Revert "virtio_net: rx remove premapped failover code"

This reverts commit defd28a.

Recover the code to disable premapped mode.

Signed-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/20240906123137.108741-2-xuanzhuo@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: fengidri

drivers/net/virtio_net.c

@@ -356,6 +356,9 @@ struct receive_queue {
 	struct xdp_rxq_info xsk_rxq_info;
 
 	struct xdp_buff **xsk_buffs;
+
+	/* Do dma by self */
+	bool do_dma;
 };
 
 /* This structure can contain rss message with maximum settings for indirection table and keysize
@@ -885,7 +888,7 @@ static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
 	void *buf;
 
 	buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
-	if (buf)
+	if (buf && rq->do_dma)
 		virtnet_rq_unmap(rq, buf, *len);
 
 	return buf;
@@ -898,6 +901,11 @@ static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
 	u32 offset;
 	void *head;
 
+	if (!rq->do_dma) {
+		sg_init_one(rq->sg, buf, len);
+		return;
+	}
+
 	head = page_address(rq->alloc_frag.page);
 
 	offset = buf - head;
@@ -923,42 +931,44 @@ static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
 
 	head = page_address(alloc_frag->page);
 
-	dma = head;
+	if (rq->do_dma) {
+		dma = head;
+
+		/* new pages */
+		if (!alloc_frag->offset) {
+			if (rq->last_dma) {
+				/* Now, the new page is allocated, the last dma
+				 * will not be used. So the dma can be unmapped
+				 * if the ref is 0.
+				 */
+				virtnet_rq_unmap(rq, rq->last_dma, 0);
+				rq->last_dma = NULL;
+			}
 
-	/* new pages */
-	if (!alloc_frag->offset) {
-		if (rq->last_dma) {
-			/* Now, the new page is allocated, the last dma
-			 * will not be used. So the dma can be unmapped
-			 * if the ref is 0.
-			 */
-			virtnet_rq_unmap(rq, rq->last_dma, 0);
-			rq->last_dma = NULL;
-		}
+			dma->len = alloc_frag->size - sizeof(*dma);
 
-		dma->len = alloc_frag->size - sizeof(*dma);
+			addr = virtqueue_dma_map_single_attrs(rq->vq, dma + 1,
+							      dma->len, DMA_FROM_DEVICE, 0);
+			if (virtqueue_dma_mapping_error(rq->vq, addr))
+				return NULL;
 
-		addr = virtqueue_dma_map_single_attrs(rq->vq, dma + 1,
-						      dma->len, DMA_FROM_DEVICE, 0);
-		if (virtqueue_dma_mapping_error(rq->vq, addr))
-			return NULL;
+			dma->addr = addr;
+			dma->need_sync = virtqueue_dma_need_sync(rq->vq, addr);
 
-		dma->addr = addr;
-		dma->need_sync = virtqueue_dma_need_sync(rq->vq, addr);
+			/* Add a reference to dma to prevent the entire dma from
+			 * being released during error handling. This reference
+			 * will be freed after the pages are no longer used.
+			 */
+			get_page(alloc_frag->page);
+			dma->ref = 1;
+			alloc_frag->offset = sizeof(*dma);
 
-		/* Add a reference to dma to prevent the entire dma from
-		 * being released during error handling. This reference
-		 * will be freed after the pages are no longer used.
-		 */
-		get_page(alloc_frag->page);
-		dma->ref = 1;
-		alloc_frag->offset = sizeof(*dma);
+			rq->last_dma = dma;
+		}
 
-		rq->last_dma = dma;
+		++dma->ref;
 	}
 
-	++dma->ref;
-
 	buf = head + alloc_frag->offset;
 
 	get_page(alloc_frag->page);
@@ -975,9 +985,12 @@ static void virtnet_rq_set_premapped(struct virtnet_info *vi)
 	if (!vi->mergeable_rx_bufs && vi->big_packets)
 		return;
 
-	for (i = 0; i < vi->max_queue_pairs; i++)
-		/* error should never happen */
-		BUG_ON(virtqueue_set_dma_premapped(vi->rq[i].vq));
+	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)
@@ -2430,7 +2443,8 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
 
 	err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
 	if (err < 0) {
-		virtnet_rq_unmap(rq, buf, 0);
+		if (rq->do_dma)
+			virtnet_rq_unmap(rq, buf, 0);
 		put_page(virt_to_head_page(buf));
 	}
 
@@ -2544,7 +2558,8 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
 	ctx = mergeable_len_to_ctx(len + room, headroom);
 	err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
 	if (err < 0) {
-		virtnet_rq_unmap(rq, buf, 0);
+		if (rq->do_dma)
+			virtnet_rq_unmap(rq, buf, 0);
 		put_page(virt_to_head_page(buf));
 	}
 
@@ -5892,7 +5907,7 @@ static void free_receive_page_frags(struct virtnet_info *vi)
 	int i;
 	for (i = 0; i < vi->max_queue_pairs; i++)
 		if (vi->rq[i].alloc_frag.page) {
-			if (vi->rq[i].last_dma)
+			if (vi->rq[i].do_dma && vi->rq[i].last_dma)
 				virtnet_rq_unmap(&vi->rq[i], vi->rq[i].last_dma, 0);
 			put_page(vi->rq[i].alloc_frag.page);
 		}