This is a note to let you know that I've just added the patch titled
virtio-net: execute xdp_do_flush() before napi_complete_done()
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
virtio-net-execute-xdp_do_flush-before-napi_complete.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 840d3ce1fdaa05874c6ea40d8362eafec4a3884d
Author: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
Date: Wed Jan 25 08:48:59 2023 +0100
virtio-net: execute xdp_do_flush() before napi_complete_done()
[ Upstream commit ad7e615f646c9b5b2cf655cdfb9d91a28db4f25a ]
Make sure that xdp_do_flush() is always executed before
napi_complete_done(). This is important for two reasons. First, a
redirect to an XSKMAP assumes that a call to xdp_do_redirect() from
napi context X on CPU Y will be followed by a xdp_do_flush() from the
same napi context and CPU. This is not guaranteed if the
napi_complete_done() is executed before xdp_do_flush(), as it tells
the napi logic that it is fine to schedule napi context X on another
CPU. Details from a production system triggering this bug using the
veth driver can be found following the first link below.
The second reason is that the XDP_REDIRECT logic in itself relies on
being inside a single NAPI instance through to the xdp_do_flush() call
for RCU protection of all in-kernel data structures. Details can be
found in the second link below.
Fixes: 186b3c998c50 ("virtio-net: support XDP_REDIRECT")
Signed-off-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
Acked-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20221220185903.1105011-1-sbohrer@xxxxxxxxxxxxxx
Link: https://lore.kernel.org/all/20210624160609.292325-1-toke@xxxxxxxxxx/
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c942cd6a2c65..0605c28c684b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1525,13 +1525,13 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
received = virtnet_receive(rq, budget, &xdp_xmit);
+ if (xdp_xmit & VIRTIO_XDP_REDIR)
+ xdp_do_flush();
+
/* Out of packets? */
if (received < budget)
virtqueue_napi_complete(napi, rq->vq, received);
- if (xdp_xmit & VIRTIO_XDP_REDIR)
- xdp_do_flush();
-
if (xdp_xmit & VIRTIO_XDP_TX) {
sq = virtnet_xdp_get_sq(vi);
if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
