Merge branch 'xsk-support-redirect-to-any-socket-bound-to-the-same-umem'

Magnus Karlsson says:

====================
xsk: support redirect to any socket bound to the same umem

This patch set adds support for directing a packet to any socket bound
to the same umem. This makes it possible to use the XDP program to
select what socket the packet should be received on. The user can
populate the XSKMAP with various sockets and as long as they share the
same umem, the XDP program can pick any one of them.

The implementation is straight-forward. Instead of testing that the
incoming packet is targeting the same device and queue id as the
socket is bound to, just check that the umem the packet was received
on is the same as the socket we want it to be received on. This
guarantees that the redirect is legal as it is already in the correct
umem.

Patch #1 implements the feature and patch #2 adds documentation.

Thanks: Magnus
====================

Link: https://lore.kernel.org/r/20240205123553.22180-1-magnus.karlsson@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 23 insertions, 15 deletions

diff --git a/Documentation/networking/af_xdp.rst b/Documentation/networking/af_xdp.rst
index dceeb0d763aa..72da7057e4cf 100644
--- a/Documentation/networking/af_xdp.rst
+++ b/Documentation/networking/af_xdp.rst
@@ -329,23 +329,24 @@ XDP_SHARED_UMEM option and provide the initial socket's fd in the
 sxdp_shared_umem_fd field as you registered the UMEM on that
 socket. These two sockets will now share one and the same UMEM.
 
-There is no need to supply an XDP program like the one in the previous
-case where sockets were bound to the same queue id and
-device. Instead, use the NIC's packet steering capabilities to steer
-the packets to the right queue. In the previous example, there is only
-one queue shared among sockets, so the NIC cannot do this steering. It
-can only steer between queues.
-
-In libbpf, you need to use the xsk_socket__create_shared() API as it
-takes a reference to a FILL ring and a COMPLETION ring that will be
-created for you and bound to the shared UMEM. You can use this
-function for all the sockets you create, or you can use it for the
-second and following ones and use xsk_socket__create() for the first
-one. Both methods yield the same result.
+In this case, it is possible to use the NIC's packet steering
+capabilities to steer the packets to the right queue. This is not
+possible in the previous example as there is only one queue shared
+among sockets, so the NIC cannot do this steering as it can only steer
+between queues.
+
+In libxdp (or libbpf prior to version 1.0), you need to use the
+xsk_socket__create_shared() API as it takes a reference to a FILL ring
+and a COMPLETION ring that will be created for you and bound to the
+shared UMEM. You can use this function for all the sockets you create,
+or you can use it for the second and following ones and use
+xsk_socket__create() for the first one. Both methods yield the same
+result.
 
 Note that a UMEM can be shared between sockets on the same queue id
 and device, as well as between queues on the same device and between
-devices at the same time.
+devices at the same time. It is also possible to redirect to any
+socket as long as it is bound to the same umem with XDP_SHARED_UMEM.
 
 XDP_USE_NEED_WAKEUP bind flag
 -----------------------------
@@ -822,6 +823,10 @@ A: The short answer is no, that is not supported at the moment. The
    switch, or other distribution mechanism, in your NIC to direct
    traffic to the correct queue id and socket.
 
+   Note that if you are using the XDP_SHARED_UMEM option, it is
+   possible to switch traffic between any socket bound to the same
+   umem.
+
 Q: My packets are sometimes corrupted. What is wrong?
 
 A: Care has to be taken not to feed the same buffer in the UMEM into
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 1eadfac03cc4..a339e9a1b557 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -313,10 +313,13 @@ static bool xsk_is_bound(struct xdp_sock *xs)
 
 static int xsk_rcv_check(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
 {
+	struct net_device *dev = xdp->rxq->dev;
+	u32 qid = xdp->rxq->queue_index;
+
 	if (!xsk_is_bound(xs))
 		return -ENXIO;
 
-	if (xs->dev != xdp->rxq->dev || xs->queue_id != xdp->rxq->queue_index)
+	if (!dev->_rx[qid].pool || xs->umem != dev->_rx[qid].pool->umem)
 		return -EINVAL;
 
 	if (len > xsk_pool_get_rx_frame_size(xs->pool) && !xs->sg) {