Re: [PATCH v3 3/4] KVM: x86: Virtualize AMD CPUID faulting

[Jim Mattson]

On Thu, May 14, 2026 at 9:35 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Thu, May 14, 2026, Jim Mattson wrote:
> > On Thu, May 14, 2026 at 9:20 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> > > Oooh, this is based on the generic CPL rules.  I didn't think about it from that
> > > perspective.  So yeah, addressing that does make sense.  What a pain.
> >
> > When I fix this in version 4, what's the correct footer for Sashiko attribution:
> >
> > Assisted-by: Sashiko:gemini/gemini-3.1-pro-preview
> >
> > or
> >
> > Reported-by: Sashiko:gemini/gemini-3.1-pro-preview
>
> This, or even just:
>
>   Reported-by: Sashiko
>
> is good enough for me.  I don't expect random developers to know or care what
> model was used, at least not when it comes to reporting bugs.  If you use AI to
> help write the code, then maybe I'd care?

I had Jetski write an empirical test to see how the hardware behaves.
On the first userspace CPUID VM-exit, temporarily set #GP on userspace
CPUID per the appropriate vendor's mechanism, make sure that we
intercept #GP, and re-enter the guest without advancing RIP. Then, see
what the next VM-exit is.

Surprise!

kvm_intel: KVM: EMPIRICAL TEST RESULT: #GP took precedence over CPUID VM-exit
kvm_amd: KVM: EMPIRICAL TEST RESULT (SVM): CPUID VM-exit took
precedence over #GP!

LOL!

David: Is this intentional or a bug?