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>

arch/x86/include/asm/kvm_host.h

@@ -969,7 +969,7 @@ struct kvm_x86_ops {
 	void (*set_virtual_x2apic_mode)(struct kvm_vcpu *vcpu, bool set);
 	void (*set_apic_access_page_addr)(struct kvm_vcpu *vcpu, hpa_t hpa);
 	void (*deliver_posted_interrupt)(struct kvm_vcpu *vcpu, int vector);
-	void (*sync_pir_to_irr)(struct kvm_vcpu *vcpu);
+	int (*sync_pir_to_irr)(struct kvm_vcpu *vcpu);
 	int (*set_tss_addr)(struct kvm *kvm, unsigned int addr);
 	int (*get_tdp_level)(void);
 	u64 (*get_mt_mask)(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);

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;

arch/x86/kvm/svm.c

@@ -4359,11 +4359,6 @@ static void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
 	return;
 }
 
-static void svm_sync_pir_to_irr(struct kvm_vcpu *vcpu)
-{
-	return;
-}
-
 static void svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec)
 {
 	kvm_lapic_set_irr(vec, vcpu->arch.apic);
@@ -5373,7 +5368,6 @@ static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
 	.get_enable_apicv = svm_get_enable_apicv,
 	.refresh_apicv_exec_ctrl = svm_refresh_apicv_exec_ctrl,
 	.load_eoi_exitmap = svm_load_eoi_exitmap,
-	.sync_pir_to_irr = svm_sync_pir_to_irr,
 	.hwapic_irr_update = svm_hwapic_irr_update,
 	.hwapic_isr_update = svm_hwapic_isr_update,
 	.apicv_post_state_restore = avic_post_state_restore,

arch/x86/kvm/vmx.c

@@ -6649,8 +6649,10 @@ static __init int hardware_setup(void)
 	if (!cpu_has_vmx_ple())
 		ple_gap = 0;
 
-	if (!cpu_has_vmx_apicv())
+	if (!cpu_has_vmx_apicv()) {
 		enable_apicv = 0;
+		kvm_x86_ops->sync_pir_to_irr = NULL;
+	}
 
 	if (cpu_has_vmx_tsc_scaling()) {
 		kvm_has_tsc_control = true;
@@ -8722,20 +8724,25 @@ static void vmx_hwapic_irr_update(struct kvm_vcpu *vcpu, int max_irr)
 	}
 }
 
-static void vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
+static int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	int max_irr;
 
-	if (!pi_test_on(&vmx->pi_desc))
-		return;
-
-	pi_clear_on(&vmx->pi_desc);
-	/*
-	 * IOMMU can write to PIR.ON, so the barrier matters even on UP.
-	 * But on x86 this is just a compiler barrier anyway.
-	 */
-	smp_mb__after_atomic();
-	kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
+	WARN_ON(!vcpu->arch.apicv_active);
+	if (pi_test_on(&vmx->pi_desc)) {
+		pi_clear_on(&vmx->pi_desc);
+		/*
+		 * IOMMU can write to PIR.ON, so the barrier matters even on UP.
+		 * But on x86 this is just a compiler barrier anyway.
+		 */
+		smp_mb__after_atomic();
+		max_irr = kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
+	} else {
+		max_irr = kvm_lapic_find_highest_irr(vcpu);
+	}
+	vmx_hwapic_irr_update(vcpu, max_irr);
+	return max_irr;
 }
 
 static void vmx_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)

arch/x86/kvm/x86.c

@@ -2909,7 +2909,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu,
 				    struct kvm_lapic_state *s)
 {
-	if (vcpu->arch.apicv_active)
+	if (kvm_x86_ops->sync_pir_to_irr && vcpu->arch.apicv_active)
 		kvm_x86_ops->sync_pir_to_irr(vcpu);
 
 	return kvm_apic_get_state(vcpu, s);
@@ -6659,7 +6659,7 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
 	if (irqchip_split(vcpu->kvm))
 		kvm_scan_ioapic_routes(vcpu, vcpu->arch.ioapic_handled_vectors);
 	else {
-		if (vcpu->arch.apicv_active)
+		if (kvm_x86_ops->sync_pir_to_irr && vcpu->arch.apicv_active)
 			kvm_x86_ops->sync_pir_to_irr(vcpu);
 		kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
 	}
@@ -6822,11 +6822,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		 * Update architecture specific hints for APIC
 		 * virtual interrupt delivery.
 		 */
-		if (vcpu->arch.apicv_active) {
+		if (kvm_x86_ops->sync_pir_to_irr && vcpu->arch.apicv_active)
 			kvm_x86_ops->sync_pir_to_irr(vcpu);
-			kvm_x86_ops->hwapic_irr_update(vcpu,
-				kvm_lapic_find_highest_irr(vcpu));
-		}
 	}
 
 	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {