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    SubjectRe: [PATCH v11 10/11] KVM: x86/pmu: Check guest LBR availability in case host reclaims them
    On Thu, May 14, 2020 at 04:30:53PM +0800, Like Xu wrote:

    > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
    > index ea4faae56473..db185dca903d 100644
    > --- a/arch/x86/kvm/vmx/pmu_intel.c
    > +++ b/arch/x86/kvm/vmx/pmu_intel.c
    > @@ -646,6 +646,43 @@ static void intel_pmu_lbr_cleanup(struct kvm_vcpu *vcpu)
    > intel_pmu_free_lbr_event(vcpu);
    > }
    >
    > +static bool intel_pmu_lbr_is_availabile(struct kvm_vcpu *vcpu)
    > +{
    > + struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
    > +
    > + if (!pmu->lbr_event)
    > + return false;
    > +
    > + if (event_is_oncpu(pmu->lbr_event)) {
    > + intel_pmu_intercept_lbr_msrs(vcpu, false);
    > + } else {
    > + intel_pmu_intercept_lbr_msrs(vcpu, true);
    > + return false;
    > + }
    > +
    > + return true;
    > +}

    This is unreadable gunk, what?

    > +/*
    > + * Higher priority host perf events (e.g. cpu pinned) could reclaim the
    > + * pmu resources (e.g. LBR) that were assigned to the guest. This is
    > + * usually done via ipi calls (more details in perf_install_in_context).
    > + *
    > + * Before entering the non-root mode (with irq disabled here), double
    > + * confirm that the pmu features enabled to the guest are not reclaimed
    > + * by higher priority host events. Otherwise, disallow vcpu's access to
    > + * the reclaimed features.
    > + */
    > +static void intel_pmu_availability_check(struct kvm_vcpu *vcpu)
    > +{
    > + lockdep_assert_irqs_disabled();
    > +
    > + if (lbr_is_enabled(vcpu) && !intel_pmu_lbr_is_availabile(vcpu) &&
    > + (vmcs_read64(GUEST_IA32_DEBUGCTL) & DEBUGCTLMSR_LBR))
    > + pr_warn_ratelimited("kvm: vcpu-%d: LBR is temporarily unavailable.\n",
    > + vcpu->vcpu_id);

    More unreadable nonsense; when the events go into ERROR state, it's a
    permanent fail, they'll not come back.

    > +}
    > +
    > struct kvm_pmu_ops intel_pmu_ops = {
    > .find_arch_event = intel_find_arch_event,
    > .find_fixed_event = intel_find_fixed_event,
    > @@ -662,4 +699,5 @@ struct kvm_pmu_ops intel_pmu_ops = {
    > .reset = intel_pmu_reset,
    > .deliver_pmi = intel_pmu_deliver_pmi,
    > .lbr_cleanup = intel_pmu_lbr_cleanup,
    > + .availability_check = intel_pmu_availability_check,
    > };
    > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
    > index 9969d663826a..80d036c5f64a 100644
    > --- a/arch/x86/kvm/vmx/vmx.c
    > +++ b/arch/x86/kvm/vmx/vmx.c
    > @@ -6696,8 +6696,10 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
    >
    > pt_guest_enter(vmx);
    >
    > - if (vcpu_to_pmu(vcpu)->version)
    > + if (vcpu_to_pmu(vcpu)->version) {
    > atomic_switch_perf_msrs(vmx);
    > + kvm_x86_ops.pmu_ops->availability_check(vcpu);
    > + }

    AFAICT you just did a call out to the kvm_pmu crud in
    atomic_switch_perf_msrs(), why do another call?


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