mlxsw: spectrum: Fix ECN marking in tunnel decapsulation

Cited commit changed the behavior of the software data path with regards
to the ECN marking of decapsulated packets. However, the commit did not
change other callers of __INET_ECN_decapsulate(), namely mlxsw. The
driver is using the function in order to ensure that the hardware and
software data paths act the same with regards to the ECN marking of
decapsulated packets.

The discrepancy was uncovered by commit 5aa3c334 ("selftests:
forwarding: vxlan_bridge_1d: Fix vxlan ecn decapsulate value") that
aligned the selftest to the new behavior. Without this patch the
selftest passes when used with veth pairs, but fails when used with
mlxsw netdevs.

Fix this by instructing the device to propagate the ECT(1) mark from the
outer header to the inner header when the inner header is ECT(0), for
both NVE and IP-in-IP tunnels.

A helper is added in order not to duplicate the code between both tunnel
types.

Fixes: b7237487 ("tunnel: Propagate ECT(1) when decapsulating as recommended by RFC6040")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -21,6 +21,7 @@
 #include <net/red.h>
 #include <net/vxlan.h>
 #include <net/flow_offload.h>
+#include <net/inet_ecn.h>
 
 #include "port.h"
 #include "core.h"
@@ -347,6 +348,20 @@ struct mlxsw_sp_port_type_speed_ops {
 	u32 (*ptys_proto_cap_masked_get)(u32 eth_proto_cap);
 };
 
+static inline u8 mlxsw_sp_tunnel_ecn_decap(u8 outer_ecn, u8 inner_ecn,
+					   bool *trap_en)
+{
+	bool set_ce = false;
+
+	*trap_en = !!__INET_ECN_decapsulate(outer_ecn, inner_ecn, &set_ce);
+	if (set_ce)
+		return INET_ECN_CE;
+	else if (outer_ecn == INET_ECN_ECT_1 && inner_ecn == INET_ECN_ECT_0)
+		return INET_ECN_ECT_1;
+	else
+		return inner_ecn;
+}
+
 static inline struct net_device *
 mlxsw_sp_bridge_vxlan_dev_find(struct net_device *br_dev)
 {

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

@@ -335,12 +335,11 @@ static int mlxsw_sp_ipip_ecn_decap_init_one(struct mlxsw_sp *mlxsw_sp,
 					    u8 inner_ecn, u8 outer_ecn)
 {
 	char tidem_pl[MLXSW_REG_TIDEM_LEN];
-	bool trap_en, set_ce = false;
 	u8 new_inner_ecn;
+	bool trap_en;
 
-	trap_en = __INET_ECN_decapsulate(outer_ecn, inner_ecn, &set_ce);
-	new_inner_ecn = set_ce ? INET_ECN_CE : inner_ecn;
-
+	new_inner_ecn = mlxsw_sp_tunnel_ecn_decap(outer_ecn, inner_ecn,
+						  &trap_en);
 	mlxsw_reg_tidem_pack(tidem_pl, outer_ecn, inner_ecn, new_inner_ecn,
 			     trap_en, trap_en ? MLXSW_TRAP_ID_DECAP_ECN0 : 0);
 	return mlxsw_reg_write(mlxsw_sp->core, MLXSW_REG(tidem), tidem_pl);

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

@@ -909,12 +909,11 @@ static int __mlxsw_sp_nve_ecn_decap_init(struct mlxsw_sp *mlxsw_sp,
 					 u8 inner_ecn, u8 outer_ecn)
 {
 	char tndem_pl[MLXSW_REG_TNDEM_LEN];
-	bool trap_en, set_ce = false;
 	u8 new_inner_ecn;
+	bool trap_en;
 
-	trap_en = !!__INET_ECN_decapsulate(outer_ecn, inner_ecn, &set_ce);
-	new_inner_ecn = set_ce ? INET_ECN_CE : inner_ecn;
-
+	new_inner_ecn = mlxsw_sp_tunnel_ecn_decap(outer_ecn, inner_ecn,
+						  &trap_en);
 	mlxsw_reg_tndem_pack(tndem_pl, outer_ecn, inner_ecn, new_inner_ecn,
 			     trap_en, trap_en ? MLXSW_TRAP_ID_DECAP_ECN0 : 0);
 	return mlxsw_reg_write(mlxsw_sp->core, MLXSW_REG(tndem), tndem_pl);