virtio_net: disable premapped mode by default

Now, the premapped mode encounters some problem.

    http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540c0a@oracle.com

So we disable the premapped mode by default.
We can re-enable it in the future.

Fixes: f9dac92b ("virtio_ring: enable premapped mode whatever use_dma_api")
Reported-by: "Si-Wei Liu" <si-wei.liu@oracle.com>
Closes: http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540c0a@oracle.comSigned-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Takero Funaki <flintglass@gmail.com>
Link: https://patch.msgid.link/20240906123137.108741-4-xuanzhuo@linux.alibaba.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/virtio_net.c

@@ -977,22 +977,6 @@ static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
 	return buf;
 }
 
-static void virtnet_rq_set_premapped(struct virtnet_info *vi)
-{
-	int i;
-
-	/* disable for big mode */
-	if (!vi->mergeable_rx_bufs && vi->big_packets)
-		return;
-
-	for (i = 0; i < vi->max_queue_pairs; i++) {
-		if (virtqueue_set_dma_premapped(vi->rq[i].vq))
-			continue;
-
-		vi->rq[i].do_dma = true;
-	}
-}
-
 static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
 {
 	struct virtnet_info *vi = vq->vdev->priv;
@@ -6105,8 +6089,6 @@ static int init_vqs(struct virtnet_info *vi)
 	if (ret)
 		goto err_free;
 
-	virtnet_rq_set_premapped(vi);
-
 	cpus_read_lock();
 	virtnet_set_affinity(vi);
 	cpus_read_unlock();