iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

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

Browse Source 
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: Paolo Bonzini <pbonzini@redhat.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://lore.kernel.org/r/20230107001256.2365304-2-mhal@rbox.co
[sean: expand changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Michal Luczaj 2023-01-07 01:12:51 +01:00 committed by Sean Christopherson
parent 096691e0d2
commit 95744a90db
1 changed files with 1 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/x86/kvm/pmu.c
View File

@ -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);