On 11/21/2024 12:45 AM, Sean Christopherson wrote: > On Wed, Nov 20, 2024, Dapeng Mi wrote: >> On 11/19/2024 10:54 PM, Sean Christopherson wrote: >>> On Thu, Aug 01, 2024, Mingwei Zhang wrote: >>>> Plumb through pass-through PMU setting from kvm->arch into kvm_pmu on each >>>> vcpu created. Note that enabling PMU is decided by VMM when it sets the >>>> CPUID bits exposed to guest VM. So plumb through the enabling for each pmu >>>> in intel_pmu_refresh(). >>> Why? As with the per-VM snapshot, I see zero reason for this to exist, it's >>> simply: >>> >>> kvm->arch.enable_pmu && enable_mediated_pmu && pmu->version; >>> >>> And in literally every correct usage of pmu->passthrough, kvm->arch.enable_pmu >>> and pmu->version have been checked (though implicitly), i.e. KVM can check >>> enable_mediated_pmu and nothing else. >> Ok, too many passthrough_pmu flags indeed confuse readers. Besides these >> dependencies, mediated vPMU also depends on lapic_in_kernel(). We need to >> set enable_mediated_pmu to false as well if lapic_in_kernel() returns false. > No, just kill the entire vPMU. > > Also, the need for an in-kernel APIC isn't unique to the mediated PMU. KVM simply > drops PMIs if there's no APIC. > > If we're feeling lucky, we could try a breaking change like so: > > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c > index fcd188cc389a..bb08155f6198 100644 > --- a/arch/x86/kvm/pmu.c > +++ b/arch/x86/kvm/pmu.c > @@ -817,7 +817,7 @@ void kvm_pmu_refresh(struct kvm_vcpu *vcpu) > pmu->pebs_data_cfg_mask = ~0ull; > bitmap_zero(pmu->all_valid_pmc_idx, X86_PMC_IDX_MAX); > > - if (!vcpu->kvm->arch.enable_pmu) > + if (!vcpu->kvm->arch.enable_pmu || !lapic_in_kernel(vcpu)) > return; > > static_call(kvm_x86_pmu_refresh)(vcpu); > > > If we don't want to risk breaking weird setups, we could restrict the behavior > to the mediated PMU being enabled: > > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c > index fcd188cc389a..bc9673190574 100644 > --- a/arch/x86/kvm/pmu.c > +++ b/arch/x86/kvm/pmu.c > @@ -817,7 +817,8 @@ void kvm_pmu_refresh(struct kvm_vcpu *vcpu) > pmu->pebs_data_cfg_mask = ~0ull; > bitmap_zero(pmu->all_valid_pmc_idx, X86_PMC_IDX_MAX); > > - if (!vcpu->kvm->arch.enable_pmu) > + if (!vcpu->kvm->arch.enable_pmu || > + (!lapic_in_kernel(vcpu) && enable_mediated_pmu)) > return; > > static_call(kvm_x86_pmu_refresh)(vcpu); Sure. would adopt the latter one for safe. :)
