[Qemu-devel] [PATCH] virtio: fix vring->inuse recalc after migr

[Halil Pasic]

Correct recalculation of vring->inuse after migration for
the corner case where the avail_idx has already wrapped
but used_idx not yet.

Signed-off-by: Halil Pasic <address@hidden>
Fixes: bccdef6b ("virtio: recalculate vq->inuse after migration")
CC: address@hidden
---

I think we could also change the type of inuse to uint16_t.
Would this be considered a good idea?
---
 hw/virtio/virtio.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 1af2de2..089c6f6 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -1855,9 +1855,12 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int 
version_id)
             /*
              * Some devices migrate VirtQueueElements that have been popped
              * from the avail ring but not yet returned to the used ring.
+             * Cast to uint16_t is OK because max ring size is 0x8000. Thus
+             * no the size of largest array indexable by an integral type
+             * can not be represented by the same type problem.
              */
-            vdev->vq[i].inuse = vdev->vq[i].last_avail_idx -
-                                vdev->vq[i].used_idx;
+            vdev->vq[i].inuse = (uint16_t)(vdev->vq[i].last_avail_idx -
+                                vdev->vq[i].used_idx);
             if (vdev->vq[i].inuse > vdev->vq[i].vring.num) {
                 error_report("VQ %d size 0x%x < last_avail_idx 0x%x - "
                              "used_idx 0x%x",
-- 
2.8.4