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SubjectRe: [PATCH 2/2] KVM: x86: introduce KVM_X86_QUIRK_TSC_HOST_ACCESS
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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 :)).

Paolo

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