From: Vladimir Oltean vladimir.oltean@nxp.com
[ Upstream commit 927cdea5d2095287ddd5246e5aa68eb5d68db2be ]
There is a structural problem in switchdev, where the flag bits in struct switchdev_notifier_fdb_info (added_by_user, is_local etc) only represent a simplified / denatured view of what's in struct net_bridge_fdb_entry :: flags (BR_FDB_ADDED_BY_USER, BR_FDB_LOCAL etc). Each time we want to pass more information about struct net_bridge_fdb_entry :: flags to struct switchdev_notifier_fdb_info (here, BR_FDB_STATIC), we find that FDB entries were already notified to switchdev with no regard to this flag, and thus, switchdev drivers had no indication whether the notified entries were static or not.
For example, this command:
ip link add br0 type bridge && ip link set swp0 master br0 bridge fdb add dev swp0 00:01:02:03:04:05 master dynamic
has never worked as intended with switchdev. It causes a struct net_bridge_fdb_entry to be passed to br_switchdev_fdb_notify() which has a single flag set: BR_FDB_ADDED_BY_USER.
This is further passed to the switchdev notifier chain, where interested drivers have no choice but to assume this is a static (does not age) and sticky (does not migrate) FDB entry. So currently, all drivers offload it to hardware as such, as can be seen below ("offload" is set).
bridge fdb get 00:01:02:03:04:05 dev swp0 master 00:01:02:03:04:05 dev swp0 offload master br0
The software FDB entry expires $ageing_time centiseconds after the kernel last sees a packet with this MAC SA, and the bridge notifies its deletion as well, so it eventually disappears from hardware too.
This is a problem, because it is actually desirable to start offloading "master dynamic" FDB entries correctly - they should expire $ageing_time centiseconds after the *hardware* port last sees a packet with this MAC SA - and this is how the current incorrect behavior was discovered. With an offloaded data plane, it can be expected that software only sees exception path packets, so an otherwise active dynamic FDB entry would be aged out by software sooner than it should.
With the change in place, these FDB entries are no longer offloaded:
bridge fdb get 00:01:02:03:04:05 dev swp0 master 00:01:02:03:04:05 dev swp0 master br0
and this also constitutes a better way (assuming a backport to stable kernels) for user space to determine whether the kernel has the capability of doing something sane with these or not.
As opposed to "master dynamic" FDB entries, on the current behavior of which no one currently depends on (which can be deduced from the lack of kselftests), Ido Schimmel explains that entries with the "extern_learn" flag (BR_FDB_ADDED_BY_EXT_LEARN) should still be notified to switchdev, since the spectrum driver listens to them (and this is kind of okay, because although they are treated identically to "static", they are expected to not age, and to roam).
Fixes: 6b26b51b1d13 ("net: bridge: Add support for notifying devices about FDB add/del") Link: https://lore.kernel.org/netdev/20230327115206.jk5q5l753aoelwus@skbuf/ Signed-off-by: Vladimir Oltean vladimir.oltean@nxp.com Reviewed-by: Jesse Brandeburg jesse.brandeburg@intel.com Reviewed-by: Ido Schimmel idosch@nvidia.com Tested-by: Ido Schimmel idosch@nvidia.com Link: https://lore.kernel.org/r/20230418155902.898627-1-vladimir.oltean@nxp.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/bridge/br_switchdev.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/net/bridge/br_switchdev.c b/net/bridge/br_switchdev.c index 8f3d76c751dd0..4b3982c368b35 100644 --- a/net/bridge/br_switchdev.c +++ b/net/bridge/br_switchdev.c @@ -146,6 +146,17 @@ br_switchdev_fdb_notify(struct net_bridge *br, { struct switchdev_notifier_fdb_info item;
+ /* Entries with these flags were created using ndm_state == NUD_REACHABLE, + * ndm_flags == NTF_MASTER( | NTF_STICKY), ext_flags == 0 by something + * equivalent to 'bridge fdb add ... master dynamic (sticky)'. + * Drivers don't know how to deal with these, so don't notify them to + * avoid confusing them. + */ + if (test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags) && + !test_bit(BR_FDB_STATIC, &fdb->flags) && + !test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) + return; + br_switchdev_fdb_populate(br, &item, fdb, NULL);
switch (type) {