[Bug]: SDM 092 CPUID typo

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Domain
documentation

Research direction

Start by locating SDM Vol. 1 table 21-1, page 21-3, in section 21.1.5 and inspect the 8000_0001h CPUID entry. Verify the field against AMD APM Vol. 3, Appendix E, page 650, then correct the bit position and confirm that the displayed table distinguishes EDX[11] from the NX bit at EDX[20].

Written by the indexing model from the issue text.

Description

SDM PDF issue

SDM 092 Vol 1 table 21-1 on page 21-3 (441 of 600) in section 21.1.5 lists mutable CPUID fields.

For 8000_0001h it shows EDX[20] as SYSCALL_SYSRET_64.

That bit position is incorrect.

The correct bit is EDX[11]. (By contrast, EDX[20] is the NX bit.)

The authoritative source is AMD's APM Vol 3, July 2026, #24594-3.38, page 650 (692 of 728) in Appendix E.

(For historic completeness: AMD K6 processors with model 6 used bit 10; starting with model 7, bit 11 was used instead. If need be, I can elaborate on why that change happened.)

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