From: Sean Christopherson Date: Fri, 23 Sep 2022 00:13:52 +0000 (+0000) Subject: KVM: x86/pmu: Force reprogramming of all counters on PMU filter change X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=f1c5651fda43e0c62a32456cdc6f254f40457409;p=linux.git KVM: x86/pmu: Force reprogramming of all counters on PMU filter change Force vCPUs to reprogram all counters on a PMU filter change to provide a sane ABI for userspace. Use the existing KVM_REQ_PMU to do the programming, and take advantage of the fact that the reprogram_pmi bitmap fits in a u64 to set all bits in a single atomic update. Note, setting the bitmap and making the request needs to be done _after_ the SRCU synchronization to ensure that vCPUs will reprogram using the new filter. KVM's current "lazy" approach is confusing and non-deterministic. It's confusing because, from a developer perspective, the code is buggy as it makes zero sense to let userspace modify the filter but then not actually enforce the new filter. The lazy approach is non-deterministic because KVM enforces the filter whenever a counter is reprogrammed, not just on guest WRMSRs, i.e. a guest might gain/lose access to an event at random times depending on what is going on in the host. Note, the resulting behavior is still non-determinstic while the filter is in flux. If userspace wants to guarantee deterministic behavior, all vCPUs should be paused during the filter update. Jim Mattson Fixes: 66bb8a065f5a ("KVM: x86: PMU Event Filter") Cc: Aaron Lewis Signed-off-by: Sean Christopherson Message-Id: <20220923001355.3741194-2-seanjc@google.com> Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 9362b9736d877..58a562bb197c8 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -527,7 +527,16 @@ struct kvm_pmu { struct kvm_pmc gp_counters[KVM_INTEL_PMC_MAX_GENERIC]; struct kvm_pmc fixed_counters[KVM_PMC_MAX_FIXED]; struct irq_work irq_work; - DECLARE_BITMAP(reprogram_pmi, X86_PMC_IDX_MAX); + + /* + * Overlay the bitmap with a 64-bit atomic so that all bits can be + * set in a single access, e.g. to reprogram all counters when the PMU + * filter changes. + */ + union { + DECLARE_BITMAP(reprogram_pmi, X86_PMC_IDX_MAX); + atomic64_t __reprogram_pmi; + }; DECLARE_BITMAP(all_valid_pmc_idx, X86_PMC_IDX_MAX); DECLARE_BITMAP(pmc_in_use, X86_PMC_IDX_MAX); diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c index de1fd73697365..bf2c32ea3255e 100644 --- a/arch/x86/kvm/pmu.c +++ b/arch/x86/kvm/pmu.c @@ -577,6 +577,8 @@ EXPORT_SYMBOL_GPL(kvm_pmu_trigger_event); int kvm_vm_ioctl_set_pmu_event_filter(struct kvm *kvm, void __user *argp) { struct kvm_pmu_event_filter tmp, *filter; + struct kvm_vcpu *vcpu; + unsigned long i; size_t size; int r; @@ -613,9 +615,18 @@ int kvm_vm_ioctl_set_pmu_event_filter(struct kvm *kvm, void __user *argp) mutex_lock(&kvm->lock); filter = rcu_replace_pointer(kvm->arch.pmu_event_filter, filter, mutex_is_locked(&kvm->lock)); + synchronize_srcu_expedited(&kvm->srcu); + + BUILD_BUG_ON(sizeof(((struct kvm_pmu *)0)->reprogram_pmi) > + sizeof(((struct kvm_pmu *)0)->__reprogram_pmi)); + + kvm_for_each_vcpu(i, vcpu, kvm) + atomic64_set(&vcpu_to_pmu(vcpu)->__reprogram_pmi, -1ull); + + kvm_make_all_cpus_request(kvm, KVM_REQ_PMU); + mutex_unlock(&kvm->lock); - synchronize_srcu_expedited(&kvm->srcu); r = 0; cleanup: kfree(filter);