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Message-ID: <64c895af-67a2-48de-b509-dd44d295ffe9@linux.intel.com>
Date: Sat, 13 Apr 2024 11:29:55 +0800
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Subject: Re: [RFC PATCH 27/41] KVM: x86/pmu: Clear PERF_METRICS MSR for guest
To: Sean Christopherson <seanjc@google.com>,
 Xiong Zhang <xiong.y.zhang@linux.intel.com>
Cc: pbonzini@redhat.com, peterz@infradead.org, mizhang@google.com,
 kan.liang@intel.com, zhenyuw@linux.intel.com, jmattson@google.com,
 kvm@vger.kernel.org, linux-perf-users@vger.kernel.org,
 linux-kernel@vger.kernel.org, zhiyuan.lv@intel.com, eranian@google.com,
 irogers@google.com, samantha.alt@intel.com, like.xu.linux@gmail.com,
 chao.gao@intel.com
References: <20240126085444.324918-1-xiong.y.zhang@linux.intel.com>
 <20240126085444.324918-28-xiong.y.zhang@linux.intel.com>
 <ZhhbJCGcJ6Rshkfk@google.com>
Content-Language: en-US
From: "Mi, Dapeng" <dapeng1.mi@linux.intel.com>
In-Reply-To: <ZhhbJCGcJ6Rshkfk@google.com>
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On 4/12/2024 5:50 AM, Sean Christopherson wrote:
> On Fri, Jan 26, 2024, Xiong Zhang wrote:
>> From: Dapeng Mi <dapeng1.mi@linux.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@linux.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
>>