[PATCH 2/2] KVM: arm64: vgic-v3: Don't drop a pending LPI mapped with LPIs disabled

[Fuad Tabba <fuad.tabba@linux.dev>]

When an LPI is mapped, or restored with the ITS tables,
vgic_v3_lpi_sync_pending_status() moves its bit in the target
redistributor's pending table into the LPI's pending latch. Enabling
LPIs on that redistributor resets the latch of every LPI that targets it
from the table (its_sync_lpi_pending_table()), which no longer has the
bit. So an LPI mapped while its redistributor has LPIs disabled loses
its pending state, and the guest never takes it.

While the redistributor has LPIs disabled, copy the bit into the latch
rather than move it, so that enabling LPIs reads it again from the
table. It's still copied into the latch, since saving the pending tables
would otherwise write the empty latch over the bit.

Fixes: 06bd5359549d7 ("KVM: arm64: vgic-its: Read config and pending bit in add_lpi()")
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arch/arm64/kvm/vgic/vgic-v3.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
index 346bacb3198f2..65b77fb35be37 100644
--- a/arch/arm64/kvm/vgic/vgic-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-v3.c
@@ -552,7 +552,8 @@ int vgic_v3_lpi_sync_pending_status(struct kvm *kvm, struct vgic_irq *irq)
 	irq->pending_latch = status;
 	vgic_queue_irq_unlock(vcpu->kvm, irq, flags);
 
-	if (status) {
+	/* Enabling LPIs resets the latch from the table: leave the bit for it */
+	if (status && vgic_lpis_enabled(vcpu)) {
 		/* clear consumed data */
 		val &= ~(1 << bit_nr);
 		ret = vgic_write_guest_lock(kvm, ptr, &val, 1);
-- 
2.47.3