KVM: x86: do not scan IRR twice on APICv vmentry

Calls to apic_find_highest_irr are scanning IRR twice, once
in vmx_sync_pir_from_irr and once in apic_search_irr.  Change
sync_pir_from_irr to get the new maximum IRR from kvm_apic_update_irr;
now that it does the computation, it can also do the RVI write.

In order to avoid complications in svm.c, make the callback optional.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 8af6db9..7ed2400 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -515,6 +515,7 @@ int kvm_lapic_find_highest_irr(struct kvm_vcpu *vcpu)
 	 */
 	return apic_find_highest_irr(vcpu->arch.apic);
 }
+EXPORT_SYMBOL_GPL(kvm_lapic_find_highest_irr);
 
 static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
 			     int vector, int level, int trig_mode,
@@ -580,9 +581,10 @@ static void pv_eoi_clr_pending(struct kvm_vcpu *vcpu)
 static int apic_has_interrupt_for_ppr(struct kvm_lapic *apic, u32 ppr)
 {
 	int highest_irr;
-	if (apic->vcpu->arch.apicv_active)
-		kvm_x86_ops->sync_pir_to_irr(apic->vcpu);
-	highest_irr = apic_find_highest_irr(apic);
+	if (kvm_x86_ops->sync_pir_to_irr && apic->vcpu->arch.apicv_active)
+		highest_irr = kvm_x86_ops->sync_pir_to_irr(apic->vcpu);
+	else
+		highest_irr = apic_find_highest_irr(apic);
 	if (highest_irr == -1 || (highest_irr & 0xF0) <= ppr)
 		return -1;
 	return highest_irr;