KVM: arm64: vgic-v4: Only attempt vLPI mapping for actual MSIs

Some 'creative' VMMs out there may assign a VFIO MSI eventfd to an SPI
routing entry.

And yes, I can already hear you shouting about possibly driving a level
interrupt with an edge-sensitive one. You know who you are.

This works for the most part, and interrupt injection winds up taking
the software path. However, when running on GICv4-enabled hardware, KVM
erroneously attempts to setup LPI forwarding, even though the KVM
routing isn't an MSI.

Thanks to misuse of a union, the MSI destination is unlikely to match any
ITS in the VM and kvm_vgic_v4_set_forwarding() bails early. Later on when
the VM is being torn down, this half-configured state triggers the
WARN_ON() in kvm_vgic_v4_unset_forwarding() due to the fact that no HW
IRQ was ever assigned.

Avoid the whole mess by preventing SPI routing entries from getting into
the LPI forwarding helpers.

Reported-by: Sudheer Dantuluri <dantuluris@google.com>
Tested-by: Sudheer Dantuluri <dantuluris@google.com>
Fixes: 196b136 ("KVM: arm/arm64: GICv4: Wire mapping/unmapping of VLPIs in VFIO irq bypass")
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250226183124.82094-2-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: oupton

arch/arm64/kvm/arm.c

@@ -2717,6 +2717,14 @@ int kvm_arch_irq_bypass_add_producer(struct irq_bypass_consumer *cons,
 {
 	struct kvm_kernel_irqfd *irqfd =
 		container_of(cons, struct kvm_kernel_irqfd, consumer);
+	struct kvm_kernel_irq_routing_entry *irq_entry = &irqfd->irq_entry;
+
+	/*
+	 * The only thing we have a chance of directly-injecting is LPIs. Maybe
+	 * one day...
+	 */
+	if (irq_entry->type != KVM_IRQ_ROUTING_MSI)
+		return 0;
 
 	return kvm_vgic_v4_set_forwarding(irqfd->kvm, prod->irq,
 					  &irqfd->irq_entry);
@@ -2726,6 +2734,10 @@ void kvm_arch_irq_bypass_del_producer(struct irq_bypass_consumer *cons,
 {
 	struct kvm_kernel_irqfd *irqfd =
 		container_of(cons, struct kvm_kernel_irqfd, consumer);
+	struct kvm_kernel_irq_routing_entry *irq_entry = &irqfd->irq_entry;
+
+	if (irq_entry->type != KVM_IRQ_ROUTING_MSI)
+		return;
 
 	kvm_vgic_v4_unset_forwarding(irqfd->kvm, prod->irq,
 				     &irqfd->irq_entry);