netdev - [PATCH net] virtio-net: fix incorrect flags recording in big mode

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Message-Id: <20250919013450.111424-1-xuanzhuo@linux.alibaba.com>
Date: Fri, 19 Sep 2025 09:34:50 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: netdev@...r.kernel.org
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Heng Qi <hengqi@...ux.alibaba.com>,
	virtualization@...ts.linux.dev
Subject: [PATCH net] virtio-net: fix incorrect flags recording in big mode

The purpose of commit 703eec1b2422 ("virtio_net: fixing XDP for fully
checksummed packets handling") is to record the flags in advance, as
their value may be overwritten in the XDP case. However, the flags
recorded under big mode are incorrect, because in big mode, the passed
buf does not point to the rx buffer, but rather to the page of the
submitted buffer. This commit fixes this issue.

For the small mode, the commit c11a49d58ad2 ("virtio_net: Fix mismatched
buf address when unmapping for small packets") fixed it.

Fixes: 703eec1b2422 ("virtio_net: fixing XDP for fully checksummed packets handling")
Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
---
 drivers/net/virtio_net.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 975bdc5dab84..6e6e74390955 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2630,13 +2630,19 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
 	 */
 	flags = ((struct virtio_net_common_hdr *)buf)->hdr.flags;
 
-	if (vi->mergeable_rx_bufs)
+	if (vi->mergeable_rx_bufs) {
 		skb = receive_mergeable(dev, vi, rq, buf, ctx, len, xdp_xmit,
 					stats);
-	else if (vi->big_packets)
+	} else if (vi->big_packets) {
+		void *p;
+
+		p = page_address((struct page *)buf);
+		flags = ((struct virtio_net_common_hdr *)p)->hdr.flags;
+
 		skb = receive_big(dev, vi, rq, buf, len, stats);
-	else
+	} else {
 		skb = receive_small(dev, vi, rq, buf, ctx, len, xdp_xmit, stats);
+	}
 
 	if (unlikely(!skb))
 		return;
-- 
2.32.0.3.g01195cf9f