linux-kernel - Re: [PATCH 4/4] KVM: x86/pmu: Refactoring kvm_perf_overflow{

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Message-ID: <0008cb01-9100-6664-2cb8-e1c741f69a77@redhat.com>
Date:   Thu, 18 Nov 2021 15:53:30 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Like Xu <like.xu.linux@...il.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] KVM: x86/pmu: Refactoring kvm_perf_overflow{_intr}()

On 11/16/21 13:20, Like Xu wrote:
> -	}
> +	if (!intr)
> +		return;
> +
> +	/*
> +	 * 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 wasn't executing hlt instruction at the
> +	 * time of vmexit and is not going to re-enter guest mode until
> +	 * woken up. So we should wake it, but this is impossible from
> +	 * NMI context. Do it from irq work instead.
> +	 */
> +	if (!kvm_is_in_guest())
> +		irq_work_queue(&pmc_to_pmu(pmc)->irq_work);
> +	else
> +		kvm_make_request(KVM_REQ_PMI, pmc->vcpu);
> +}
> +
> +static void kvm_perf_overflow(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_to_pmu(pmc);
> +
> +	if (!test_and_set_bit(pmc->idx, pmu->reprogram_pmi))
> +		kvm_pmu_counter_overflow(pmc, need_overflow_intr(pmc));
>   }

It could be even better to make a single function, but instead of 
need_overflow_intr(pmc) you should store into pmc from 
pmc_reprogram_counter.  Like this:

	/* Ignore counters that have been reported already.  */
	if (test_and_set_bit(pmc->idx, pmu->reprogram_pmi))
		return;

	__set_bit(pmc->idx, (unsigned long *)&pmu->global_status);
	kvm_make_request(KVM_REQ_PMU, pmc->vcpu);

	if (pmc->intr) {
		/*
		 * 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 wasn't executing hlt instruction at the
		 * time of vmexit and is not going to re-enter guest mode until
		 * woken up. So we should wake it, but this is impossible from
		 * NMI context. Do it from irq work instead.
		 */
		if (!kvm_is_in_guest())
			irq_work_queue(pmu->irq_work);
		else
			kvm_make_request(KVM_REQ_PMI, pmc->vcpu);
	}

Paolo