Re: [PATCH v3 00/17] KVM: x86/pmu: Add support to enable Guest PEBS via DS

[Andi Kleen]

On Fri, Jan 15, 2021 at 10:51:38AM -0800, Sean Christopherson wrote:
> On Fri, Jan 15, 2021, Andi Kleen wrote:
> > > I'm asking about ucode/hardare.  Is the "guest pebs buffer write -> PEBS PMI"
> > > guaranteed to be atomic?
> > 
> > Of course not.
> 
> So there's still a window where the guest could observe the bad counter index,
> correct?

Yes.

But with single record PEBS it doesn't really matter with normal perfmon
drivers.

-Andi