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Commit 2e4682ba authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Radim Krčmář
Browse files

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: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 46971a2f

arch/x86/kvm/irq_comm.c

+0 −3
Original line number Diff line number Diff line
@@ -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,

include/linux/kvm_host.h

+11 −0
Original line number Diff line number Diff line
@@ -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;