KVM: inject ExtINT interrupt before APIC interrupts

According to Intel SDM Volume 3 Section 10.8.1 "Interrupt Handling with
the Pentium 4 and Intel Xeon Processors" and Section 10.8.2 "Interrupt
Handling with the P6 Family and Pentium Processors" ExtINT interrupts are
sent directly to the processor core for handling. Currently KVM checks
APIC before it considers ExtINT interrupts for injection which is
backwards from the spec. Make code behave according to the SDM.
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Acked-by: "Zhang, Yang Z" <yang.z.zhang@intel.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/i8259.c

@@ -241,6 +241,8 @@ int kvm_pic_read_irq(struct kvm *kvm)
 	int irq, irq2, intno;
 	struct kvm_pic *s = pic_irqchip(kvm);
 
+	s->output = 0;
+
 	pic_lock(s);
 	irq = pic_get_irq(&s->pics[0]);
 	if (irq >= 0) {

arch/x86/kvm/irq.c

@@ -48,14 +48,10 @@ int kvm_cpu_has_interrupt(struct kvm_vcpu *v)
 	if (!irqchip_in_kernel(v->kvm))
 		return v->arch.interrupt.pending;
 
-	if (kvm_apic_has_interrupt(v) == -1) {	/* LAPIC */
-		if (kvm_apic_accept_pic_intr(v)) {
-			s = pic_irqchip(v->kvm);	/* PIC */
-			return s->output;
-		} else
-			return 0;
-	}
-	return 1;
+	if (kvm_apic_accept_pic_intr(v) && pic_irqchip(v->kvm)->output)
+		return pic_irqchip(v->kvm)->output;	/* PIC */
+
+	return kvm_apic_has_interrupt(v) != -1;	/* LAPIC */
 }
 EXPORT_SYMBOL_GPL(kvm_cpu_has_interrupt);
 
@@ -65,20 +61,14 @@ EXPORT_SYMBOL_GPL(kvm_cpu_has_interrupt);
 int kvm_cpu_get_interrupt(struct kvm_vcpu *v)
 {
 	struct kvm_pic *s;
-	int vector;
 
 	if (!irqchip_in_kernel(v->kvm))
 		return v->arch.interrupt.nr;
 
-	vector = kvm_get_apic_interrupt(v);	/* APIC */
-	if (vector == -1) {
-		if (kvm_apic_accept_pic_intr(v)) {
-			s = pic_irqchip(v->kvm);
-			s->output = 0;		/* PIC */
-			vector = kvm_pic_read_irq(v->kvm);
-		}
-	}
-	return vector;
+	if (kvm_apic_accept_pic_intr(v) && pic_irqchip(v->kvm)->output)
+		return kvm_pic_read_irq(v->kvm);	/* PIC */
+
+	return kvm_get_apic_interrupt(v);	/* APIC */
 }
 EXPORT_SYMBOL_GPL(kvm_cpu_get_interrupt);