Re: kvm selftest 'msr' fails on some skylake cpus

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On Mon, Jun 17, 2024 at 11:29 AM Maxim Levitsky <mlevitsk@xxxxxxxxxx> wrote:
>
> On Fri, 2024-06-14 at 07:26 -0700, Sean Christopherson wrote:
> > On Thu, Jun 13, 2024, Maxim Levitsky wrote:
> > > Hi!
> > >
> > > This kvm unit test tests that all reserved bits of the MSR_IA32_FLUSH_CMD #GP, but apparently
> > > on some systems this test fails.
> > >
> > > For example I reproduced this on:
> > >
> > > model name  : Intel(R) Xeon(R) CPU E3-1260L v5 @ 2.90GHz
> > > stepping    : 3
> > > microcode   : 0xf0
> > >
> > >
> > > As I see in the 'vmx_vcpu_after_set_cpuid', we passthough this msr to the guest AS IS,
> > > thus the unit test tests the microcode.
> > >
> > > So I suspect that the test actually caught a harmless microcode bug.
> >
> > Yeah, we encountered the same thing and came to the same conclusion.
> >
> > > What do you think we should do to workaround this? Maybe disable this check on
> > > affected cpus or turn it into a warning because MSR_IA32_FLUSH_CMD reserved bits
> > > test doesn't test KVM?
> >
> > Ya, Mingwei posted a patch[*] to force KVM to emulate the faulting accesses, which
> > more or less does exactly that, but preserves a bit of KVM coverage.  I'll get a
> > KUT pull request sent to Paolo today, I've got a sizeable number of changes ready.
> >
> > [*] https://lore.kernel.org/all/20240417232906.3057638-3-mizhang@xxxxxxxxxx
> >
>
> This works for me.
> Thanks,
>
> Best regards,
>         Maxim Levitsky

Sean and/or Paolo,

I'm still waiting for this to show up. :)





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