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Vol. 3A 6-11
TASK MANAGEMENT
6.2.5 Task-Gate Descriptor
A task-gate descriptor provides an indirect, protected reference to a task (see Figure 6-6). 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.
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 6-6. Task-Gate Descriptor
31
16
15
13
14 12
11
87
0
P
D
P
L
Type
0
31
16
15
0
TSS Segment Selector
1010
DPL
P
TYPE
Descriptor Privilege Level
Segment Present
Segment Type
4
0
Reserved
Reserved
Reserved
- IA-32 Intel 1
- Architecture 1
- Software Developer’s Manual 1
- CONTENTS FOR VOLUME 3A AND 3B 3
- Vol. 3A v 5
- Vol. 3A vii 7
- Vol. 3A ix 9
- Vol. 3A xi 11
- Vol. 3A xiii 13
- Vol. 3A xv 15
- Vol. 3A xvii 17
- Vol. 3A xix 19
- Vol. 3A xxi 21
- Vol. 3A xxiii 23
- Vol. 3A xxv 25
- Vol. 3A xxvii 27
- Vol. 3A xxix 29
- Vol. 3A xxxi 31
- Vol. 3A xxxiii 33
- About This Manual 35
- CHAPTER 1 37
- ABOUT THIS MANUAL 37
- 1.3 NOTATIONAL CONVENTIONS 40
- 1.3.1 Bit and Byte Order 41
- 1.3.3 Instruction Operands 42
- 1.3.5 Segmented Addressing 43
- 1.3.7 Exceptions 44
- 1.4 RELATED LITERATURE 45
- System Architecture 47
- Overview 47
- CHAPTER 2 49
- SYSTEM ARCHITECTURE OVERVIEW 49
- Linear Address 51
- Tab leDirectory 52
- 2.1.5 Memory Management 55
- 2.1.6 System Registers 56
- 2.1.7 Other System Resources 58
- 2.2 MODES OF OPERATION 58
- 2.4.4 Task Register (TR) 64
- 2.5 CONTROL REGISTERS 64
- Counters 76
- Protected-Mode 79
- CHAPTER 3 81
- Logical Address 82
- 3.2 USING SEGMENTS 83
- 3.2.1 Basic Flat Model 83
- 3.2.2 Protected Flat Model 83
- Figure 3-2. Flat Model 84
- 3.2.3 Multi-Segment Model 85
- 3.2.5 Paging and Segmentation 86
- 3.3 PHYSICAL ADDRESS SPACE 86
- Vol. 3A 3-7 87
- 3.4.2 Segment Selectors 88
- 3.4.3 Segment Registers 89
- Vol. 3A 3-11 91
- 3.4.5 Segment Descriptors 92
- Vol. 3A 3-13 93
- 3-14 Vol. 3A 94
- 3-16 Vol. 3A 96
- 3.5 SYSTEM DESCRIPTOR TYPES 97
- 3-20 Vol. 3A 100
- 3.6.1 Paging Options 101
- ADDRESSING 102
- Page Directory 103
- 3.7.4 Memory Aliasing 105
- 3-28 Vol. 3A 108
- Vol. 3A 3-29 109
- MECHANISM 110
- Vol. 3A 3-31 111
- Addressing Enabled 114
- Vol. 3A 3-35 115
- PAGING MECHANISM 117
- Vol. 3A 3-39 119
- Physical Addr 120
- 3-42 Vol. 3A 122
- Vol. 3A 3-43 123
- MOV CR3, EAX 126
- Vol. 3A 3-47 127
- 3-48 Vol. 3A 128
- Protection 129
- CHAPTER 4 131
- PROTECTION 131
- PAGE-LEVEL PROTECTION 132
- 4.3 LIMIT CHECKING 135
- • The type field 136
- 4.5 PRIVILEGE LEVELS 138
- Figure 4-3. Protection Rings 139
- SEGMENTS 141
- REGISTER 143
- From Various Privilege Levels 146
- • Call gates 147
- • Trap gates 147
- • Interrupt gates 147
- • Task gates 147
- 4.8.3 Call Gates 148
- Segment Selector 151
- 4.8.5 Stack Switching 153
- 4.9 PRIVILEGED INSTRUCTIONS 162
- 4.10 POINTER VALIDATION 162
- Instructions) 164
- Instruction) 164
- 4.10.5 Checking Alignment 167
- 4.11 PAGE-LEVEL PROTECTION 167
