On Mon, Nov 30, 2015 at 10:34:07AM +0200, Michael S. Tsirkin wrote:
> We know vring num is a power of 2, so use &
> to mask the high bits.
>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> drivers/vhost/vhost.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 080422f..85f0f0a 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1366,10 +1366,12 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> /* Only get avail ring entries after they have been exposed by guest. */
> smp_rmb();
>
> + }
> +
Oops. This sneaked in from an unrelated patch.
Pls ignore, will repost.
> /* Grab the next descriptor number they're advertising, and increment
> * the index we've seen. */
> if (unlikely(__get_user(ring_head,
> - &vq->avail->ring[last_avail_idx % vq->num]))) {
> + &vq->avail->ring[last_avail_idx & (vq->num - 1)]))) {
> vq_err(vq, "Failed to read head: idx %d address %p\n",
> last_avail_idx,
> &vq->avail->ring[last_avail_idx % vq->num]);
> @@ -1489,7 +1491,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
> u16 old, new;
> int start;
>
> - start = vq->last_used_idx % vq->num;
> + start = vq->last_used_idx & (vq->num - 1);
> used = vq->used->ring + start;
> if (count == 1) {
> if (__put_user(heads[0].id, &used->id)) {
> @@ -1531,7 +1533,7 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
> {
> int start, n, r;
>
> - start = vq->last_used_idx % vq->num;
> + start = vq->last_used_idx & (vq->num - 1);
> n = vq->num - start;
> if (n < count) {
> r = __vhost_add_used_n(vq, heads, n);
> --
> MST
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