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virtio: order used ring after used index read

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commit 2d61ba95034f1abbdec7729d52c740870a5eddb6 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Michael S. Tsirkin
2009-10-25 15:28:53 +02:00
committed by Greg Kroah-Hartman
parent bed2023563
commit 48fe10afb3
1 changed files with 3 additions and 0 deletions
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3
drivers/virtio/virtio_ring.c
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@@ -281,6 +281,9 @@ 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;