Re: [PATCH v6 12/16] x86/sev: Prevent RDTSC/RDTSCP interception for Secure TSC enabled guests

[Nikunj A. Dadhania]

On 12/7/2023 12:15 AM, Dionna Amalie Glaze wrote:
>>>> +       if (sev_status & MSR_AMD64_SNP_SECURE_TSC)
>>>> +               return ES_VMM_ERROR;
>>>
>>> Is this not a cc_platform_has situation? I don't recall how the
>>> conversation shook out for TDX's forcing X86_FEATURE_TSC_RELIABLE
>>> versus having a cc_attr_secure_tsc
>>
>> For SNP, SecureTSC is an opt-in feature. AFAIU, for TDX the feature is
>> turned on by default. So SNP guests need to check if the VMM has enabled
>> the feature before moving forward with SecureTSC initializations.
>>
>> The idea was to have some generic name instead of AMD specific SecureTSC
>> (cc_attr_secure_tsc), and I had sought comments from Kirill [1]. After
>> that discussion I have added a synthetic flag for Secure TSC[2].
>>
> 
> So with regards to [2], this sev_status flag check should be
> cpu_has_feature(X86_FEATURE_SNP_SECURE_TSC)? I'm not sure if that's
> available in early boot where this code is used, so if it isn't,
> probably that's worth a comment.

Right, I will update the comment.

Regards
Nikunj