mlxsw: spectrum: Mirror loopbacked packets instead of trapping them

When the ASIC detects that a unicast packet is routed through the same
router interface (RIF) from which it ingressed (iRIF == eRIF), it raises
a trap called loopback error (LBERROR).

Thus far, this trap was configured to send a sole copy of the packet to
the CPU so that ICMP redirect packets could be potentially generated by
the kernel.

This is problematic as the CPU cannot forward packets at 3.2Tb/s and
there are scenarios (e.g., "one-armed router") where iRIF == eRIF is not
an exception.

Solve this by changing the trap to send a copy of the packet to the CPU.
To prevent the kernel from forwarding the packet again, it is marked
with 'offload_l3_fwd_mark'.

The trap is configured in a trap group of its own with a dedicated
policer in order not to prevent packets trapped by other traps from
reaching the CPU.
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -5072,6 +5072,7 @@ enum mlxsw_reg_htgt_trap_group {
 	MLXSW_REG_HTGT_TRAP_GROUP_SP_EVENT,
 	MLXSW_REG_HTGT_TRAP_GROUP_SP_IPV6_MLD,
 	MLXSW_REG_HTGT_TRAP_GROUP_SP_IPV6_ND,
+	MLXSW_REG_HTGT_TRAP_GROUP_SP_LBERROR,
 };
 
 /* reg_htgt_trap_group

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

@@ -3639,7 +3639,7 @@ static const struct mlxsw_listener mlxsw_sp_listener[] = {
 	/* L3 traps */
 	MLXSW_SP_RXL_MARK(MTUERROR, TRAP_TO_CPU, ROUTER_EXP, false),
 	MLXSW_SP_RXL_MARK(TTLERROR, TRAP_TO_CPU, ROUTER_EXP, false),
-	MLXSW_SP_RXL_MARK(LBERROR, TRAP_TO_CPU, ROUTER_EXP, false),
+	MLXSW_SP_RXL_L3_MARK(LBERROR, MIRROR_TO_CPU, LBERROR, false),
 	MLXSW_SP_RXL_MARK(IP2ME, TRAP_TO_CPU, IP2ME, false),
 	MLXSW_SP_RXL_MARK(IPV6_UNSPECIFIED_ADDRESS, TRAP_TO_CPU, ROUTER_EXP,
 			  false),
@@ -3713,6 +3713,7 @@ static int mlxsw_sp_cpu_policers_set(struct mlxsw_core *mlxsw_core)
 		case MLXSW_REG_HTGT_TRAP_GROUP_SP_OSPF:
 		case MLXSW_REG_HTGT_TRAP_GROUP_SP_PIM:
 		case MLXSW_REG_HTGT_TRAP_GROUP_SP_RPF:
+		case MLXSW_REG_HTGT_TRAP_GROUP_SP_LBERROR:
 			rate = 128;
 			burst_size = 7;
 			break;
@@ -3798,6 +3799,7 @@ static int mlxsw_sp_trap_groups_set(struct mlxsw_core *mlxsw_core)
 		case MLXSW_REG_HTGT_TRAP_GROUP_SP_ROUTER_EXP:
 		case MLXSW_REG_HTGT_TRAP_GROUP_SP_REMOTE_ROUTE:
 		case MLXSW_REG_HTGT_TRAP_GROUP_SP_MULTICAST:
+		case MLXSW_REG_HTGT_TRAP_GROUP_SP_LBERROR:
 			priority = 1;
 			tc = 1;
 			break;