- 4.11.1 Page-Protection Flags 168
- 4.11.3 Page Type 168
- • IA-32e mode 170
- 4.13.3 Reserved Bit Checking 173
- • IA32_EFER.NXE = 1 174
- Interrupt and 175
- Exception Handling 175
- CHAPTER 5 177
- 5.3 SOURCES OF INTERRUPTS 178
- 5.3.1 External Interrupts 178
- 5-4 Vol. 3A 180
- • Machine-check exceptions 181
- 5.6 PROGRAM OR TASK RESTART 182
- Vol. 3A 5-7 183
- 5.7.1 Handling Multiple NMIs 184
- Vol. 3A 5-9 185
- INTERRUPTS 186
- 5-12 Vol. 3A 188
- • Task-gate descriptor 189
- • Interrupt-gate descriptor 189
- • Trap-gate descriptor 189
- 5-16 Vol. 3A 192
- 5-18 Vol. 3A 194
- 5.12.2 Interrupt Tasks 195
- 5.13 ERROR CODE 197
- 5.14.1 64-Bit Mode IDT 198
- Vol. 3A 5-23 199
- 5.14.3 IRET in IA-32e Mode 200
- 5.14.5 Interrupt Stack Table 201
- 5-26 Vol. 3A 202
- Vol. 3A 5-27 203
- Interrupt 2—NMI Interrupt 205
- 5-30 Vol. 3A 206
- Vol. 3A 5-31 207
- 5-32 Vol. 3A 208
- Vol. 3A 5-33 209
- 5-34 Vol. 3A 210
- Vol. 3A 5-35 211
- 5-36 Vol. 3A 212
- Vol. 3A 5-39 215
- Exception Class Fault 216
- Description 216
- 5-42 Vol. 3A 218
- Vol. 3A 5-43 219
- 5-44 Vol. 3A 220
- Vol. 3A 5-45 221
- 5-46 Vol. 3A 222
- Vol. 3A 5-47 223
- 5-48 Vol. 3A 224
- Vol. 3A 5-49 225
- 5-50 Vol. 3A 226
- Vol. 3A 5-51 227
- MOV SS, AX 229
- MOV SP, StackTop 229
- 5-54 Vol. 3A 230
- Vol. 3A 5-55 231
- 5-56 Vol. 3A 232
- 5-58 Vol. 3A 234
- Vol. 3A 5-59 235
- 5-60 Vol. 3A 236
- Vol. 3A 5-61 237
- Vol. 3A 5-63 239
- 5-64 Vol. 3A 240
- Task Management 241
- CHAPTER 6 243
- TASK MANAGEMENT 243
- 6.1.2 Task State 244
- 6.1.3 Executing a Task 245
- • Task-state segment (TSS) 246
- • TSS descriptor 246
- • Task register 246
- 6.2.2 TSS Descriptor 249
- 6.2.4 Task Register 251
- Figure 6-5. Task Register 252
- 6.2.5 Task-Gate Descriptor 253
- 6.3 TASK SWITCHING 254
- 6.4 TASK LINKING 258
- Figure 6-8. Nested Tasks 259
- 6.4.2 Modifying Task Linkages 260
- 6.5 TASK ADDRESS SPACE 261
- Multiple-Processor 267
- Management 267
- CHAPTER 7 269
- MULTIPLE-PROCESSOR MANAGEMENT 269
- 7.1 LOCKED ATOMIC OPERATIONS 270
- 7.1.2 Bus Locking 271
- 7-6 Vol. 3A 274
- 7.2 MEMORY ORDERING 275
- 7.4 SERIALIZING INSTRUCTIONS 282
- 7.5.1 BSP and AP Processors 284
- Vol. 3A 7-19 287
- 7-20 Vol. 3A 288
- • Cores per Package 292
- 7.8 INTEL 294
- HYPER-THREADING TECHNOLOGY 294
- ARCHITECTURE 294
- 7.8.2 APIC Functionality 296
- 7.8.8 IA32_MISC_ENABLE MSR 298
- 7.8.9 Memory Ordering 298
- 7.8.12 Self Modifying Code 299
- 7.9 DUAL-CORE ARCHITECTURE 301
- 7.9.4 IA32_MISC_ENABLE MSR 302
- Platform 304
- Hyper-Threading Technology 305
- 7-38 Vol. 3A 306
- Vol. 3A 7-39 307
- 7-40 Vol. 3A 308
- Vol. 3A 7-41 309
- 7-42 Vol. 3A 310
- Vol. 3A 7-43 311
- 7-44 Vol. 3A 312
- 7.11.1 HLT Instruction 313
- 7.11.2 PAUSE Instruction 314
- Spin_Lock: 317
- JE Get_Lock 317
- 7-50 Vol. 3A 318
- Vol. 3A 7-51 319
- 7-52 Vol. 3A 320
- Advanced 323
- Programmable 323
- Interrupt Controller 323
- CHAPTER 8 325
