Messages in this thread | | | Date | Thu, 28 Jul 2022 20:02:53 +0800 | Subject | Re: [PATCH 1/3] KVM: x86: Refresh PMU after writes to MSR_IA32_PERF_CAPABILITIES | From | Like Xu <> |
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On 28/7/2022 7:34 am, Sean Christopherson wrote: > Refresh the PMU if userspace modifies MSR_IA32_PERF_CAPABILITIES. KVM > consumes the vCPU's PERF_CAPABILITIES when enumerating PEBS support, but > relies on CPUID updates to refresh the PMU. I.e. KVM will do the wrong > thing if userspace stuffs PERF_CAPABILITIES _after_ setting guest CPUID.
Unwise userspace should reap its consequences if it does not break KVM or host.
When a guest feature can be defined/controlled by multiple KVM APIs entries, (such as SET_CPUID2, msr_feature, KVM_CAP, module_para), should KVM define the priority of these APIs (e.g. whether they can override each other) ?
Removing this ambiguity ensures consistency in the architecture and behavior of all KVM features. Any further performance optimizations can be based on these finalized values as you do.
> > Opportunistically fix a curly-brace indentation. > > Fixes: c59a1f106f5c ("KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS") > Cc: Like Xu <like.xu.linux@gmail.com> > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/kvm/x86.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 5366f884e9a7..362c538285db 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -3543,9 +3543,9 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > return 1; > > vcpu->arch.perf_capabilities = data; > - > + kvm_pmu_refresh(vcpu);
I had proposed this diff but was met with silence.
> return 0; > - } > + } > case MSR_EFER: > return set_efer(vcpu, msr_info); > case MSR_K7_HWCR:
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