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

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Date: Sat, 13 Apr 2024 11:29:55 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>,
 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, 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 4/12/2024 5:50 AM, Sean Christopherson wrote:
> 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?

Sure. MSR_PERF_METRICS actually reports the perf topdown metrics 
portion. I would add more details.


>
>> 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
>>