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

Dionna Amalie Glaze
2023-12-06T18:45:47Z

> >> + 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.

--
-Dionna Glaze, PhD (she/her)