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);
>
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