[Qemu-devel] [PATCH 8/9] virtio: check for vring setup in virtio_queue_update_used_idx

[Paolo Bonzini <pbonzini@redhat.com>]

If the vring has not been set up, it is not necessary for vring_used_idx
to do anything (as is already the case when the caller is virtio_load).
This is harmless for now, but it will be a problem when the
MemoryRegionCache has not been set up.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/virtio/virtio.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 32bf364..23fac1e 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2154,7 +2154,9 @@ void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx)
 
 void virtio_queue_update_used_idx(VirtIODevice *vdev, int n)
 {
-    vdev->vq[n].used_idx = vring_used_idx(&vdev->vq[n]);
+    if (vdev->vq[n].vring.desc) {
+        vdev->vq[n].used_idx = vring_used_idx(&vdev->vq[n]);
+    }
 }
 
 void virtio_queue_invalidate_signalled_used(VirtIODevice *vdev, int n)
-- 
1.8.3.1