Re: [edk2-devel] [PATCH 1/2] UefiCpuPkg/MpInitLib: Use AsmCpuidEx() for CPUID_EXTENDED_TOPOLOGY leaf

["Lendacky, Thomas via groups.io" <thomas.lendacky=amd.com@groups.io>]

On 11/28/23 08:35, Lendacky, Thomas via groups.io wrote:
> On 11/6/23 17:15, Tom Lendacky wrote:
>> On 11/6/23 16:45, Lendacky, Thomas via groups.io wrote:
>>> The CPUID_EXTENDED_TOPOLOGY CPUID leaf takes a subleaf as input when
>>> returning CPUID information. However, the AsmCpuid() function does not
>>> zero out ECX before the CPUID instruction, so the input leaf is used as
>>> the sub-leaf for the CPUID request and returns erroneous/invalid CPUID
>>> data, since the intent of the request was to get data related to sub-leaf
>>> 0. Instead, use AsmCpuidEx() for the CPUID_EXTENDED_TOPOLOGY leaf.
>>
>> Alternatively, the AsmCpuid() function could be changed to XOR ECX 
>> before invoking the CPUID instruction. This would ensure that the 0 
>> sub-leaf is returned for any CPUID leaves that support sub-leaves. 
>> Thoughts?
>>
>> Adding some additional maintainers for their thoughts, too.
> 
> Any thoughts on this approach (as a separate, unrelated patch) to 
> eliminate future issues that could pop up?
> 
> Seems like zeroing out ECX before calling CPUID would be an appropriate 
> thing to do, but I'm not sure if that will have any impact on the existing 
> code base... it shouldn't, but you never know.

Just a re-ping for thoughts on this.

Thanks,
Tom

> 
> Thanks,
> Tom
> 
>>
>> Thanks,
>> Tom


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