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Peter Anvin" , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, Yongwei Ma , Xiong Zhang , Dapeng Mi , Jim Mattson , Zide Chen , Eranian Stephane , Shukla Manali , Nikunj Dadhania Content-Type: text/plain; charset="us-ascii" On Mon, May 26, 2025, Sandipan Das wrote: > > @@ -212,6 +212,18 @@ static void amd_pmu_refresh(struct kvm_vcpu *vcpu) > > bitmap_set(pmu->all_valid_pmc_idx, 0, pmu->nr_arch_gp_counters); > > } > > > > +static void amd_pmu_refresh(struct kvm_vcpu *vcpu) > > +{ > > + struct vcpu_svm *svm = to_svm(vcpu); > > + > > + __amd_pmu_refresh(vcpu); > > + > > + if (kvm_rdpmc_in_guest(vcpu)) > > + svm_clr_intercept(svm, INTERCEPT_RDPMC); > > + else > > + svm_set_intercept(svm, INTERCEPT_RDPMC); > > +} > > + > > After putting kprobes on kvm_pmu_rdpmc(), I noticed that RDPMC instructions were > getting intercepted for the secondary vCPUs. This happens because when secondary > vCPUs come up, kvm_vcpu_reset() gets called after guest CPUID has been updated. > While RDPMC interception is initially disabled in the kvm_pmu_refresh() path, it > gets re-enabled in the kvm_vcpu_reset() path as svm_vcpu_reset() calls init_vmcb(). > We should consider adding the following change to avoid that. Revisiting this code after the MSR interception rework, I think we should go for a more complete, big-hammer solution. Rather than manipulate intercepts during kvm_pmu_refresh(), do the updates as part of the "common" recalc intercepts flow. And then to trigger recalc on PERF_CAPABILITIES writes, turn KVM_REQ_MSR_FILTER_CHANGED into a generic KVM_REQ_RECALC_INTERCEPTS. That way there's one path for calculating dynamic intercepts, which should make it much more difficult for us to screw up things like reacting to MSR filter changes. And providing a single path avoids needing to have a series of back-and-forth calls between common x86 code, PMU code, and vendor code.