[PATCH 3.2 49/95] virtio_balloon: init 1st buffer in stats vq
From: Ben Hutchings
Date: Sun Jul 16 2017 - 10:51:55 EST
3.2.91-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Ladi Prosek <lprosek@xxxxxxxxxx>
commit fc8653228c8588a120f6b5dad6983b7b61ff669e upstream.
When init_vqs runs, virtio_balloon.stats is either uninitialized or
contains stale values. The host updates its state with garbage data
because it has no way of knowing that this is just a marker buffer
used for signaling.
This patch updates the stats before pushing the initial buffer.
Alternative fixes:
* Push an empty buffer in init_vqs. Not easily done with the current
virtio implementation and violates the spec "Driver MUST supply the
same subset of statistics in all buffers submitted to the statsq".
* Push a buffer with invalid tags in init_vqs. Violates the same
spec clause, plus "invalid tag" is not really defined.
Note: the spec says:
When using the legacy interface, the device SHOULD ignore all values in
the first buffer in the statsq supplied by the driver after device
initialization. Note: Historically, drivers supplied an uninitialized
buffer in the first buffer.
Unfortunately QEMU does not seem to implement the recommendation
even for the legacy interface.
Signed-off-by: Ladi Prosek <lprosek@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
drivers/virtio/virtio_balloon.c | 2 ++
1 file changed, 2 insertions(+)
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -320,6 +320,8 @@ static int virtballoon_probe(struct virt
* Prime this virtqueue with one buffer so the hypervisor can
* use it to signal us later.
*/
+ update_balloon_stats(vb);
+
sg_init_one(&sg, vb->stats, sizeof vb->stats);
if (virtqueue_add_buf(vb->stats_vq, &sg, 1, 0, vb) < 0)
BUG();