[PATCH v1] KVM: arm64: vgic-v4: Don't forward an LPI with no target vCPU

[Fuad Tabba]

Hi Marc,

On Mon, 12 Oct 2026 12:18:51 +0100, Marc Zyngier <maz at kernel.org> wrote:
[...]
> Isn't the core problem that we don't correctly handle the UNPRED
> double mapping of the same LPI? I'd rather we attack the issue at the
> source instead of papering over the consequences.
>
> I hacked the following, which is obviously untested. Can you give it a
> go?

With your diff on rc3, the second MAPTI is dropped, and forwarding the
vfio-pci MSI to its event leaves the host up.

However, a vgic_irq outlives its ITE while the LPI is pending on a
vCPU, so the check also drops a legitimate remap: a guest that
DISCARDs a pending LPI and then maps it again loses the new mapping.
On QEMU, rc3 (baseline) keeps it and your diff drops it.
vgic_its_restore_ite() also goes through vgic_add_lpi(), so restoring
tables that hold a double mapping fails with -EEXIST.

v2, which I'm still testing, drops the second mapping at MAPTI too,
but tracks in the vgic_irq whether an ITE maps it and checks that
instead. A restore keeps the first ITE and drops the duplicate. I'll
send it tomorrow.

Cheers,
/fuad