From 2d61ba95034f1abbdec7729d52c740870a5eddb6 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Sun, 25 Oct 2009 15:28:53 +0200 Subject: [PATCH] virtio: order used ring after used index read On SMP guests, reads from the ring might bypass used index reads. This causes guest crashes because host writes to used index to signal ring data readiness. Fix this by inserting rmb before used ring reads. Signed-off-by: Michael S. Tsirkin Signed-off-by: Rusty Russell Cc: stable@kernel.org --- drivers/virtio/virtio_ring.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index f53600580726..fbd2ecde93e4 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -285,6 +285,9 @@ static void *vring_get_buf(struct virtqueue *_vq, unsigned int *len) return NULL; } + /* Only get used array entries after they have been exposed by host. */ + rmb(); + i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id; *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;