Commit 5c57533e authored by Oliver Upton's avatar Oliver Upton
Browse files

KVM: arm64: vgic-v4: Fall back to software irqbypass if LPI not found 



Continuing with the theme of broken VMMs and guests, irqbypass
registration can fail if the virtual ITS lacks a translation for the
MSI. Either the guest hasn't mapped it or userspace may have forgotten
to restore the ITS.

Exit silently and allow irqbypass configuration to succeed. As a reward
for ingenuity, LPIs are demoted to software injection.

Tested-by: default avatarSudheer Dantuluri <dantuluris@google.com>
Fixes: 196b1364 ("KVM: arm/arm64: GICv4: Wire mapping/unmapping of VLPIs in VFIO irq bypass")
Acked-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250226183124.82094-4-oliver.upton@linux.dev


Signed-off-by: default avatarOliver Upton <oliver.upton@linux.dev>
parent d0b79563

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

+10 −5
Original line number Diff line number Diff line
@@ -415,7 +415,7 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq, 
	struct vgic_irq *irq;

	struct its_vlpi_map map;

	unsigned long flags;

	int ret;

	int ret = 0;



	if (!vgic_supports_direct_msis(kvm))

		return 0;
@@ -430,10 +430,15 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq, 


	mutex_lock(&its->its_lock);



	/* Perform the actual DevID/EventID -> LPI translation. */

	ret = vgic_its_resolve_lpi(kvm, its, irq_entry->msi.devid,

				   irq_entry->msi.data, &irq);

	if (ret)

	/*

	 * Perform the actual DevID/EventID -> LPI translation.

	 *

	 * Silently exit if translation fails as the guest (or userspace!) has

	 * managed to do something stupid. Emulated LPI injection will still

	 * work if the guest figures itself out at a later time.

	 */

	if (vgic_its_resolve_lpi(kvm, its, irq_entry->msi.devid,

				 irq_entry->msi.data, &irq))

		goto out;



	/* Silently exit if the vLPI is already mapped */