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linux-next/net/bridge
Vladimir Oltean 90dc8fd360 net: bridge: notify switchdev of disappearance of old FDB entry upon migration
Currently the bridge emits atomic switchdev notifications for
dynamically learnt FDB entries. Monitoring these notifications works
wonders for switchdev drivers that want to keep their hardware FDB in
sync with the bridge's FDB.

For example station A wants to talk to station B in the diagram below,
and we are concerned with the behavior of the bridge on the DUT device:

                   DUT
 +-------------------------------------+
 |                 br0                 |
 | +------+ +------+ +------+ +------+ |
 | |      | |      | |      | |      | |
 | | swp0 | | swp1 | | swp2 | | eth0 | |
 +-------------------------------------+
      |        |                  |
  Station A    |                  |
               |                  |
         +--+------+--+    +--+------+--+
         |  |      |  |    |  |      |  |
         |  | swp0 |  |    |  | swp0 |  |
 Another |  +------+  |    |  +------+  | Another
  switch |     br0    |    |     br0    | switch
         |  +------+  |    |  +------+  |
         |  |      |  |    |  |      |  |
         |  | swp1 |  |    |  | swp1 |  |
         +--+------+--+    +--+------+--+
                                  |
                              Station B

Interfaces swp0, swp1, swp2 are handled by a switchdev driver that has
the following property: frames injected from its control interface bypass
the internal address analyzer logic, and therefore, this hardware does
not learn from the source address of packets transmitted by the network
stack through it. So, since bridging between eth0 (where Station B is
attached) and swp0 (where Station A is attached) is done in software,
the switchdev hardware will never learn the source address of Station B.
So the traffic towards that destination will be treated as unknown, i.e.
flooded.

This is where the bridge notifications come in handy. When br0 on the
DUT sees frames with Station B's MAC address on eth0, the switchdev
driver gets these notifications and can install a rule to send frames
towards Station B's address that are incoming from swp0, swp1, swp2,
only towards the control interface. This is all switchdev driver private
business, which the notification makes possible.

All is fine until someone unplugs Station B's cable and moves it to the
other switch:

                   DUT
 +-------------------------------------+
 |                 br0                 |
 | +------+ +------+ +------+ +------+ |
 | |      | |      | |      | |      | |
 | | swp0 | | swp1 | | swp2 | | eth0 | |
 +-------------------------------------+
      |        |                  |
  Station A    |                  |
               |                  |
         +--+------+--+    +--+------+--+
         |  |      |  |    |  |      |  |
         |  | swp0 |  |    |  | swp0 |  |
 Another |  +------+  |    |  +------+  | Another
  switch |     br0    |    |     br0    | switch
         |  +------+  |    |  +------+  |
         |  |      |  |    |  |      |  |
         |  | swp1 |  |    |  | swp1 |  |
         +--+------+--+    +--+------+--+
               |
           Station B

Luckily for the use cases we care about, Station B is noisy enough that
the DUT hears it (on swp1 this time). swp1 receives the frames and
delivers them to the bridge, who enters the unlikely path in br_fdb_update
of updating an existing entry. It moves the entry in the software bridge
to swp1 and emits an addition notification towards that.

As far as the switchdev driver is concerned, all that it needs to ensure
is that traffic between Station A and Station B is not forever broken.
If it does nothing, then the stale rule to send frames for Station B
towards the control interface remains in place. But Station B is no
longer reachable via the control interface, but via a port that can
offload the bridge port learning attribute. It's just that the port is
prevented from learning this address, since the rule overrides FDB
updates. So the rule needs to go. The question is via what mechanism.

