Re: [PATCH] KVM: x86/pmu: Don't retry a counter whose config was rejected

[Sean Christopherson <seanjc@google.com>]

On Fri, Sep 18, 2026, Luka Absandze wrote:
> On 2026-09-18 09:16, Sean Christopherson wrote:
> > Hmm, would it instead make more sense to explicitly check for -EBUSY?  -EINVAL
> > isn't the only fatal error code.
> > 
> > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> > index a7d60c8785cd..5296ee8f32af 100644
> > --- a/arch/x86/kvm/pmu.c
> > +++ b/arch/x86/kvm/pmu.c
> > @@ -681,7 +681,7 @@ void kvm_pmu_handle_event(struct kvm_vcpu *vcpu)
> >                  * PMU refresh.  Don't make a new request as doing so can stall
> >                  * the guest if reprogramming repeatedly fails.
> >                  */
> > -               if (reprogram_counter(pmc))
> > +               if (reprogram_counter(pmc) == -EBUSY)
> >                         set_bit(pmc->idx, pmu->reprogram_pmi);
> >         }
> > 
> > Though I guess one could argue -ENOMEM is also transient?
> 
> I had contemplated this, but could not convince myself at a glance that
> perf and KVM agreed on what constituted a transient error.
> I have now concluded I was seeing ghosts :)
> 
> > E.g. this? (completely untested)
> > [diff]
> 
> Tested against the fault described in the linked patch and selftests on
> AMD Zen 3 (although I don't think there's much coverage in this regard).
> 
> If no other objections, would you be fine with taking the diff you
> provided into the tree or would you prefer a v2?

Go ahead and send a v2, I want to see what Sashiko thinks.