Re: [PATCH v7 26/26] KVM: selftest: Add a selftest for VMRUN/#VMEXIT with unmappable vmcb12

[Yosry Ahmed]

On Fri, Mar 6, 2026 at 8:35 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Fri, Mar 06, 2026, Yosry Ahmed wrote:
> > > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> > > index b191c6cab57d..78a542c6ddf1 100644
> > > --- a/arch/x86/kvm/svm/nested.c
> > > +++ b/arch/x86/kvm/svm/nested.c
> > > @@ -1105,10 +1105,8 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
> > >
> > >         vmcb12_gpa = svm->vmcb->save.rax;
> > >         err = nested_svm_copy_vmcb12_to_cache(vcpu, vmcb12_gpa);
> > > -       if (err == -EFAULT) {
> > > -               kvm_inject_gp(vcpu, 0);
> > > -               return 1;
> > > -       }
> > > +       if (err == -EFAULT)
> > > +               return kvm_handle_memory_failure(vcpu, X86EMUL_UNHANDLEABLE, NULL);
> >
> > Why not call kvm_prepare_emulation_failure_exit() directly?
>
> Mostly because my mental coin-flip came up heads.  But it's also one less line
> of code, woot woot!
>
> > Is the premise that kvm_handle_memory_failure() might evolve to do more
> > things for emulation failures that are specifically caused by memory
> > failures, other than potentially injecting an exception?
>
> Yeah, more or less.  I doubt kvm_handle_memory_failure() will ever actually evolve
> into anything more sophisticated, but at the very least, using
> kvm_handle_memory_failure() documents _why_ KVM can't handle emulation.

Yeah I agree with this too.

>
> On second thought, I think using X86EMUL_IO_NEEDED would be more appropriate.
> The memremap() is only reachable if allow_unsafe_mappings is enabled, and so for
> a "default" configuration, failure can only occur on:
>
>         if (is_error_noslot_pfn(map->pfn))
>                 return -EINVAL;
>
> Which doesn't _guarantee_ that emulated I/O is required, but we're definitely
> beyond splitting hairs at that point.