Commit 95744a90 authored by Michal Luczaj's avatar Michal Luczaj Committed by Sean Christopherson
Browse files

KVM: x86: Optimize kvm->lock and SRCU interaction (KVM_SET_PMU_EVENT_FILTER) 



Reduce time spent holding kvm->lock: unlock mutex before calling
synchronize_srcu_expedited().  There is no need to hold kvm->lock until
all vCPUs have been kicked, KVM only needs to guarantee that all vCPUs
will switch to the new filter before exiting to userspace.  Protecting
the write to __reprogram_pmi is also unnecessary as a vCPU may process
a set bit before receiving the final KVM_REQ_PMU, but the per-vCPU writes
are guaranteed to occur after all vCPUs have switched to the new filter.

Suggested-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Suggested-by: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarMichal Luczaj <mhal@rbox.co>
Link: https://lore.kernel.org/r/20230107001256.2365304-2-mhal@rbox.co


[sean: expand changelog]
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 096691e0

arch/x86/kvm/pmu.c

+1 −2
Original line number Diff line number Diff line
@@ -634,6 +634,7 @@ 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));

	mutex_unlock(&kvm->lock);

	synchronize_srcu_expedited(&kvm->srcu);



	BUILD_BUG_ON(sizeof(((struct kvm_pmu *)0)->reprogram_pmi) >
@@ -644,8 +645,6 @@ int kvm_vm_ioctl_set_pmu_event_filter(struct kvm *kvm, void __user *argp) 


	kvm_make_all_cpus_request(kvm, KVM_REQ_PMU);



	mutex_unlock(&kvm->lock);



	r = 0;

cleanup:

	kfree(filter);