xsk: Add shared umem support between devices

Add support to share a umem between different devices. This mode
can be invoked with the XDP_SHARED_UMEM bind flag. Previously,
sharing was only supported within the same device. Note that when
sharing a umem between devices, just as in the case of sharing a
umem between queue ids, you need to create a fill ring and a
completion ring and tie them to the socket (with two setsockopts,
one for each ring) before you do the bind with the
XDP_SHARED_UMEM flag. This so that the single-producer
single-consumer semantics of the rings can be upheld.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Björn Töpel <bjorn.topel@intel.com>
Link: https://lore.kernel.org/bpf/1598603189-32145-13-git-send-email-magnus.karlsson@intel.com

net/xdp/xsk.c

@@ -701,14 +701,11 @@ static int xsk_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
 			sockfd_put(sock);
 			goto out_unlock;
 		}
-		if (umem_xs->dev != dev) {
-			err = -EINVAL;
-			sockfd_put(sock);
-			goto out_unlock;
-		}
 
-		if (umem_xs->queue_id != qid) {
-			/* Share the umem with another socket on another qid */
+		if (umem_xs->queue_id != qid || umem_xs->dev != dev) {
+			/* Share the umem with another socket on another qid
+			 * and/or device.
+			 */
 			xs->pool = xp_create_and_assign_umem(xs,
 							     umem_xs->umem);
 			if (!xs->pool) {