2021-10-08 10:00:11

by Wanpeng Li

Subject: [PATCH 2/3] KVM: vPMU: Fill get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0

From: Wanpeng Li <[email protected]>

SDM section 18.2.3 mentioned that:

"IA32_PERF_GLOBAL_OVF_CTL MSR allows software to clear overflow indicator(s) of
any general-purpose or fixed-function counters via a single WRMSR."

It is R/W mentioned by SDM, we read this msr on bare-metal during perf testing,
the value is always 0 for CLX/SKX boxes on hands. Let's fill get_msr
MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0 as hardware behavior.

Signed-off-by: Wanpeng Li <[email protected]>
---
Btw, xen also fills get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL 0.

arch/x86/kvm/vmx/pmu_intel.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 10cc4f65c4ef..47260a8563f9 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -365,7 +365,7 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
msr_info->data = pmu->global_ctrl;
return 0;
case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
- msr_info->data = pmu->global_ovf_ctrl;
+ msr_info->data = 0;
return 0;
default:
if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
--
2.25.1

2021-10-08 11:04:36

by Like Xu

Subject: Re: [PATCH 2/3] KVM: vPMU: Fill get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0

cc Andi,

On 8/10/2021 5:57 pm, Wanpeng Li wrote:
> From: Wanpeng Li <[email protected]>
>
> SDM section 18.2.3 mentioned that:
>
> "IA32_PERF_GLOBAL_OVF_CTL MSR allows software to clear overflow indicator(s) of
> any general-purpose or fixed-function counters via a single WRMSR."
>
> It is R/W mentioned by SDM, we read this msr on bare-metal during perf testing,
> the value is always 0 for CLX/SKX boxes on hands. Let's fill get_msr
> MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0 as hardware behavior.
>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> Btw, xen also fills get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL 0.
>
> arch/x86/kvm/vmx/pmu_intel.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 10cc4f65c4ef..47260a8563f9 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -365,7 +365,7 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> msr_info->data = pmu->global_ctrl;
> return 0;
> case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
> - msr_info->data = pmu->global_ovf_ctrl;
> + msr_info->data = 0;

Tested-by: Like Xu <[email protected]>

Further, better to drop 'u64 global_ovf_ctrl' directly.

> return 0;
> default:
> if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
>

2021-10-08 11:20:27

by Wanpeng Li

Subject: Re: [PATCH 2/3] KVM: vPMU: Fill get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0

On Fri, 8 Oct 2021 at 19:02, Like Xu <[email protected]> wrote:
>
> cc Andi,
>
> On 8/10/2021 5:57 pm, Wanpeng Li wrote:
> > From: Wanpeng Li <[email protected]>
> >
> > SDM section 18.2.3 mentioned that:
> >
> > "IA32_PERF_GLOBAL_OVF_CTL MSR allows software to clear overflow indicator(s) of
> > any general-purpose or fixed-function counters via a single WRMSR."
> >
> > It is R/W mentioned by SDM, we read this msr on bare-metal during perf testing,
> > the value is always 0 for CLX/SKX boxes on hands. Let's fill get_msr
> > MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0 as hardware behavior.
> >
> > Signed-off-by: Wanpeng Li <[email protected]>
> > ---
> > Btw, xen also fills get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL 0.
> >
> > arch/x86/kvm/vmx/pmu_intel.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> > index 10cc4f65c4ef..47260a8563f9 100644
> > --- a/arch/x86/kvm/vmx/pmu_intel.c
> > +++ b/arch/x86/kvm/vmx/pmu_intel.c
> > @@ -365,7 +365,7 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> > msr_info->data = pmu->global_ctrl;
> > return 0;
> > case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
> > - msr_info->data = pmu->global_ovf_ctrl;
> > + msr_info->data = 0;
>
> Tested-by: Like Xu <[email protected]>

Thanks.

> Further, better to drop 'u64 global_ovf_ctrl' directly.

Good suggestion. :)

Wanpeng