On Thu, Aug 10, 2017 at 05:40:34PM +0100, Richard W.M. Jones wrote:
> If using indirect descriptors, you can make the total_sg as large as
> you want.
That would be a spec violation though, even if it happens to
work on current QEMU.
The spec says:
A driver MUST NOT create a descriptor chain longer than the Queue Size of the device.
What prompted this patch? Do we ever encounter this situation?
> If not, BUG is too serious because the function later
> returns -ENOSPC.
>
> Thanks Paolo Bonzini, Christoph Hellwig.
>
> Signed-off-by: Richard W.M. Jones <rjones@xxxxxxxxxx>
> ---
> drivers/virtio/virtio_ring.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 5e1b548828e6..27cbc1eab868 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -296,7 +296,6 @@ static inline int virtqueue_add(struct virtqueue *_vq,
> }
> #endif
>
> - BUG_ON(total_sg > vq->vring.num);
> BUG_ON(total_sg == 0);
>
> head = vq->free_head;
> @@ -305,8 +304,10 @@ static inline int virtqueue_add(struct virtqueue *_vq,
> * buffers, then go indirect. FIXME: tune this threshold */
> if (vq->indirect && total_sg > 1 && vq->vq.num_free)
> desc = alloc_indirect(_vq, total_sg, gfp);
> - else
> + else {
> desc = NULL;
> + WARN_ON_ONCE(total_sg > vq->vring.num && !vq->indirect);
> + }
>
> if (desc) {
> /* Use a single buffer which doesn't continue */
> --
> 2.13.1
