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SubjectRe: [PATCHv2 2/9] KVM: Expose a version 2 architectural PMU to a guests
On 11/07/2011 04:34 PM, Peter Zijlstra wrote:
> On Thu, 2011-11-03 at 14:33 +0200, Gleb Natapov wrote:
> > +static void kvm_perf_overflow_intr(struct perf_event *perf_event,
> > + struct perf_sample_data *data, struct pt_regs *regs)
> > +{
> > + struct kvm_pmc *pmc = perf_event->overflow_handler_context;
> > + struct kvm_pmu *pmu = &pmc->vcpu->arch.pmu;
> > + if (!test_and_set_bit(pmc->idx, (unsigned long *)&pmu->reprogram_pmi)) {
> > + kvm_perf_overflow(perf_event, data, regs);
> > + kvm_make_request(KVM_REQ_PMU, pmc->vcpu);
> > + /*
> > + * Inject PMI. If vcpu was in a guest mode during NMI PMI
> > + * can be ejected on a guest mode re-entry. Otherwise we can't
> > + * be sure that vcpu is not halted, so we should kick it, but
> > + * this is impossible from NMI context. Do it from irq work
> > + * instead.
> > + */
> > + if (!kvm_is_in_guest())
> > + irq_work_queue(&pmc->vcpu->arch.pmu.irq_work);
> > + else
> > + kvm_make_request(KVM_REQ_PMI, pmc->vcpu);
> > + }
> > +}
>
> I'm not sure I get this, since the counters are vcpu task bound and only
> count while the guest is running as per (144d31e6f19) how can we get an
> NMI outside of guest context with the vcpu not halted?

PMI skew. Do we know how bad it can get?

--
error compiling committee.c: too many arguments to function



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