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 initializes all tags with U16_MAX which is guaranteed to
be ignored by the host.
The alternative fix would be to push an empty buffer in init_vqs but
that's not easily done with the current virtio implementation and
would still not eliminate the invariant that update_balloon_stats
has to update all VIRTIO_BALLOON_S_NR fields.
Signed-off-by: Ladi Prosek <lprosek@xxxxxxxxxx>
---
drivers/virtio/virtio_balloon.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 4e11915..d34f56f 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -423,12 +423,16 @@ static int init_vqs(struct virtio_balloon *vb)
vb->deflate_vq = vqs[1];
if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
struct scatterlist sg;
+ int idx;
vb->stats_vq = vqs[2];
/*
* Prime this virtqueue with one buffer so the hypervisor can
* use it to signal us later (it can't be broken yet!).
*/
+ for (idx = 0; idx < VIRTIO_BALLOON_S_NR; idx++)
+ update_stat(vb, idx, U16_MAX, 0);
+
sg_init_one(&sg, vb->stats, sizeof vb->stats);
if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
< 0)
--
2.7.4
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