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: 196b136498b3 ("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>

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index b8e55a441282f57cb2d4bc55a43b41d5b774dfdd..36d8dd80b4310f2db159255d0556c4ff8d4b9d1b 100644 (file)
--- a/arch/arm64/kvm/arm.c
+++ b/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);