed” bits).
The principles underlying the examples in this section apply to individual memory accesses and to locked readmodify-write instructions. The Intel-64 memory-ordering model guarantees that, for each of the following
memory-access instructions, the constituent memory operation appears to execute as a single memory access:
•
•
•
•
Instructions that read or write a single byte.
Instructions that read or write a word (2 bytes) whose address is aligned on a 2 byte boundary.
Instructions that read or write a doubleword (4 bytes) whose address is aligned on a 4 byte boundary.
Instructions that read or write a quadword (8 bytes) whose address is aligned on an 8 byte boundary.
Any locked instruction (either the XCHG instruction or another read-modify-write instruction with a LOCK prefix)
appears to execute as an indivisible and uninterruptible sequence of load(s) followed by store(s) regardless of
alignment.
Other instructions may be implemented with multiple memory accesses. From a memory-ordering point of view,
there are no guarantees regarding the relative order in which the constituent memory accesses are made. There is
also no guarantee that the constituent operations of a store are executed in the same order as the constituent
operations of a load.
Section 8.2.3.2 through Section 8.2.3.7 give examples using the MOV instruction. The principles that underlie
these examples apply to load and store accesses in general and to other instructions that load from or store to
memory. Section 8.2.3.8 and Section 8.2.3.9 give examples using the XCHG instruction. The principles that
underlie these examples apply to other locked read-modify-write instructions.
This section uses the term “processor” is to refer to a logical processor. The examples are written using Intel-64
assembly-language syntax and use the following notational conventions:
•
Arguments beginning with an “r”, such as r1 or r2 refer to registers (e.g., EAX) visible only to the processor
being considered.
•
•
•
Memory locations are denoted with x, y, z.
Stores are written as mov [ _x], val, which implies that val is being stored into the memory location x.
Loads are written as mov r, [ _x], which implies that the contents of the memory location x are being loaded
into the register r.
As noted earlier, the examples refer only to software visible behavior. When the succeeding sections make statement such as “the two stores are reordered,” the implication is only that “the two stores appear to be reordered
from the point of view of software.”
8.2.3.2
Neither Loads Nor Stores Are Reordered with Like Operations
The Intel-64 memory-ordering model allows neither loads nor stores to be reordered with the same kind of operation. That is, it ensures that loads are seen in program order and that stores are seen in program order. This is illustrated by the following example:
Example 8-1. Stores Are Not Reordered with Other Stores
Processor 0
Processor 1
mov [ _x], 1
mov r1, [ _y]
mov [ _y], 1
mov r2, [ _x]
Initially x = y = 0
r1 = 1 and r2 = 0 is not allowed
The disallowed return values could be exhibited only if processor 0’s two stores are reordered (with the two loads
occurring between them) or if processor 1’s two loads are reordered (with the two stores occurring between them).
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If r1 = 1, the store to y occurs before the load from y. Because the Intel-64 memory-ordering model does not allow
stores to be reordered, the earlier store to x occurs before the load from y. Because the Intel-64 memory-ordering
model does not allow loads to be reordered, the store to x also occurs before the later load from x. This r2 = 1.
8.2.3.3
Stores Are Not Reordered With Earlier Loads
The Intel-64 memory-ordering model ensures that a store by a processor may not occur before a previous load by
the same processor. This is illustrated by the following example:
Example 8-2. Stores Are Not Reordered with Older Loads
Processor 0
Processor 1
mov r1, [ _x]
mov r2, [ _y]
mov [ _y], 1
mov [ _x], 1
Initially x = y = 0
r1 = 1 and r2 = 1 is not allowed
Assume r1 = 1.
•
•
Because r1 = 1, processor 1’s store to x occurs before processor 0’s load from x.
•
•
Similarly, processor 0’s load from x occurs before its store to y.
Because the Intel-64 memory-ordering model prevents each store from being reordered with the earlier load
by the same processor, processor 1’s load from y occurs before its store to x.
Thus, processor 1’s load from y occurs before processor 0’s store to y, implying r2 = 0.
8.2.3.4
Loads May Be Reordered with Earlier Stores to Different Locations
The Intel-64 memory-ordering model allows a load to be reordered with an earlier store to a different location.
However, loads are not reordered with stores to the same location.
The fact that a load may be reordered with an earlier store to a different location is illustrated by the following
example:
Example 8-3. Loads May be Reordered with Older Stores
Processor 0
Processor 1
mov [ _x], 1
mov [ _y], 1
mov r1, [ _y]
mov r2, [ _x]
Initially x = y = 0
r1 = 0 and r2 = 0 is allowed
At each processor, the load and the store are to different locations and hence may be reordered. Any interleaving
of the operations is thus allowed. One such interleaving has the two loads occurring before the two stores. This
would result in each load returning value 0.
