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

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Message-ID: <87o7szouyr.fsf@ovpn-194-185.brq.redhat.com>
Date:   Tue, 22 Nov 2022 16:43:56 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, 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

Sean Christopherson <seanjc@...gle.com> writes:

> 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>
>

I completely forgot about this one! Any chance it can still be queueed
for 6.2? Thanks!

-- 
Vitaly