mlxsw: spectrum: Trap loop-backed packets

One of the conditions to generate an ICMP Redirect Message is that "the
packet is being forwarded out the same physical interface that it was
received from" (RFC 1812).

Therefore, we need to be able to trap such packets and let the kernel
decide what to do with them.

For each RIF, enable the loop-back filter, which will raise the LBERROR
trap whenever the ingress RIF equals the egress RIF.

Fixes: 99724c1 ("mlxsw: spectrum: Introduce support for router interfaces")
Reported-by: Ilan Tayari <ilant@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/reg.h

@@ -3383,6 +3383,15 @@ MLXSW_ITEM32(reg, ritr, ipv4_fe, 0x04, 29, 1);
  */
 MLXSW_ITEM32(reg, ritr, ipv6_fe, 0x04, 28, 1);
 
+/* reg_ritr_lb_en
+ * Loop-back filter enable for unicast packets.
+ * If the flag is set then loop-back filter for unicast packets is
+ * implemented on the RIF. Multicast packets are always subject to
+ * loop-back filtering.
+ * Access: RW
+ */
+MLXSW_ITEM32(reg, ritr, lb_en, 0x04, 24, 1);
+
 /* reg_ritr_virtual_router
  * Virtual router ID associated with the router interface.
  * Access: RW
@@ -3484,6 +3493,7 @@ static inline void mlxsw_reg_ritr_pack(char *payload, bool enable,
 	mlxsw_reg_ritr_op_set(payload, op);
 	mlxsw_reg_ritr_rif_set(payload, rif);
 	mlxsw_reg_ritr_ipv4_fe_set(payload, 1);
+	mlxsw_reg_ritr_lb_en_set(payload, 1);
 	mlxsw_reg_ritr_mtu_set(payload, mtu);
 	mlxsw_reg_ritr_if_mac_memcpy_to(payload, mac);
 }

drivers/net/ethernet/mellanox/mlxsw/spectrum.c

@@ -2658,6 +2658,11 @@ static const struct mlxsw_rx_listener mlxsw_sp_rx_listener[] = {
 		.local_port = MLXSW_PORT_DONT_CARE,
 		.trap_id = MLXSW_TRAP_ID_TTLERROR,
 	},
+	{
+		.func = mlxsw_sp_rx_listener_func,
+		.local_port = MLXSW_PORT_DONT_CARE,
+		.trap_id = MLXSW_TRAP_ID_LBERROR,
+	},
 	{
 		.func = mlxsw_sp_rx_listener_func,
 		.local_port = MLXSW_PORT_DONT_CARE,

drivers/net/ethernet/mellanox/mlxsw/trap.h

@@ -58,6 +58,7 @@ enum {
 	MLXSW_TRAP_ID_ARPUC = 0x51,
 	MLXSW_TRAP_ID_MTUERROR = 0x52,
 	MLXSW_TRAP_ID_TTLERROR = 0x53,
+	MLXSW_TRAP_ID_LBERROR = 0x54,
 	MLXSW_TRAP_ID_OSPF = 0x55,
 	MLXSW_TRAP_ID_IP2ME = 0x5F,
 	MLXSW_TRAP_ID_RTR_INGRESS0 = 0x70,