virtio: rng: Check notifier helpers for VIRTIO_CONFIG_IRQ_IDX

Since the driver doesn't support interrupts, we must return early when
index is set to VIRTIO_CONFIG_IRQ_IDX.  Basically the same thing Viresh
did for "91208dd297f2 virtio: i2c: Check notifier helpers for
VIRTIO_CONFIG_IRQ_IDX".

Fixes: 544f027 ("virtio: introduce macro VIRTIO_CONFIG_IRQ_IDX")
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Message-Id: <20231025171841.3379663-1-mathieu.poirier@linaro.org>
Tested-by: Leo Yan <leo.yan@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/vhost-user-rng.c

@@ -129,13 +129,29 @@ static void vu_rng_guest_notifier_mask(VirtIODevice *vdev, int idx, bool mask)
 {
     VHostUserRNG *rng = VHOST_USER_RNG(vdev);
 
+    /*
+     * We don't support interrupts, return early if index is set to
+     * VIRTIO_CONFIG_IRQ_IDX.
+     */
+    if (idx == VIRTIO_CONFIG_IRQ_IDX) {
+        return;
+    }
+
     vhost_virtqueue_mask(&rng->vhost_dev, vdev, idx, mask);
 }
 
 static bool vu_rng_guest_notifier_pending(VirtIODevice *vdev, int idx)
 {
     VHostUserRNG *rng = VHOST_USER_RNG(vdev);
 
+    /*
+     * We don't support interrupts, return early if index is set to
+     * VIRTIO_CONFIG_IRQ_IDX.
+     */
+    if (idx == VIRTIO_CONFIG_IRQ_IDX) {
+        return false;
+    }
+
     return vhost_virtqueue_pending(&rng->vhost_dev, idx);
 }