- ADVANCED PROGRAMMABLE 325
- INTERRUPT CONTROLLER (APIC) 325
- 8-2 Vol. 3A 326
- 3-Wire APIC Bus 327
- MP systems 328
- 8.2 SYSTEM BUS VS. APIC BUS 329
- 8.3 THE INTEL 329
- 82489DX EXTERNAL APIC 329
- THE APIC, AND THE XAPIC 329
- 8.4 LOCAL APIC 329
- 8-6 Vol. 3A 330
- 8-10 Vol. 3A 334
- 63 071011 8912 335
- 8.4.6 Local APIC ID 336
- 8.4.7 Local APIC State 336
- Vol. 3A 8-13 337
- 8-14 Vol. 3A 338
- 8.5 HANDLING LOCAL INTERRUPTS 339
- 8.5.1 Local Vector Table 339
- Vol. 3A 8-17 341
- 8.5.2 Valid Interrupt Vectors 342
- 8.5.3 Error Handling 343
- 8.5.4 APIC Timer 344
- 8-22 Vol. 3A 346
- 8-24 Vol. 3A 348
- Vol. 3A 8-25 349
- 8-28 Vol. 3A 352
- 8-30 Vol. 3A 354
- 8-32 Vol. 3A 356
- 8.8 HANDLING INTERRUPTS 357
- Processors 357
- Pentium Processors) 359
- vector / 16 360
- Figure 8-21. EOI Register 364
- 8.9 SPURIOUS INTERRUPT 365
- 8.10.1 Bus Message Formats 367
- 8-44 Vol. 3A 368
- 31 20 19 12 11 4 3 2 1 0 368
- Vol. 3A 8-45 369
- 8-46 Vol. 3A 370
- 31 16 15 14 13 11 10 8 7 0 370
- Vol. 3A 8-47 371
- 8-48 Vol. 3A 372
- Processor 373
- Management and 373
- Initialization 373
- CHAPTER 9 375
- PROCESSOR MANAGEMENT AND 375
- INITIALIZATION 375
- 9-2 Vol. 3A 376
- 9.2 X87 FPU INITIALIZATION 380
- 9.3 CACHE ENABLING 382
- Vol. 3A 9-9 383
- OPERATION 384
- 9.7.1 Real-Address Mode IDT 385
- 9.7.2 NMI Interrupt Handling 385
- 9-12 Vol. 3A 386
- 9.8.3 Initializing Paging 387
- 9-14 Vol. 3A 388
- Vol. 3A 9-15 389
- 9-16 Vol. 3A 390
- 9.9 MODE SWITCHING 391
- 9-18 Vol. 3A 392
- Vol. 3A 9-19 393
- 9-20 Vol. 3A 394
- FFFF FFFFH 395
- FFFF FFF0H 395
- FFFF 0000H 395
- 64K EPROM 395
- 9.10.1 Assembler Usage 396
- 9.10.2 STARTUP.ASM Listing 397
- 9-24 Vol. 3A 398
- Vol. 3A 9-25 399
- 9-26 Vol. 3A 400
- Vol. 3A 9-27 401
- 9-28 Vol. 3A 402
- Vol. 3A 9-29 403
- 162-172 of List File) 404
- RAM_START 405
- 9.10.3 MAIN.ASM Source Code 407
- 9.10.4 Supporting Files 407
- 9-34 Vol. 3A 408
- 9.11.1 Microcode Update 410
- Vol. 3A 9-41 415
- Table 9-10. Processor Flags 416
- Vol. 3A 9-43 417
- ; Offset of microcode update 418
- Vol. 3A 9-45 419
- 9-46 Vol. 3A 420
- Vol. 3A 9-47 421
- Access: Read/Write 421
- Vol. 3A 9-49 423
- 9-50 Vol. 3A 424
- Vol. 3A 9-51 425
- 9-52 Vol. 3A 426
- Vol. 3A 9-53 427
- 9-58 Vol. 3A 432
- Vol. 3A 9-59 433
- 9-60 Vol. 3A 434
- Table 9-16. Mnemonic Values 435
- Memory Cache 439
- CHAPTER 10 441
- MEMORY CACHE CONTROL 441
- 10.2 CACHING TERMINOLOGY 444
- 10.3.2 Choosing a Memory Type 449
- 10.4 CACHE CONTROL PROTOCOL 450
- 10.5 CACHE CONTROL 450
- and P6 family 452
- Pentium II Processors 456
- 10.5.3 Preventing Caching 458
- 10.6 SELF-MODIFYING CODE 461
- AND P6 FAMILY PROCESSORS) 462
- 10.8 EXPLICIT CACHING 462
- 10.10 STORE BUFFER 464
- Register Pair 471
- Vol. 3A 10-33 473
- 10-34 Vol. 3A 474
- 10.11.5 MTRR Initialization 475
- ≠ FirstType 476
- Vol. 3A 10-37 477
- 10-38 Vol. 3A 478
- 10.12.2 IA32_CR_PAT MSR 482
