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[PATCH V2 2/2] virtio-balloon: correct used length

From: Jason Wang
Subject: [PATCH V2 2/2] virtio-balloon: correct used length
Date: Mon, 29 Nov 2021 11:08:41 +0800

Spec said:

"and len the total of bytes written into the buffer."

For inflateq, deflateq and statsq, we don't process in_sg so the used
length should be zero. For free_page_vq, tough the pages could be
changed by the device (in the destination), spec said:

"Note: len is particularly useful for drivers using untrusted buffers:
if a driver does not know exactly how much has been written by the
device, the driver would have to zero the buffer in advance to ensure
no data leakage occurs."

So 0 should be used as well here.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Changes since V1:
- use 0 as used length for free_page_vq
 hw/virtio/virtio-balloon.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 17de2558cb..9a4f491b54 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -231,7 +231,7 @@ static void balloon_stats_poll_cb(void *opaque)
-    virtqueue_push(s->svq, s->stats_vq_elem, s->stats_vq_offset);
+    virtqueue_push(s->svq, s->stats_vq_elem, 0);
     virtio_notify(vdev, s->svq);
     s->stats_vq_elem = NULL;
@@ -438,7 +438,7 @@ static void virtio_balloon_handle_output(VirtIODevice 
*vdev, VirtQueue *vq)
-        virtqueue_push(vq, elem, offset);
+        virtqueue_push(vq, elem, 0);
         virtio_notify(vdev, vq);
@@ -552,7 +552,7 @@ static bool get_free_page_hints(VirtIOBalloon *dev)
-    virtqueue_push(vq, elem, 1);
+    virtqueue_push(vq, elem, 0);
     return ret;

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