On 11/30/2015 10:15 AM, Michael S. Tsirkin wrote:
> We know vring num is a power of 2, so use &
> to mask the high bits.

Makes a lot of sense and virtio_ring.c seems to use the same logic.

Acked-by: Christian Borntraeger <borntrae...@de.ibm.com>

> 
> Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
> ---
> 
> Changes from v1: drop an unrelated chunk
> 
>  drivers/vhost/vhost.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 080422f..ad2146a 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1369,7 +1369,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
>       /* 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 +1489,7 @@ 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 +1531,7 @@ 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);
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Reply via email to