linux-kernel - Re: [PATCHv2 2/9] KVM: Expose a version 2 architectural PMU to a guests

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Date:	Mon, 07 Nov 2011 16:46:39 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Gleb Natapov <gleb@...hat.com>, kvm@...r.kernel.org,
	mtosatti@...hat.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
	acme@...stprotocols.net
Subject: Re: [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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