KVM: add missing memory barrier in kvm_{make,check}_request
kvm_make_request and kvm_check_request imply a producer-consumer
relationship; add implicit memory barriers to them. There was indeed
already a place that was adding an explicit smp_mb() to order between
kvm_check_request and the processing of the request. That memory
barrier can be removed (as an added benefit, kvm_check_request can use
smp_mb__after_atomic which is free on x86).
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 5276fe0..ad40d44 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1091,6 +1091,11 @@
static inline void kvm_make_request(int req, struct kvm_vcpu *vcpu)
{
+ /*
+ * Ensure the rest of the request is published to kvm_check_request's
+ * caller. Paired with the smp_mb__after_atomic in kvm_check_request.
+ */
+ smp_wmb();
set_bit(req, &vcpu->requests);
}
@@ -1098,6 +1103,12 @@
{
if (test_bit(req, &vcpu->requests)) {
clear_bit(req, &vcpu->requests);
+
+ /*
+ * Ensure the rest of the request is visible to kvm_check_request's
+ * caller. Paired with the smp_wmb in kvm_make_request.
+ */
+ smp_mb__after_atomic();
return true;
} else {
return false;