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

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Message-ID: <1320676467.18053.43.camel@twins>
Date:	Mon, 07 Nov 2011 15:34:27 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	kvm@...r.kernel.org, avi@...hat.com, 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 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?
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