KVM: Don't WARN if updating IRQ bypass route fails

Don't bother WARNing if updating an IRTE route fails now that vendor code
provides much more precise WARNs.  The generic WARN doesn't provide enough
information to actually debug the problem, and has obviously done nothing
to surface the myriad bugs in KVM x86's implementation.

Drop all of the associated return code plumbing that existed just so that
common KVM could WARN.

Link: https://lore.kernel.org/r/20250611224604.313496-34-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/arm64/kvm/arm.c

@@ -2771,9 +2771,9 @@ bool kvm_arch_irqfd_route_changed(struct kvm_kernel_irq_routing_entry *old,
 	return memcmp(&old->msi, &new->msi, sizeof(new->msi));
 }
 
-int kvm_arch_update_irqfd_routing(struct kvm_kernel_irqfd *irqfd,
-				  struct kvm_kernel_irq_routing_entry *old,
-				  struct kvm_kernel_irq_routing_entry *new)
+void kvm_arch_update_irqfd_routing(struct kvm_kernel_irqfd *irqfd,
+				   struct kvm_kernel_irq_routing_entry *old,
+				   struct kvm_kernel_irq_routing_entry *new)
 {
 	/*
 	 * Remapping the vLPI requires taking the its_lock mutex to resolve

arch/arm64/kvm/vgic/vgic-v4.c

@@ -527,18 +527,17 @@ static struct vgic_irq *__vgic_host_irq_get_vlpi(struct kvm *kvm, int host_irq)
 	return NULL;
 }
 
-int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int host_irq)
+void kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int host_irq)
 {
 	struct vgic_irq *irq;
 	unsigned long flags;
-	int ret = 0;
 
 	if (!vgic_supports_direct_msis(kvm))
-		return 0;
+		return;
 
 	irq = __vgic_host_irq_get_vlpi(kvm, host_irq);
 	if (!irq)
-		return 0;
+		return;
 
 	raw_spin_lock_irqsave(&irq->irq_lock, flags);
 	WARN_ON(irq->hw && irq->host_irq != host_irq);
@@ -550,5 +549,4 @@ int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int host_irq)
 
 	raw_spin_unlock_irqrestore(&irq->irq_lock, flags);
 	vgic_put_irq(kvm, irq);
-	return 0;
 }

arch/x86/kvm/irq.c

@@ -606,11 +606,11 @@ void kvm_arch_irq_bypass_del_producer(struct irq_bypass_consumer *cons,
 	kvm_arch_end_assignment(irqfd->kvm);
 }
 
-int kvm_arch_update_irqfd_routing(struct kvm_kernel_irqfd *irqfd,
-				  struct kvm_kernel_irq_routing_entry *old,
-				  struct kvm_kernel_irq_routing_entry *new)
+void kvm_arch_update_irqfd_routing(struct kvm_kernel_irqfd *irqfd,
+				   struct kvm_kernel_irq_routing_entry *old,
+				   struct kvm_kernel_irq_routing_entry *new)
 {
-	return kvm_pi_update_irte(irqfd, new);
+	kvm_pi_update_irte(irqfd, new);
 }
 
 bool kvm_arch_irqfd_route_changed(struct kvm_kernel_irq_routing_entry *old,

include/kvm/arm_vgic.h

@@ -434,7 +434,7 @@ struct kvm_kernel_irq_routing_entry;
 int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int irq,
 			       struct kvm_kernel_irq_routing_entry *irq_entry);
 
-int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int host_irq);
+void kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int host_irq);
 
 int vgic_v4_load(struct kvm_vcpu *vcpu);
 void vgic_v4_commit(struct kvm_vcpu *vcpu);

include/linux/kvm_host.h

@@ -2410,9 +2410,9 @@ void kvm_arch_irq_bypass_del_producer(struct irq_bypass_consumer *,
 			   struct irq_bypass_producer *);
 void kvm_arch_irq_bypass_stop(struct irq_bypass_consumer *);
 void kvm_arch_irq_bypass_start(struct irq_bypass_consumer *);
-int kvm_arch_update_irqfd_routing(struct kvm_kernel_irqfd *irqfd,
-				  struct kvm_kernel_irq_routing_entry *old,
-				  struct kvm_kernel_irq_routing_entry *new);
+void kvm_arch_update_irqfd_routing(struct kvm_kernel_irqfd *irqfd,
+				   struct kvm_kernel_irq_routing_entry *old,
+				   struct kvm_kernel_irq_routing_entry *new);
 bool kvm_arch_irqfd_route_changed(struct kvm_kernel_irq_routing_entry *,
 				  struct kvm_kernel_irq_routing_entry *);
 #endif /* CONFIG_HAVE_KVM_IRQ_BYPASS */

virt/kvm/eventfd.c

@@ -285,11 +285,11 @@ void __attribute__((weak)) kvm_arch_irq_bypass_start(
 {
 }
 
-int __weak kvm_arch_update_irqfd_routing(struct kvm_kernel_irqfd *irqfd,
-					 struct kvm_kernel_irq_routing_entry *old,
-					 struct kvm_kernel_irq_routing_entry *new)
+void __weak kvm_arch_update_irqfd_routing(struct kvm_kernel_irqfd *irqfd,
+					  struct kvm_kernel_irq_routing_entry *old,
+					  struct kvm_kernel_irq_routing_entry *new)
 {
-	return 0;
+
 }
 
 bool __attribute__((weak)) kvm_arch_irqfd_route_changed(
@@ -617,11 +617,8 @@ void kvm_irq_routing_update(struct kvm *kvm)
 
 #if IS_ENABLED(CONFIG_HAVE_KVM_IRQ_BYPASS)
 		if (irqfd->producer &&
-		    kvm_arch_irqfd_route_changed(&old, &irqfd->irq_entry)) {
-			int ret = kvm_arch_update_irqfd_routing(irqfd, &old, &irqfd->irq_entry);
-
-			WARN_ON(ret);
-		}
+		    kvm_arch_irqfd_route_changed(&old, &irqfd->irq_entry))
+			kvm_arch_update_irqfd_routing(irqfd, &old, &irqfd->irq_entry);
 #endif
 	}