From 6918f8446eacec98afccae5b42c3511d5b23e028 Mon Sep 17 00:00:00 2001 From: Ladi Prosek Date: Thu, 23 Mar 2017 08:04:18 +0100 Subject: [PATCH] virtio_balloon: init 1st buffer in stats vq 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 Signed-off-by: Michael S. Tsirkin Signed-off-by: Ben Hutchings --- drivers/virtio/virtio_balloon.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index 2975c5089dac..1601e3eb3614 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -320,6 +320,8 @@ static int virtballoon_probe(struct virtio_device *vdev) * 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(); -- 2.39.2