Re: [Qemu-devel] [PATCH v3] target-i386/cpu: Add new EPYC CPU model

[Brijesh Singh <brijesh.singh@amd.com>]

Hi Paolo,

On 08/17/2017 11:45 AM, Paolo Bonzini wrote:
> On 15/08/2017 19:00, Brijesh Singh wrote:
>>
>> The following features bits have been added/removed compare to Opteron_G5
>>
>> Added: monitor, movbe, rdrand, mmxext, ffxsr, rdtscp, cr8legacy, osvw,
>>         fsgsbase, bmi1, avx2, smep, bmi2, rdseed, adx, smap, clfshopt, sha
>>         xsaveopt, xsavec, xgetbv1, arat
>>
>> Removed: xop, fma4, tbm
> 
> Interesting, why were these removed?
> 

I don't know exact reason why these were removed - I am going with whatever is
listed as supported feature bit in PPR [1], but I will ask around and let you
know. I believe some of these instruction are superseded with newer instructions
(e.g fma4->fma)

[1] http://support.amd.com/TechDocs/54945_PPR_Family_17h_Models_00h-0Fh.pdf


> Do we want to add "topoext" support too?  What about mwaitx?
> 

Looking at PPR I think we can safely enable "topoext" - it is listed as fixed to 1
but "mwaitx" support depends on the MSR condition. If host BIOS does not set the MSR
then we may not able to use "mwaitx" feature.

Actually, I was trying to ensure that in this patch I do not use a feature which is not
supported by KVM. Looking at kvm_cpuid_8000_0001_ecx_x86_features [2] hinted me that
both "topoext" and "mwaitx" was not supported hence I skipped it. I can add comment to
remind us.

http://elixir.free-electrons.com/linux/latest/source/arch/x86/kvm/cpuid.c#L360

-Brijesh