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    SubjectRe: [PATCH 2/2] KVM: x86: introduce KVM_X86_QUIRK_TSC_HOST_ACCESS
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    On Mon, 2020-11-30 at 15:15 +0100, Paolo Bonzini wrote:
    > On 30/11/20 15:11, Maxim Levitsky wrote:
    > > On Mon, 2020-11-30 at 14:54 +0100, Paolo Bonzini wrote:
    > > > On 30/11/20 14:35, Maxim Levitsky wrote:
    > > > > This quirk reflects the fact that we currently treat MSR_IA32_TSC
    > > > > and MSR_TSC_ADJUST access by the host (e.g qemu) in a way that is different
    > > > > compared to an access from the guest.
    > > > >
    > > > > For host's MSR_IA32_TSC read we currently always return L1 TSC value, and for
    > > > > host's write we do the tsc synchronization.
    > > > >
    > > > > For host's MSR_TSC_ADJUST write, we don't make the tsc 'jump' as we should
    > > > > for this msr.
    > > > >
    > > > > When the hypervisor uses the new TSC GET/SET state ioctls, all of this is no
    > > > > longer needed, thus leave this enabled only with a quirk
    > > > > which the hypervisor can disable.
    > > > >
    > > > > Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
    > > > > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
    > > >
    > > > This needs to be covered by a variant of the existing selftests testcase
    > > > (running the same guest code, but different host code of course).
    > > Do you think that the test should go to the kernel's kvm unit tests,
    > > or to kvm-unit-tests project?
    >
    > The latter already has x86_64/tsc_msrs_test.c (which I created in
    > preparation for this exact change :)).

    I'll prepare a test then for it!

    Best regards,
    Maxim Levitsky
    >
    > Paolo
    >


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