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

[Sean Christopherson <seanjc@google.com>]

On Tue, Jun 25, 2024, Jim Mattson wrote:
> On Mon, Jun 17, 2024 at 11:29 AM Maxim Levitsky <mlevitsk@redhat.com> 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@google.com
> > >
> >
> > This works for me.
> > Thanks,
> >
> > Best regards,
> >         Maxim Levitsky
> 
> Sean and/or Paolo,
> 
> I'm still waiting for this to show up. :)

13a12056be1e4939dadbd0d2cfb65df400832905 x86: msr: testing MSR_IA32_FLUSH_CMD reserved bits only in KVM emulation
51b87946279cf6e9248ceacf0f27833b6ebeef5e x86: Add FEP support on read/write register instructions

/drop mic