From:   Jason Wang <jasowang@redhat.com>
To:     mst@redhat.com, jasowang@redhat.com
Cc:     virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Eli Cohen <elic@nvidia.com>
Subject: [PATCH net] virtio-net: enable big mode correctly
Date:   Thu, 25 Nov 2021 14:05:47 +0800
Message-Id: <20211125060547.11961-1-jasowang@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When VIRTIO_NET_F_MTU feature is not negotiated, we assume a very
large max_mtu. In this case, using small packet mode is not correct
since it may breaks the networking when MTU is grater than
ETH_DATA_LEN.

To have a quick fix, simply enable the big packet mode when
VIRTIO_NET_F_MTU is not negotiated. We can do optimization on top.

Reported-by: Eli Cohen <elic@nvidia.com>
Cc: Eli Cohen <elic@nvidia.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/net/virtio_net.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7c43bfc1ce44..83ae3ef5eb11 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3200,11 +3200,12 @@ static int virtnet_probe(struct virtio_device *vdev)
 		dev->mtu = mtu;
 		dev->max_mtu = mtu;
 
-		/* TODO: size buffers correctly in this case. */
-		if (dev->mtu > ETH_DATA_LEN)
-			vi->big_packets = true;
 	}
 
+	/* TODO: size buffers correctly in this case. */
+	if (dev->max_mtu > ETH_DATA_LEN)
+		vi->big_packets = true;
+
 	if (vi->any_header_sg)
 		dev->needed_headroom = vi->hdr_len;
 
-- 
2.25.1