Re: [PATCH v5 15/44] KVM: SVM: Check pmu->version, not enable_pmu, when getting PMC MSRs

Sandipan Das
2025-08-13T09:59:07Z

On 07-08-2025 01:26, Sean Christopherson wrote:
> Gate access to PMC MSRs based on pmu->version, not on kvm->arch.enable_pmu,
> to more accurately reflect KVM's behavior. This is a glorified nop, as
> pmu->version and pmu->nr_arch_gp_counters can only be non-zero if
> amd_pmu_refresh() is reached, kvm_pmu_refresh() invokes amd_pmu_refresh()
> if and only if kvm->arch.enable_pmu is true, and amd_pmu_refresh() forces
> pmu->version to be 1 or 2.
>
> I.e. the following holds true:
>
> !pmu->nr_arch_gp_counters || kvm->arch.enable_pmu == (pmu->version > 0)
>
> and so the only way for amd_pmu_get_pmc() to return a non-NULL value is if
> both kvm->arch.enable_pmu and pmu->version evaluate to true.
>
> No real functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/svm/pmu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
> index 288f7f2a46f2..7b8577f3c57a 100644
> --- a/arch/x86/kvm/svm/pmu.c
> +++ b/arch/x86/kvm/svm/pmu.c
> @@ -41,7 +41,7 @@ static inline struct kvm_pmc *get_gp_pmc_amd(struct kvm_pmu *pmu, u32 msr,
> struct kvm_vcpu *vcpu = pmu_to_vcpu(pmu);
> unsigned int idx;
>
> - if (!vcpu->kvm->arch.enable_pmu)
> + if (!pmu->version)
> return NULL;
>
> switch (msr) {

Reviewed-by: Sandipan Das <sandipan.das@amd.com>