KVM: arm64: vgic-its: Clear ITE when DISCARD frees an ITE

When DISCARD frees an ITE, it does not invalidate the
corresponding ITE. In the scenario of continuous saves and
restores, there may be a situation where an ITE is not saved
but is restored. This is unreasonable and may cause restore
to fail. This patch clears the corresponding ITE when DISCARD
frees an ITE.

Cc: stable@vger.kernel.org
Fixes: eff484e ("KVM: arm64: vgic-its: ITT save and restore")
Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
[Jing: Update with entry write helper]
Signed-off-by: Jing Zhang <jingzhangos@google.com>
Link: https://lore.kernel.org/r/20241107214137.428439-6-jingzhangos@google.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: Kunkun Jiang

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

@@ -782,6 +782,9 @@ static int vgic_its_cmd_handle_discard(struct kvm *kvm, struct vgic_its *its,
 
 	ite = find_ite(its, device_id, event_id);
 	if (ite && its_is_collection_mapped(ite->collection)) {
+		struct its_device *device = find_its_device(its, device_id);
+		int ite_esz = vgic_its_get_abi(its)->ite_esz;
+		gpa_t gpa = device->itt_addr + ite->event_id * ite_esz;
 		/*
 		 * Though the spec talks about removing the pending state, we
 		 * don't bother here since we clear the ITTE anyway and the
@@ -790,7 +793,8 @@ static int vgic_its_cmd_handle_discard(struct kvm *kvm, struct vgic_its *its,
 		vgic_its_invalidate_cache(its);
 
 		its_free_ite(kvm, ite);
-		return 0;
+
+		return vgic_its_write_entry_lock(its, gpa, 0, ite_esz);
 	}
 
 	return E_ITS_DISCARD_UNMAPPED_INTERRUPT;