vhost: replace % with & on data path

We know vring num is a power of 2, so use &
to mask the high bits.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 080422f..ad2146a 100644 (file)
--- 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);