- 10.12.4 Programming the PAT 483
- Technology 487
- System Programming 487
- CHAPTER 11 489
- MMX™ TECHNOLOGY SYSTEM 489
- PROGRAMMING 489
- REGISTERS 492
- • System exceptions: 493
- Exceptions 494
- 11.6 DEBUGGING MMX CODE 494
- 11-8 Vol. 3A 496
- SSE, SSE2 and SSE3 497
- CHAPTER 12 499
- • CPUID.1:EDX.SSE[bit 25] = 1 500
- • CPUID.1:ECX.SSE3[bit 0] = 1 500
- SSE3, EM, MP, and TS 501
- • Memory Access Exceptions: 502
- Vol. 3A 12-5 503
- 12-6 Vol. 3A 504
- OR CONTEXT SWITCHES 505
- CONTEXT SWITCHES 505
- 12-8 Vol. 3A 506
- • Clears the TS flag 508
- Power and Thermal 509
- CHAPTER 13 511
- POWER AND THERMAL MANAGEMENT 511
- IA32_MPERF (Addr: E7H) 512
- IA32_APERF (Addr: E8H) 512
- Vol. 3A 13-3 513
- MANAGEMENT 514
- 13.4.2 Thermal Monitor 516
- Thermal Status Log 518
- Clock Modulation Facilities 521
- 16222327 522
- 16222324 523
- Machine Check 525
- Architecture 525
- CHAPTER 14 527
- MACHINE-CHECK ARCHITECTURE 527
- 14.3 MACHINE-CHECK MSRS 528
- . . . . 531
- 14.3.3 Mapping of the Pentium 537
- 14-12 Vol. 3A 538
- 14.6.1 Simple Error Codes 539
- 14.6.2 Compound Error Codes 540
- Vol. 3A 14-19 545
- 14.7.3 Pentium 546
- Vol. 3A 14-21 547
- 8086 Emulation 549
- CHAPTER 15 551
- 8086 EMULATION 551
- 15.2 VIRTUAL-8086 MODE 557
- 15.2.7 Sensitive Instructions 564
- 15.2.8 Virtual-8086 Mode I/O 564
- IN VIRTUAL-8086 MODE 565
- Mixing 16-Bit 579
- CHAPTER 16 581
- MIXING 16-BIT AND 32-BIT CODE 581
- 16.4.4 Parameter Translation 588
- IA-32 Architecture 591
- Compatibility 591
- CHAPTER 17 593
- 17.2. RESERVED BITS 594
- THROUGH SOFTWARE 594
- 17.5. INTEL MMX TECHNOLOGY 595
- 17.10. DUAL-CORE TECHNOLOGY 596
- PROCESSORS 596
- 17.13. OBSOLETE INSTRUCTIONS 598
- 17.14. UNDEFINED OPCODES 598
- 17.16. STACK OPERATIONS 599
- 17.16.1 PUSH SP 599
- 17.17. X87 FPU 600
- 17.17.2 x87 FPU Status Word 601
- 17.17.3 x87 FPU Control Word 602
- 17.17.4 x87 FPU Tag Word 602
- 17.17.5 Data Types 602
- Vol. 3A 17-11 603
- 17-12 Vol. 3A 604
- Vol. 3A 17-13 605
- 17-14 Vol. 3A 606
- Vol. 3A 17-15 607
- 17-16 Vol. 3A 608
- Vol. 3A 17-17 609
- 17.17.9 Obsolete Instructions 610
- Vol. 3A 17-19 611
- 17.20. CONTROL REGISTERS 613
- 17-22 Vol. 3A 614
- Vol. 3A 17-23 615
- 17.22. DEBUG FACILITIES 616
- Vol. 3A 17-25 617
- 17-26 Vol. 3A 618
- 17.25. INTERRUPTS 619
- 17.25.2 NMI Interrupts 619
- 17.25.3 IDT Limit 620
- Family and Pentium Processors 621
- 17.27. TASK SWITCHING AND TSS 621
- 17.27.2 TSS Selector Writes 622
- Offset FH from beginning of 623
- 17-32 Vol. 3A 624
- 17.29. PAGING 625
- 17.29.1 Large Pages 625
- 17.29.2 PCD and PWT Flags 625
- 17.30. STACK OPERATIONS 626
- 17.30.2 Error Code Pushes 627
- 17.32.1 Segment Wraparound 628
- Vol. 3A 17-37 629
- 17.34. BUS LOCKING 630
- 17.35. BUS HOLD 631
- 17-40 Vol. 3A 632
- Vol. 3A 17-41 633
- 17-42 Vol. 3A 634
- INTEL SALES OFFICES 635
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