netdevsim: add loopback support

Support device loopback. Apparently this mode has been historically
supported by the toeplitz test and I don't have any HW which lets
me test the conversion..

Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20251120021024.2944527-12-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index 2b713db16cd0e3df306caec7281fccb911036757..6927c1962277aa916ae646f4235f8ab58ec40e21 100644 (file)
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -133,15 +133,21 @@ static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
        if (!nsim_ipsec_tx(ns, skb))
                goto out_drop_any;
 
-       peer_ns = rcu_dereference(ns->peer);
-       if (!peer_ns)
-               goto out_drop_any;
+       /* Check if loopback mode is enabled */
+       if (dev->features & NETIF_F_LOOPBACK) {
+               peer_ns = ns;
+               peer_dev = dev;
+       } else {
+               peer_ns = rcu_dereference(ns->peer);
+               if (!peer_ns)
+                       goto out_drop_any;
+               peer_dev = peer_ns->netdev;
+       }
 
        dr = nsim_do_psp(skb, ns, peer_ns, &psp_ext);
        if (dr)
                goto out_drop_free;
 
-       peer_dev = peer_ns->netdev;
        rxq = skb_get_queue_mapping(skb);
        if (rxq >= peer_dev->num_rx_queues)
                rxq = rxq % peer_dev->num_rx_queues;
@@ -976,7 +982,8 @@ static void nsim_setup(struct net_device *dev)
                            NETIF_F_FRAGLIST |
                            NETIF_F_HW_CSUM |
                            NETIF_F_LRO |
-                           NETIF_F_TSO;
+                           NETIF_F_TSO |
+                           NETIF_F_LOOPBACK;
        dev->pcpu_stat_type = NETDEV_PCPU_STAT_DSTATS;
        dev->max_mtu = ETH_MAX_MTU;
        dev->xdp_features = NETDEV_XDP_ACT_BASIC | NETDEV_XDP_ACT_HW_OFFLOAD;