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 <borntraeger@xxxxxxxxxx> > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > --- > > 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); > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization