linux-kernel - Re: [RFC PATCH 27/41] KVM: x86/pmu: Clear PERF

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Message-ID: <ZhhbJCGcJ6Rshkfk@google.com>
Date: Thu, 11 Apr 2024 14:50:28 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Xiong Zhang <xiong.y.zhang@...ux.intel.com>
Cc: pbonzini@...hat.com, peterz@...radead.org, mizhang@...gle.com, 
	kan.liang@...el.com, zhenyuw@...ux.intel.com, dapeng1.mi@...ux.intel.com, 
	jmattson@...gle.com, kvm@...r.kernel.org, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org, zhiyuan.lv@...el.com, eranian@...gle.com, 
	irogers@...gle.com, samantha.alt@...el.com, like.xu.linux@...il.com, 
	chao.gao@...el.com
Subject: Re: [RFC PATCH 27/41] KVM: x86/pmu: Clear PERF_METRICS MSR for guest

On Fri, Jan 26, 2024, Xiong Zhang wrote:
> From: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> 
> Since perf topdown metrics feature is not supported yet, clear
> PERF_METRICS MSR for guest.

Please rewrite with --verbose, I have no idea what MSR_PERF_METRICS, and thus no
clue why it needs to be zeroed when loading guest context, e.g. it's not passed
through, so why does it matter?

> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> ---
>  arch/x86/kvm/vmx/pmu_intel.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 4b4da7f17895..ad0434646a29 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -916,6 +916,10 @@ static void intel_restore_pmu_context(struct kvm_vcpu *vcpu)
>  	 */
>  	for (i = pmu->nr_arch_fixed_counters; i < kvm_pmu_cap.num_counters_fixed; i++)
>  		wrmsrl(MSR_CORE_PERF_FIXED_CTR0 + i, 0);
> +
> +	/* Clear PERF_METRICS MSR since guest topdown metrics is not supported yet. */
> +	if (kvm_caps.host_perf_cap & PMU_CAP_PERF_METRICS)
> +		wrmsrl(MSR_PERF_METRICS, 0);
>  }
>  
>  struct kvm_pmu_ops intel_pmu_ops __initdata = {
> -- 
> 2.34.1
>