linux-kernel - Re: [PATCH v4 06/16] KVM: x86/pmu: Reprogram guest PEBS event to emulate guest PEBS counter

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Message-ID: <YG1v4KFCPSoKcoyd@hirez.programming.kicks-ass.net>
Date:   Wed, 7 Apr 2021 10:40:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Like Xu <like.xu@...ux.intel.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>, eranian@...gle.com,
        andi@...stfloor.org, kan.liang@...ux.intel.com,
        wei.w.wang@...el.com, Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v4 06/16] KVM: x86/pmu: Reprogram guest PEBS event to
 emulate guest PEBS counter

On Mon, Mar 29, 2021 at 01:41:27PM +0800, Like Xu wrote:

> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 827886c12c16..3509b18478b9 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -74,11 +74,20 @@ static void kvm_perf_overflow_intr(struct perf_event *perf_event,
>  {
>  	struct kvm_pmc *pmc = perf_event->overflow_handler_context;
>  	struct kvm_pmu *pmu = pmc_to_pmu(pmc);
> +	bool skip_pmi = false;
>  
>  	if (!test_and_set_bit(pmc->idx, pmu->reprogram_pmi)) {
> -		__set_bit(pmc->idx, (unsigned long *)&pmu->global_status);
> +		if (perf_event->attr.precise_ip) {
> +			/* Indicate PEBS overflow PMI to guest. */
> +			skip_pmi = test_and_set_bit(GLOBAL_STATUS_BUFFER_OVF_BIT,
> +				(unsigned long *)&pmu->global_status);

Is there actual concurrency here, or did you forget to type __?

And in case you're using vim, use something like: set cino=(0:0

> +		} else
> +			__set_bit(pmc->idx, (unsigned long *)&pmu->global_status);
>  		kvm_make_request(KVM_REQ_PMU, pmc->vcpu);
>  
> +		if (skip_pmi)
> +			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