From: Magnus Karlsson magnus.karlsson@intel.com
[ 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@intel.com Acked-by: Toke Høiland-Jørgensen toke@redhat.com Link: https://lore.kernel.org/r/20221220185903.1105011-1-sbohrer@cloudflare.com Link: https://lore.kernel.org/all/20210624160609.292325-1-toke@redhat.com/ Acked-by: Michael S. Tsirkin mst@redhat.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/virtio_net.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 9222be208aba..a5ec81c76155 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -1580,13 +1580,13 @@ 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)) {