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virtio: order used ring after used index read

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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
This commit is contained in:
Michael S. Tsirkin 2009-10-25 15:28:53 +02:00 committed by Rusty Russell
parent 0b22bd0ba0
commit 2d61ba9503
1 changed files with 3 additions and 0 deletions
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3
drivers/virtio/virtio_ring.c
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@ -285,6 +285,9 @@ static void *vring_get_buf(struct virtqueue *_vq, unsigned int *len)
return NULL; 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; 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; *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;