DOS ain't dead

Option limit cpuid maximum in bios. (Miscellaneous)

posted by Japheth , Germany (South), 30.11.2020, 04:13

There's the

IA32_MISC_ENABLE MSR (1A0h), bit 22

for Intel, but according to Intel docs it allows to reduce cpuid max to 2 only.


When this bit is set to 1, CPUID.00H returns
a maximum value in EAX[7:0] of 2.
BIOS should contain a setup question that
allows users to specify when the installed
OS does not support CPUID functions
greater than 2.
Before setting this bit, BIOS must execute
the CPUID.0H and examine the maximum
value returned in EAX[7:0]. If the maximum
value is greater than 2, this bit is
supported.
Otherwise, this bit is not supported. Setting
this bit when the maximum value is not
greater than 2 may generate a #GP
exception.
Setting this bit may cause unexpected
behavior in software that depends on the
availability of CPUID leaves greater than 2.

---
MS-DOS forever!

Complete thread:

• Option limit cpuid maximum in bios. - CandyMan, 30.11.2020, 01:42 (Miscellaneous)
  • Option limit cpuid maximum in bios. - Japheth, 30.11.2020, 04:13
    • Option limit cpuid maximum in bios. - CandyMan, 30.11.2020, 11:41