The fact that a load may not be reordered with an earlier store to the same location is illustrated by the following
example:
Example 8-4. Loads Are not Reordered with Older Stores to the Same Location
Processor 0
mov [ _x], 1
mov r1, [ _x]
Initially x = 0
r1 = 0 is not allowed
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The Intel-64 memory-ordering model does not allow the load to be reordered with the earlier store because the
accesses are to the same location. Therefore, r1 = 1 must hold.
8.2.3.5
Intra-Processor Forwarding Is Allowed
The memory-ordering model allows concurrent stores by two processors to be seen in different orders by those two
processors; specifically, each processor may perceive its own store occurring before that of the other. This is illustrated by the following example:
Example 8-5. Intra-Processor Forwarding is Allowed
Processor 0
Processor 1
mov [ _x], 1
mov [ _y], 1
mov r1, [ _x]
mov r3, [ _y]
mov r2, [ _y]
mov r4, [ _x]
Initially x = y = 0
r2 = 0 and r4 = 0 is allowed
The memory-ordering model imposes no constraints on the order in which the two stores appear to execute by the
two processors. This fact allows processor 0 to see its store before seeing processor 1's, while processor 1 sees its
store before seeing processor 0's. (Each processor is self consistent.) This allows r2 = 0 and r4 = 0.
In practice, the reordering in this example can arise as a result of store-buffer forwarding. While a store is temporarily held in a processor's store buffer, it can satisfy the processor's own loads but is not visible to (and cannot
satisfy) loads by other processors.
8.2.3.6
Stores Are Transitively Visible
The memory-ordering model ensures transitive visibility of stores; stores that are causally related appear to all
processors to occur in an order consistent with the causality relation. This is illustrated by the following example:
Example 8-6. Stores Are Transitively Visible
Processor 0
mov [ _x], 1
Processor 1
Processor 2
mov r1, [ _x]
mov [ _y], 1
mov r2, [ _y]
mov r3, [_x]
Initially x = y = 0
r1 = 1, r2 = 1, r3 = 0 is not allowed
Assume that r1 = 1 and r2 = 1.
•
•
Because r1 = 1, processor 0’s store occurs before processor 1’s load.
•
Because processor 0’s store causally precedes processor 1’s store, the memory-ordering model ensures that
processor 0’s store appears to occur before processor 1’s store from the point of view of all processors.
•
•
Because r2 = 1, processor 1’s store occurs before processor 2’s load.
•
The above items imply that processor 0’s store to x occurs before processor 2’s load from x. This implies that
r3 = 1.
Because the memory-ordering model prevents a store from being reordered with an earlier load (see Section
8.2.3.3), processor 1’s load occurs before its store. Thus, processor 0’s store causally precedes processor 1’s
store.
Because the Intel-64 memory-ordering model prevents loads from being reordered (see Section 8.2.3.2),
processor 2’s load occur in order.
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8.2.3.7
Stores Are Seen in a Consistent Order by Other Processors
As noted in Section 8.2.3.5, the memory-ordering model allows stores by two processors to be seen in different
orders by those two processors. However, any two stores must appear to execute in the same order to all processors other than those performing the stores. This is illustrated by the following example:
Example 8-7. Stores Are Seen in a Consistent Order by Other Processors
Processor 0
Processor 1
Processor 2
mov [ _x], 1
mov [ _y], 1
Processor 3
mov r1, [ _x]
mov r3, [_y]
mov r2, [ _y]
mov r4, [_x]
Initially x = y =0
r1 = 1, r2 = 0, r3 = 1, r4 = 0 is not allowed
By the principles discussed in Section 8.2.3.2,
•
•
•
•
processor 2’s first and second load cannot be reordered,
processor 3’s first and second load cannot be reordered.
If r1 = 1 and r2 = 0, processor 0’s store appears to precede processor 1’s store with respect to processor 2.
Similarly, r3 = 1 and r4 = 0 imply that processor 1’s store appears to precede processor 0’s store with respect
to processor 1.
