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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>
This commit is contained in:
Paolo Bonzini 2016-03-10 16:30:22 +01:00 committed by Radim Krčmář
parent 46971a2f59
commit 2e4682ba2e
2 changed files with 11 additions and 3 deletions
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3
arch/x86/kvm/irq_comm.c
View File

@ -382,9 +382,6 @@ void kvm_scan_ioapic_routes(struct kvm_vcpu *vcpu,
u32 i, nr_ioapic_pins;
int idx;
/* kvm->irq_routing must be read after clearing
* KVM_SCAN_IOAPIC. */
smp_mb();
idx = srcu_read_lock(&kvm->irq_srcu);
table = srcu_dereference(kvm->irq_routing, &kvm->irq_srcu);
nr_ioapic_pins = min_t(u32, table->nr_rt_entries,

11
include/linux/kvm_host.h
View File

@ -1091,6 +1091,11 @@ static inline bool kvm_vcpu_compatible(struct kvm_vcpu *vcpu) { return true; }
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 @@ static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
{
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;