kvm: remove an atomic on EOI

TMR is set with IRR but does not need to be
cleared on EOI. So we can save an atomic
operation on EOI by checking whether ioapic
needs a specific vector first.

For consistency, don't clear TMR for handled
vectors either: the spec doesn't say that
it needs to be cleared on EOI.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

3 files changed, 21 insertions, 9 deletions

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 858432287ab62..992b4eaae684d 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -92,6 +92,11 @@ static inline int apic_test_and_clear_vector(int vec, void *bitmap)
 	return test_and_clear_bit(VEC_POS(vec), (bitmap) + REG_POS(vec));
 }
 
+static inline int apic_test_vector(int vec, void *bitmap)
+{
+	return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec));
+}
+
 static inline void apic_set_vector(int vec, void *bitmap)
 {
 	set_bit(VEC_POS(vec), (bitmap) + REG_POS(vec));
@@ -480,7 +485,6 @@ int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2)
 static void apic_set_eoi(struct kvm_lapic *apic)
 {
 	int vector = apic_find_highest_isr(apic);
-	int trigger_mode;
 	/*
 	 * Not every write EOI will has corresponding ISR,
 	 * one example is when Kernel check timer on setup_IO_APIC
@@ -491,12 +495,15 @@ static void apic_set_eoi(struct kvm_lapic *apic)
 	apic_clear_vector(vector, apic->regs + APIC_ISR);
 	apic_update_ppr(apic);
 
-	if (apic_test_and_clear_vector(vector, apic->regs + APIC_TMR))
-		trigger_mode = IOAPIC_LEVEL_TRIG;
-	else
-		trigger_mode = IOAPIC_EDGE_TRIG;
-	if (!(apic_get_reg(apic, APIC_SPIV) & APIC_SPIV_DIRECTED_EOI))
+	if (!(apic_get_reg(apic, APIC_SPIV) & APIC_SPIV_DIRECTED_EOI) &&
+	    kvm_ioapic_handles_vector(apic->vcpu->kvm, vector)) {
+		int trigger_mode;
+		if (apic_test_vector(vector, apic->regs + APIC_TMR))
+			trigger_mode = IOAPIC_LEVEL_TRIG;
+		else
+			trigger_mode = IOAPIC_EDGE_TRIG;
 		kvm_ioapic_update_eoi(apic->vcpu->kvm, vector, trigger_mode);
+	}
 	kvm_make_request(KVM_REQ_EVENT, apic->vcpu);
 }
 
diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index dcaf272c26c0e..26fd54dc459ec 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -254,13 +254,17 @@ static void __kvm_ioapic_update_eoi(struct kvm_ioapic *ioapic, int vector,
 	}
 }
 
+bool kvm_ioapic_handles_vector(struct kvm *kvm, int vector)
+{
+	struct kvm_ioapic *ioapic = kvm->arch.vioapic;
+	smp_rmb();
+	return test_bit(vector, ioapic->handled_vectors);
+}
+
 void kvm_ioapic_update_eoi(struct kvm *kvm, int vector, int trigger_mode)
 {
 	struct kvm_ioapic *ioapic = kvm->arch.vioapic;
 
-	smp_rmb();
-	if (!test_bit(vector, ioapic->handled_vectors))
-		return;
 	spin_lock(&ioapic->lock);
 	__kvm_ioapic_update_eoi(ioapic, vector, trigger_mode);
 	spin_unlock(&ioapic->lock);
diff --git a/virt/kvm/ioapic.h b/virt/kvm/ioapic.h
index 0b190c34ccc31..32872a09b63f3 100644
--- a/virt/kvm/ioapic.h
+++ b/virt/kvm/ioapic.h
@@ -71,6 +71,7 @@ int kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
 		int short_hand, int dest, int dest_mode);
 int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2);
 void kvm_ioapic_update_eoi(struct kvm *kvm, int vector, int trigger_mode);
+bool kvm_ioapic_handles_vector(struct kvm *kvm, int vector);
 int kvm_ioapic_init(struct kvm *kvm);
 void kvm_ioapic_destroy(struct kvm *kvm);
 int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int level);