linux-kernel - Re: [PATCH v5 0/7] KVM: x86: Hyper-V invariant TSC control feature

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Message-ID: <Y0nA0DCeh4IPmWMX@google.com>
Date:   Fri, 14 Oct 2022 20:04:32 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/7] KVM: x86: Hyper-V invariant TSC control feature

On Thu, Oct 13, 2022, Vitaly Kuznetsov wrote:
> Normally, genuine Hyper-V doesn't expose architectural invariant TSC
> (CPUID.80000007H:EDX[8]) to its guests by default. A special PV MSR
> (HV_X64_MSR_TSC_INVARIANT_CONTROL, 0x40000118) and corresponding CPUID
> feature bit (CPUID.0x40000003.EAX[15]) were introduced. When bit 0 of the
> PV MSR is set, invariant TSC bit starts to show up in CPUID. When the 
> feature is exposed to Hyper-V guests, reenlightenment becomes unneeded.
> 
> Note: strictly speaking, KVM doesn't have to have the feature as exposing
> raw invariant TSC bit (CPUID.80000007H:EDX[8]) also seems to work for
> modern Windows versions. The feature is, however, tiny and straitforward
> and gives additional flexibility so why not.
> 
> Vitaly Kuznetsov (7):
>   x86/hyperv: Add HV_EXPOSE_INVARIANT_TSC define
>   KVM: x86: Add a KVM-only leaf for CPUID_8000_0007_EDX
>   KVM: x86: Hyper-V invariant TSC control
>   KVM: selftests: Rename 'msr->available' to 'msr->fault_exepected' in
>     hyperv_features test
>   KVM: selftests: Convert hyperv_features test to using
>     KVM_X86_CPU_FEATURE()
>   KVM: selftests: Test that values written to Hyper-V MSRs are preserved
>   KVM: selftests: Test Hyper-V invariant TSC control

For the series, in case Paolo ends up grabbing this:

Reviewed-by: Sean Christopherson <seanjc@...gle.com>