Because the memory-ordering model ensures that any two stores appear to execute in the same order to all
processors (other than those performing the stores), this set of return values is not allowed
8.2.3.8
Locked Instructions Have a Total Order
The memory-ordering model ensures that all processors agree on a single execution order of all locked instructions, including those that are larger than 8 bytes or are not naturally aligned. This is illustrated by the following
example:
Example 8-8. Locked Instructions Have a Total Order
Processor 0
Processor 1
xchg [ _x], r1
Processor 2
Processor 3
xchg [ _y], r2
mov r3, [ _x]
mov r5, [_y]
mov r4, [ _y]
mov r6, [_x]
Initially r1 = r2 = 1, x = y = 0
r3 = 1, r4 = 0, r5 = 1, r6 = 0 is not allowed
Processor 2 and processor 3 must agree on the order of the two executions of XCHG. Without loss of generality,
suppose that processor 0’s XCHG occurs first.
•
•
If r5 = 1, processor 1’s XCHG into y occurs before processor 3’s load from y.
•
Since processor 0’s XCHG into x occurs before processor 1’s XCHG (by assumption), it occurs before
processor 3’s load from x. Thus, r6 = 1.
Because the Intel-64 memory-ordering model prevents loads from being reordered (see Section 8.2.3.2),
processor 3’s loads occur in order and, therefore, processor 1’s XCHG occurs before processor 3’s load from x.
A similar argument (referring instead to processor 2’s loads) applies if processor 1’s XCHG occurs before
processor 0’s XCHG.
8.2.3.9
Loads and Stores Are Not Reordered with Locked Instructions
The memory-ordering model prevents loads and stores from being reordered with locked instructions that execute
earlier or later. The examples in this section illustrate only cases in which a locked instruction is executed before a
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load or a store. The reader should note that reordering is prevented also if the locked instruction is executed after
a load or a store.
The first example illustrates that loads may not be reordered with earlier locked instructions:
Example 8-9. Loads Are not Reordered with Locks
Processor 0
Processor 1
xchg [ _x], r1
xchg [ _y], r3
mov r2, [ _y]
mov r4, [ _x]
Initially x = y = 0, r1 = r3 = 1
r2 = 0 and r4 = 0 is not allowed
As explained in Section 8.2.3.8, there is a total order of the executions of locked instructions. Without loss of
generality, suppose that processor 0’s XCHG occurs first.
Because the Intel-64 memory-ordering model prevents processor 1’s load from being reordered with its earlier
XCHG, processor 0’s XCHG occurs before processor 1’s load. This implies r4 = 1.
A similar argument (referring instead to processor 2’s accesses) applies if processor 1’s XCHG occurs before
processor 0’s XCHG.
The second example illustrates that a store may not be reordered with an earlier locked instruction:
Example 8-10. Stores Are not Reordered with Locks
Processor 0
Processor 1
xchg [ _x], r1
mov r2, [ _y]
mov [ _y], 1
mov r3, [ _x]
Initially x = y = 0, r1 = 1
r2 = 1 and r3 = 0 is not allowed
Assume r2 = 1.
•
•
Because r2 = 1, processor 0’s store to y occurs before processor 1’s load from y.
•
Because the memory-ordering model prevents loads from being reordered (see Section 8.2.3.2), processor 1’s
loads occur in order and, therefore, processor 1’s XCHG into x occurs before processor 1’s load from x. Thus,
r3 = 1.
Because the memory-ordering model prevents a store from being reordered with an earlier locked instruction,
processor 0’s XCHG into x occurs before its store to y. Thus, processor 0’s XCHG into x occurs before
processor 1’s load from y.
8.2.4
Fast-String Operation and Out-of-Order Stores
Section 7.3.9.3 of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 described an optimization of repeated string operations called fast-string operation.
As explained in that section, the stores produced by fast-string operation may appear to execute out of order. Software dependent upon sequential store ordering should not use string operations for the entire data structure to be
stored. Data and semaphores should be separated. Order-dependent code should write to a discrete semaphore
variable after any string operations to allow correctly ordered data to be seen by all processors. Atomicity of load
and store operations is guaranteed only for native data elements of the string with native data size, and only if they
are included in a single cache line.
Section 8.2.4.1 and Section 8.2.4.2 provide further explain and examples.
8.2.4.1
Memory-Ordering Model for String Operations on Write-Back (WB) Memory
This section deals with the memory-ordering model for string operations on write-back (WB) memory for the Intel
64 architecture.
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The memory-ordering model respects the follow principles:
1. Stores within a single string operation may be executed out of order.
2. Stores from separate string operations (for example, stores from consecutive string operations) do not execute
out of order. All the stores from an earlier string operation will complete before any store from a later string
operation.
