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KVM: x86/pmu: WARN and bug the VM if PMU is refreshed after vCPU has run

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Now that KVM disallows changing feature MSRs, i.e. PERF_CAPABILITIES,
after running a vCPU, WARN and bug the VM if the PMU is refreshed after
the vCPU has run.

Note, KVM has disallowed CPUID updates after running a vCPU since commit
feb627e8d6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN"), i.e.
PERF_CAPABILITIES was the only remaining way to trigger a PMU refresh
after KVM_RUN.

Cc: Like Xu <like.xu.linux@gmail.com>
Link: https://lore.kernel.org/r/20230311004618.920745-8-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2023-03-10 16:46:04 -08:00
parent 0094f62c7e
commit 3a6de51a43
2 changed files with 12 additions and 1 deletions
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3
arch/x86/kvm/pmu.c
View File

@ -589,6 +589,9 @@ int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
*/ */
void kvm_pmu_refresh(struct kvm_vcpu *vcpu) void kvm_pmu_refresh(struct kvm_vcpu *vcpu)
{ {
if (KVM_BUG_ON(kvm_vcpu_has_run(vcpu), vcpu->kvm))
return;
bitmap_zero(vcpu_to_pmu(vcpu)->all_valid_pmc_idx, X86_PMC_IDX_MAX); bitmap_zero(vcpu_to_pmu(vcpu)->all_valid_pmc_idx, X86_PMC_IDX_MAX);
static_call(kvm_x86_pmu_refresh)(vcpu); static_call(kvm_x86_pmu_refresh)(vcpu);
} }

10
arch/x86/kvm/x86.c
View File

@ -3632,9 +3632,17 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
if (data & ~kvm_caps.supported_perf_cap) if (data & ~kvm_caps.supported_perf_cap)
return 1; return 1;
/*
* Note, this is not just a performance optimization! KVM
* disallows changing feature MSRs after the vCPU has run; PMU
* refresh will bug the VM if called after the vCPU has run.
*/
if (vcpu->arch.perf_capabilities == data)
break;
vcpu->arch.perf_capabilities = data; vcpu->arch.perf_capabilities = data;
kvm_pmu_refresh(vcpu); kvm_pmu_refresh(vcpu);
return 0; break;
case MSR_EFER: case MSR_EFER:
return set_efer(vcpu, msr_info); return set_efer(vcpu, msr_info);
case MSR_K7_HWCR: case MSR_K7_HWCR: