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authorMichael S. Tsirkin <mst@redhat.com>2009-10-25 15:28:53 +0200
committerRusty Russell <rusty@rustcorp.com.au>2009-10-29 08:50:37 +1030
commit2d61ba95034f1abbdec7729d52c740870a5eddb6 (patch)
treeec51d4cba4240af6011f4fabfda06a21532761da /drivers/virtio
parent0b22bd0ba0d500ab40e7673c591c594ec5447342 (diff)
downloadlwn-2d61ba95034f1abbdec7729d52c740870a5eddb6.tar.gz
lwn-2d61ba95034f1abbdec7729d52c740870a5eddb6.zip
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 <mst@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Cc: stable@kernel.org
Diffstat (limited to 'drivers/virtio')
-rw-r--r--drivers/virtio/virtio_ring.c3
1 files changed, 3 insertions, 0 deletions
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;