2024-01-26 10:00:34

by Zhang, Xiong Y

Subject: [RFC PATCH 27/41] KVM: x86/pmu: Clear PERF_METRICS MSR for guest

From: Dapeng Mi <[email protected]>

Since perf topdown metrics feature is not supported yet, clear
PERF_METRICS MSR for guest.

Signed-off-by: Dapeng Mi <[email protected]>
---
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

2024-04-11 21:50:39

by Sean Christopherson

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 <[email protected]>
>
> 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 <[email protected]>
> ---
> 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
>

2024-04-13 08:16:46

by Mi, Dapeng

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 <[email protected]>
>>
>> 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 <[email protected]>
>> ---
>> 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
>>