It sure would be possible for this switchdev driver to keep track of all
addresses which are sent to the control interface, and then also listen
for bridge notifier events on its own ports, searching for the ones that
have a MAC address which was previously sent to the control interface.
But this is cumbersome and inefficient. Instead, with one small change,
the bridge could notify of the address deletion from the old port, in a
symmetrical manner with how it did for the insertion. Then the switchdev
driver would not be required to monitor learn/forget events for its own
ports. It could just delete the rule towards the control interface upon
bridge entry migration. This would make hardware address learning be
possible again. Then it would take a few more packets until the hardware
and software FDB would be in sync again.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2021-01-07 15:34:45 -08:00
..
netfilter netfilter: nft_reject_bridge: fix build errors due to code movement 2020-11-22 13:44:51 +01:00
br_arp_nd_proxy.c net: core: introduce struct netdev_nested_priv for nested interface infrastructure 2020-09-28 15:00:15 -07:00
br_cfm_netlink.c bridge: cfm: Netlink Notifications. 2020-10-29 18:39:44 -07:00
br_cfm.c bridge: cfm: Netlink Notifications. 2020-10-29 18:39:44 -07:00
br_device.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-12-11 22:29:38 -08:00
br_fdb.c net: bridge: notify switchdev of disappearance of old FDB entry upon migration 2021-01-07 15:34:45 -08:00
br_forward.c net: bridge: mcast: when forwarding handle filter mode and blocked flag 2020-09-23 13:24:35 -07:00
br_if.c bridge: cfm: Kernel space implementation of CFM. MEP create/delete. 2020-10-29 18:39:43 -07:00
br_input.c net: bridge: switch to net core statistics counters handling 2020-11-21 14:40:50 -08:00
br_ioctl.c net: bridge: delete duplicated words 2020-09-18 14:12:43 -07:00
br_mdb.c net: bridge: explicitly convert between mdb entry state and port group flags 2020-10-30 17:58:16 -07:00
br_mrp_netlink.c bridge: mrp: Use hlist_head instead of list_head for mrp 2020-11-09 16:42:12 -08:00
br_mrp_switchdev.c bridge: switchdev: mrp: Extend MRP API for switchdev for MRP Interconnect 2020-07-14 13:46:43 -07:00
br_mrp.c bridge: mrp: Implement LC mode for MRP 2020-11-25 13:33:35 -08:00
br_multicast.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-12-11 22:29:38 -08:00
br_netfilter_hooks.c netfilter: bridge: reset skb->pkt_type after NF_INET_POST_ROUTING traversal 2020-11-28 11:46:51 -08:00
br_netfilter_ipv6.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2019-06-25 01:32:59 +02:00
br_netlink_tunnel.c net: bridge: notify on vlan tunnel changes done via the old api 2020-07-12 15:18:24 -07:00
br_netlink.c net: bridge: replace struct br_vlan_stats with pcpu_sw_netstats 2020-11-18 17:23:16 -08:00
br_nf_core.c net: add bool confirm_neigh parameter for dst_ops.update_pmtu 2019-12-24 22:28:54 -08:00
br_private_cfm.h bridge: cfm: Kernel space implementation of CFM. CCM frame RX added. 2020-10-29 18:39:43 -07:00
br_private_mrp.h bridge: mrp: Use hlist_head instead of list_head for mrp 2020-11-09 16:42:12 -08:00
br_private_stp.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
br_private_tunnel.h net: bridge: vlan options: add support for tunnel mapping set/del 2020-03-17 22:47:12 -07:00
br_private.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-12-11 22:29:38 -08:00
br_stp_bpdu.c net: bridge: add STP xstats 2019-12-14 20:02:36 -08:00
br_stp_if.c net: remove newlines in NL_SET_ERR_MSG_MOD 2020-05-07 17:56:14 -07:00
br_stp_timer.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
br_stp.c net: bridge: Add checks for enabling the STP. 2020-04-27 11:40:25 -07:00
br_switchdev.c net: bridge: fdb: convert offloaded to use bitops 2019-10-29 18:12:49 -07:00
br_sysfs_br.c net: bridge: Add checks for enabling the STP. 2020-04-27 11:40:25 -07:00
br_sysfs_if.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
br_vlan_options.c net: bridge: vlan options: move the tunnel command to the nested attribute 2020-03-20 08:52:20 -07:00
br_vlan_tunnel.c net: bridge: vlan tunnel: constify bridge and port arguments 2020-03-17 22:47:12 -07:00
br_vlan.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-12-11 22:29:38 -08:00
br.c net: bridge: Fix a warning when del bridge sysfs 2020-12-14 18:27:49 -08:00
Kconfig bridge: cfm: Add BRIDGE_CFM to Kconfig. 2020-10-29 18:39:43 -07:00
Makefile bridge: cfm: Netlink SET configuration Interface. 2020-10-29 18:39:43 -07:00