linux-kernel - Re: [PATCH 1/2] KVM: SVM: Fix TSC

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Date:   Fri, 15 Sep 2023 11:52:35 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Babu Moger <babu.moger@....com>
Subject: Re: [PATCH 1/2] KVM: SVM: Fix TSC_AUX virtualization setup

On 9/14/23 15:48, Tom Lendacky wrote:
> On 9/14/23 15:28, Sean Christopherson wrote:
>> On Thu, Sep 14, 2023, Tom Lendacky wrote:

> 
>>
>>> +        if (guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
>>> +            svm_clr_intercept(svm, INTERCEPT_RDTSCP);
>>
>> Same thing here.
> 
> Will do.

For RDTSCP, svm_recalc_instruction_intercepts() will set/clear the RDTSCP 
intercept as part of the svm_vcpu_set_after_cpuid() path, but it will only 
do it based on kvm_cpu_cap_has(X86_FEATURE_RDTSCP) being true, which is 
very likely.

Do you think that is good enough and we can drop the setting and clearing 
of the RDTSCP intercept in the sev_es_vcpu_set_after_cpuid() function and 
only deal with the TSC_AUX MSR intercept?

On a side note, it looks like RDTSCP would not be intercepted if the KVM 
cap X86_FEATURE_RDTSCP feature is cleared, however unlikely, in 
kvm_set_cpu_caps() and RDTSCP is not advertised to the guest (assuming the 
guest is ignoring the RDTSCP CPUID bit).

Thanks,
Tom

> 
> Thanks,
> Tom
> 
>>
>>> +    }
>>> +}