virtio-net: use the check_mergeable_len helper

Replace the current repeated code to check received length in mergeable
mode with the new check_mergeable_len helper.

Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://patch.msgid.link/20250630144212.48471-4-minhquangbui99@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: minhbq-99

drivers/net/virtio_net.c

@@ -2156,7 +2156,6 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
 				      struct virtnet_rq_stats *stats)
 {
 	struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
-	unsigned int headroom, tailroom, room;
 	struct skb_shared_info *shinfo;
 	unsigned int xdp_frags_truesz = 0;
 	unsigned int truesize;
@@ -2202,20 +2201,14 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
 		page = virt_to_head_page(buf);
 		offset = buf - page_address(page);
 
-		truesize = mergeable_ctx_to_truesize(ctx);
-		headroom = mergeable_ctx_to_headroom(ctx);
-		tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
-		room = SKB_DATA_ALIGN(headroom + tailroom);
-
-		xdp_frags_truesz += truesize;
-		if (unlikely(len > truesize - room)) {
+		if (check_mergeable_len(dev, ctx, len)) {
 			put_page(page);
-			pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
-				 dev->name, len, (unsigned long)(truesize - room));
-			DEV_STATS_INC(dev, rx_length_errors);
 			goto err;
 		}
 
+		truesize = mergeable_ctx_to_truesize(ctx);
+		xdp_frags_truesz += truesize;
+
 		frag = &shinfo->frags[shinfo->nr_frags++];
 		skb_frag_fill_page_desc(frag, page, offset, len);
 		if (page_is_pfmemalloc(page))
@@ -2429,18 +2422,12 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 	struct sk_buff *head_skb, *curr_skb;
 	unsigned int truesize = mergeable_ctx_to_truesize(ctx);
 	unsigned int headroom = mergeable_ctx_to_headroom(ctx);
-	unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
-	unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
 
 	head_skb = NULL;
 	u64_stats_add(&stats->bytes, len - vi->hdr_len);
 
-	if (unlikely(len > truesize - room)) {
-		pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
-			 dev->name, len, (unsigned long)(truesize - room));
-		DEV_STATS_INC(dev, rx_length_errors);
+	if (check_mergeable_len(dev, ctx, len))
 		goto err_skb;
-	}
 
 	if (unlikely(vi->xdp_enabled)) {
 		struct bpf_prog *xdp_prog;
@@ -2475,17 +2462,10 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 		u64_stats_add(&stats->bytes, len);
 		page = virt_to_head_page(buf);
 
-		truesize = mergeable_ctx_to_truesize(ctx);
-		headroom = mergeable_ctx_to_headroom(ctx);
-		tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
-		room = SKB_DATA_ALIGN(headroom + tailroom);
-		if (unlikely(len > truesize - room)) {
-			pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
-				 dev->name, len, (unsigned long)(truesize - room));
-			DEV_STATS_INC(dev, rx_length_errors);
+		if (check_mergeable_len(dev, ctx, len))
 			goto err_skb;
-		}
 
+		truesize = mergeable_ctx_to_truesize(ctx);
 		curr_skb  = virtnet_skb_append_frag(head_skb, curr_skb, page,
 						    buf, len, truesize);
 		if (!curr_skb)