It is possible to add a filter that redirects traffic from the ingress
of a bridge port that is locked (i.e., performs security / SMAC lookup)
and has learning enabled. For example:

 # ip link add name br0 type bridge
 # ip link set dev swp1 master br0
 # bridge link set dev swp1 learning on locked on mab on
 # tc qdisc add dev swp1 clsact
 # tc filter add dev swp1 ingress pref 1 proto ip flower skip_sw src_ip 192.0.2.1 action mirred egress redirect dev swp2

In the kernel's Rx path, this filter is evaluated before the Rx handler
of the bridge, which means that redirected traffic should not be
affected by bridge port configuration such as learning.

However, the hardware data path is a bit different and the redirect
action (FORWARDING_ACTION in hardware) merely attaches a pointer to the
packet, which is later used by the L2 lookup stage to understand how to
forward the packet. Between both stages - ingress ACL and L2 lookup -
learning and security lookup are performed, which means that redirected
traffic is affected by bridge port configuration, unlike in the kernel's
data path.

The learning discrepancy was handled in commit 577fa14d ("mlxsw:
spectrum: Do not process learned records with a dummy FID") by simply
ignoring learning notifications generated by the redirected traffic. A
similar solution is not possible for the security / SMAC lookup since
- unlike learning - the CPU is not involved and packets that failed the
lookup are dropped by the device.

Instead, solve this by prepending the ignore action to the redirect
action and use it to instruct the device to disable both learning and
the security / SMAC lookup for redirected traffic.
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>