2023-04-04 07:22:39

by Like Xu

Subject: [PATCH] KVM: x86/pmu: Zero out pmu->all_valid_pmc_idx each time it's refreshed

From: Like Xu <[email protected]>

The kvm_pmu_refresh() may be called repeatedly (e.g. configure guest
CPUID repeatedly or update MSR_IA32_PERF_CAPABILITIES) and each
call will use the last pmu->all_valid_pmc_idx value, with the residual
bits introducing additional overhead later in the vPMU emulation.

Fixes: b35e5548b411 ("KVM: x86/vPMU: Add lazy mechanism to release perf_event per vPMC")
Suggested-by: Sean Christopherson <[email protected]>
Signed-off-by: Like Xu <[email protected]>
---
arch/x86/kvm/pmu.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 612e6c70ce2e..29492c2a0c82 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -589,6 +589,7 @@ int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
*/
void kvm_pmu_refresh(struct kvm_vcpu *vcpu)
{
+ bitmap_zero(vcpu_to_pmu(vcpu)->all_valid_pmc_idx, X86_PMC_IDX_MAX);
static_call(kvm_x86_pmu_refresh)(vcpu);
}

--
2.40.0

2023-04-06 00:02:40

by Sean Christopherson

Subject: Re: [PATCH] KVM: x86/pmu: Zero out pmu->all_valid_pmc_idx each time it's refreshed

On Tue, 04 Apr 2023 15:17:59 +0800, Like Xu wrote:
> The kvm_pmu_refresh() may be called repeatedly (e.g. configure guest
> CPUID repeatedly or update MSR_IA32_PERF_CAPABILITIES) and each
> call will use the last pmu->all_valid_pmc_idx value, with the residual
> bits introducing additional overhead later in the vPMU emulation.
>
>

Applied to kvm-x86 pmu, thanks!

[1/1] KVM: x86/pmu: Zero out pmu->all_valid_pmc_idx each time it's refreshed
https://github.com/kvm-x86/linux/commit/7e768ce8278b

--
https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes