linux-kernel - Re: [PATCH v4 23/38] KVM: x86/pmu: Configure the interception of PMU MSRs

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Message-ID: <059f5886-e7df-4067-be38-8aca7750059a@linux.intel.com>
Date: Mon, 19 May 2025 13:18:46 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Mingwei Zhang <mizhang@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>,
 Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>, Liang@...gle.com,
 Kan <kan.liang@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
 Yongwei Ma <yongwei.ma@...el.com>,
 Xiong Zhang <xiong.y.zhang@...ux.intel.com>,
 Jim Mattson <jmattson@...gle.com>, Sandipan Das <sandipan.das@....com>,
 Zide Chen <zide.chen@...el.com>, Eranian Stephane <eranian@...gle.com>,
 Shukla Manali <Manali.Shukla@....com>,
 Nikunj Dadhania <nikunj.dadhania@....com>
Subject: Re: [PATCH v4 23/38] KVM: x86/pmu: Configure the interception of PMU
 MSRs

On 5/16/2025 9:34 PM, Sean Christopherson wrote:
> On Mon, Mar 24, 2025, Mingwei Zhang wrote:
>> +static void amd_pmu_update_msr_intercepts(struct kvm_vcpu *vcpu)
>> +{
>> +	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>> +	struct vcpu_svm *svm = to_svm(vcpu);
>> +	int msr_clear = !!(kvm_mediated_pmu_enabled(vcpu));
>> +	int i;
>> +
>> +	for (i = 0; i < min(pmu->nr_arch_gp_counters, AMD64_NUM_COUNTERS); i++) {
>> +		/*
>> +		 * Legacy counters are always available irrespective of any
>> +		 * CPUID feature bits and when X86_FEATURE_PERFCTR_CORE is set,
>> +		 * PERF_LEGACY_CTLx and PERF_LEGACY_CTRx registers are mirrored
>> +		 * with PERF_CTLx and PERF_CTRx respectively.
>> +		 */
>> +		set_msr_interception(vcpu, svm->msrpm, MSR_K7_EVNTSEL0 + i, 0, 0);
> This is pointless.  Simply do nothing and KVM will always intercept event selectors.

Yes.