Re: [PATCH 2/2] KVM: x86: introduce KVM_X86_QUIRK_TSC_HOST_ACCESS

[Paolo Bonzini]

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@xxxxxxxxxx>
> > > Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> >
> > 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