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

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Message-ID: <0d9d6900-9197-48fa-9627-8a9231b3857e@amd.com>
Date:   Thu, 7 Dec 2023 11:42:08 +0530
From:   "Nikunj A. Dadhania" <nikunj@....com>
To:     Dionna Amalie Glaze <dionnaglaze@...gle.com>
Cc:     linux-kernel@...r.kernel.org, thomas.lendacky@....com,
        x86@...nel.org, kvm@...r.kernel.org, bp@...en8.de,
        mingo@...hat.com, tglx@...utronix.de, dave.hansen@...ux.intel.com,
        pgonda@...gle.com, seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v6 12/16] x86/sev: Prevent RDTSC/RDTSCP interception for
 Secure TSC enabled guests

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