Re: [PATCH 2/6] x86: KVM: Enable AMX-FP16 CPUID and expose it to guest

Jiaxi Chen
2022-11-03T02:38:46Z

On 11/3/2022 2:21 AM, Dave Hansen wrote:
> On 11/2/22 11:16, Paolo Bonzini wrote:
>> On 11/2/22 19:14, Dave Hansen wrote:
>>>>         kvm_cpu_cap_mask(CPUID_7_1_EAX,
>>>> -        F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD)
>>>> +        F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD) | F(AMX_FP16)
>>>>       );
>>>>         kvm_cpu_cap_mask(CPUID_D_1_EAX,
>>>
>>> KVM folks, is the idea that every feature that is enumerated to a guest
>>> needs to be in one of these masks?  Or is there something special about
>>> the features in these masks?
>>
>> Yes, all features are vetted manually to see whether they require new
>> MSRs and the like.  Therefore, anything that userspace can set in the
>> guest's CPUID must be in the list.
>
> Makes sense.
>
> Intel folks, when you add these bits, can you please include information
> about the "vetting" that you performed?
>
> For example, it would be handy to say:
>
> AMX_FP16 is just a new instruction that operates on existing AMX
> tile registers. It needs no additional enabling on top of the
> existing kernel AMX enabling.

Thanks for Dave's suggestion. It makes the commit message much clear
and readable. Will modify it in v2.

--
Regards,
Jiaxi