3. String operations are not reordered with other store operations.
Fast string operations (e.g. string operations initiated with the MOVS/STOS instructions and the REP prefix) may be
interrupted by exceptions or interrupts. The interrupts are precise but may be delayed - for example, the interruptions may be taken at cache line boundaries, after every few iterations of the loop, or after operating on every few
bytes. Different implementations may choose different options, or may even choose not to delay interrupt
handling, so software should not rely on the delay. When the interrupt/trap handler is reached, the source/destination registers point to the next string element to be operated on, while the EIP stored in the stack points to the
string instruction, and the ECX register has the value it held following the last successful iteration. The return from
that trap/interrupt handler should cause the string instruction to be resumed from the point where it was interrupted.
The string operation memory-ordering principles, (item 2 and 3 above) should be interpreted by taking the incorruptibility of fast string operations into account. For example, if a fast string operation gets interrupted after k iterations, then stores performed by the interrupt handler will become visible after the fast string stores from iteration
0 to k, and before the fast string stores from the (k+1)th iteration onward.
Stores within a single string operation may execute out of order (item 1 above) only if fast string operation is
enabled. Fast string operations are enabled/disabled through the IA32_MISC_ENABLE model specific register.
8.2.4.2
Examples Illustrating Memory-Ordering Principles for String Operations
The following examples uses the same notation and convention as described in Section 8.2.3.1.
In Example 8-11, processor 0 does one round of (128 iterations) doubleword string store operation via rep:stosd,
writing the value 1 (value in EAX) into a block of 512 bytes from location _x (kept in ES:EDI) in ascending order.
Since each operation stores a doubleword (4 bytes), the operation is repeated 128 times (value in ECX). The block
of memory initially contained 0. Processor 1 is reading two memory locations that are part of the memory block
being updated by processor 0, i.e, reading locations in the range _x to (_x+511).
Example 8-11. Stores Within a String Operation May be Reordered
Processor 0
rep:stosd [ _x]
Processor 1
mov r1, [ _z]
mov r2, [ _y]
Initially on processor 0: EAX = 1, ECX=128, ES:EDI =_x
Initially [_x] to 511[_x]= 0, _x <= _y < _z < _x+512
r1 = 1 and r2 = 0 is allowed
It is possible for processor 1 to perceive that the repeated string stores in processor 0 are happening out of order.
Assume that fast string operations are enabled on processor 0.
In Example 8-12, processor 0 does two separate rounds of rep stosd operation of 128 doubleword stores, writing
the value 1 (value in EAX) into the first block of 512 bytes from location _x (kept in ES:EDI) in ascending order. It
then writes 1 into a second block of memory from (_x+512) to (_x+1023). All of the memory locations initially
contain 0. The block of memory initially contained 0. Processor 1 performs two load operations from the two blocks
of memory.
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Example 8-12. Stores Across String Operations Are not Reordered
Processor 0
Processor 1
rep:stosd [ _x]
mov r1, [ _z]
mov ecx, $128
mov r2, [ _y]
rep:stosd 512[ _x]
Initially on processor 0: EAX = 1, ECX=128, ES:EDI =_x
Initially [_x] to 1023[_x]= 0, _x <= _y < _x+512 < _z < _x+1024
r1 = 1 and r2 = 0 is not allowed
It is not possible in the above example for processor 1 to perceive any of the stores from the later string operation
(to the second 512 block) in processor 0 before seeing the stores from the earlier string operation to the first 512
block.
The above example assumes that writes to the second block (_x+512 to _x+1023) does not get executed while
processor 0’s string operation to the first block has been interrupted. If the string operation to the first block by
processor 0 is interrupted, and a write to the second memory block is executed by the interrupt handler, then that
change in the second memory block will be visible before the string operation to the first memory block resumes.
In Example 8-13, processor 0 does one round of (128 iterations) doubleword string store operation via rep:stosd,
writing the value 1 (value in EAX) into a block of 512 bytes from location _x (kept in ES:EDI) in ascending order. It
then writes to a second memory location outside the memory block of the previous string operation. Processor 1
performs two read operations, the first read is from an address outside the 512-byte block but to be updated by
processor 0, the second ready is from inside the block of memory of string operation.
Example 8-13. String Operations Are not Reordered with later Stores
Processor 0
rep:stosd [ _x]
mov r1, [ _z]
mov [_z], $1
mov r2, [ _y]
Processor 1
Initially on processor 0: EAX = 1, ECX=128, ES:EDI =_x
Initially [_y] = [_z] = 0, [_x] to 511[_x]= 0, _x <= _y < _x+512, _z is a separate memory location
r1 = 1 and r2 = 0 is not allowed
Processor 1 cannot perceive the lat