KVM: dont clear TMR on EOI

Intel spec says that TMR needs to be set/cleared
when IRR is set, but kvm also clears it on  EOI.

I did some tests on a real (AMD based) system,
and I see same TMR values both before
and after EOI, so I think it's a minor bug in kvm.

This patch fixes TMR to be set/cleared on IRR set
only as per spec.

And now that we don't clear TMR, we can save
an atomic read of TMR on EOI that's not propagated
to ioapic, by checking whether ioapic needs
a specific vector first and calculating
the mode afterwards.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

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);
 }
 

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);

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);