| From | Ben Hutchings <> | Date | Sun, 16 Jul 2017 14:56:38 +0100 | Subject | [PATCH 3.2 49/95] virtio_balloon: init 1st buffer in stats vq |
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3.2.91-rc1 review patch. If anyone has any objections, please let me know.
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From: Ladi Prosek <lprosek@redhat.com>
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@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- 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();
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