diff options
| author | Paolo Bonzini | 2021-10-20 06:38:05 -0400 |
|---|---|---|
| committer | Paolo Bonzini | 2021-12-08 04:24:44 -0500 |
| commit | aefdc2ed445eb470bdba108bd6a19fb232d3bada (patch) | |
| tree | e43dae70e1e18b3d19304fe2c8c88959f16d22d9 | |
| parent | fb43496c8362b8b379b4348b581f8f88f47cd1f8 (diff) | |
KVM: Avoid atomic operations when kicking the running vCPU
If we do have the vcpu mutex, as is the case if kvm_running_vcpu is set
to the target vcpu of the kick, changes to vcpu->mode do not need atomic
operations; cmpxchg is only needed _outside_ the mutex to ensure that
the IN_GUEST_MODE->EXITING_GUEST_MODE change does not race with the vcpu
thread going OUTSIDE_GUEST_MODE.
Use this to optimize the case of a vCPU sending an interrupt to itself.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
| -rw-r--r-- | virt/kvm/kvm_main.c | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index f93b60165fd7..e9990c4c6e40 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3396,6 +3396,19 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu) if (kvm_vcpu_wake_up(vcpu)) return; + me = get_cpu(); + /* + * The only state change done outside the vcpu mutex is IN_GUEST_MODE + * to EXITING_GUEST_MODE. Therefore the moderately expensive "should + * kick" check does not need atomic operations if kvm_vcpu_kick is used + * within the vCPU thread itself. + */ + if (vcpu == __this_cpu_read(kvm_running_vcpu)) { + if (vcpu->mode == IN_GUEST_MODE) + WRITE_ONCE(vcpu->mode, EXITING_GUEST_MODE); + goto out; + } + /* * Note, the vCPU could get migrated to a different pCPU at any point * after kvm_arch_vcpu_should_kick(), which could result in sending an @@ -3403,12 +3416,12 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu) * IPI is to force the vCPU to leave IN_GUEST_MODE, and migrating the * vCPU also requires it to leave IN_GUEST_MODE. */ - me = get_cpu(); if (kvm_arch_vcpu_should_kick(vcpu)) { cpu = READ_ONCE(vcpu->cpu); if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) smp_send_reschedule(cpu); } +out: put_cpu(); } EXPORT_SYMBOL_GPL(kvm_vcpu_kick); |