Merge branch 'dsa-rx-filtering'

Vladimir Oltean says:

====================
RX filtering in DSA

This is my fourth stab (identical to the third one except sent as
non-RFC) at creating a list of unicast and multicast addresses that the
DSA CPU ports must trap. I am reusing a lot of Tobias's work which he
submitted here:
https://patchwork.kernel.org/project/netdevbpf/cover/20210116012515.3152-1-tobias@waldekranz.com/

My additions to Tobias' work come in the form of taking some care that
additions and removals of host addresses are properly balanced, so that
we can do reference counting on them for cross-chip setups and multiple
bridges spanning the same switch (I am working on an NXP board where
both are real requirements).

During the last attempted submission of multiple CPU ports for DSA:
https://patchwork.kernel.org/project/netdevbpf/cover/20210410133454.4768-1-ansuelsmth@gmail.com/

it became clear that the concept of multiple CPU ports would not be
compatible with the idea of address learning on those CPU ports (when
those CPU ports are statically assigned to user ports, not in a LAG)
unless the switch supports complete FDB isolation, which most switches
do not. So DSA needs to manage in software all addresses that are
installed on the CPU port(s), which is what this patch set does.

Compared to all earlier attempts, this series does not fiddle with how
DSA operates the ports in standalone mode at all, just when bridged.
We need to sort that out properly, then any optimization that comes in
standalone mode (i.e. IFF_UNICAST_FLT) can come later.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 68 insertions, 0 deletions

diff --git a/Documentation/networking/dsa/configuration.rst b/Documentation/networking/dsa/configuration.rst
index 774f0e76c746..2b08f1a772d3 100644
--- a/Documentation/networking/dsa/configuration.rst
+++ b/Documentation/networking/dsa/configuration.rst
@@ -292,3 +292,71 @@ configuration.
 
     # bring up the bridge devices
     ip link set br0 up
+
+Forwarding database (FDB) management
+------------------------------------
+
+The existing DSA switches do not have the necessary hardware support to keep
+the software FDB of the bridge in sync with the hardware tables, so the two
+tables are managed separately (``bridge fdb show`` queries both, and depending
+on whether the ``self`` or ``master`` flags are being used, a ``bridge fdb
+add`` or ``bridge fdb del`` command acts upon entries from one or both tables).
+
+Up until kernel v4.14, DSA only supported user space management of bridge FDB
+entries using the bridge bypass operations (which do not update the software
+FDB, just the hardware one) using the ``self`` flag (which is optional and can
+be omitted).
+
+  .. code-block:: sh
+
+    bridge fdb add dev swp0 00:01:02:03:04:05 self static
+    # or shorthand
+    bridge fdb add dev swp0 00:01:02:03:04:05 static
+
+Due to a bug, the bridge bypass FDB implementation provided by DSA did not
+distinguish between ``static`` and ``local`` FDB entries (``static`` are meant
+to be forwarded, while ``local`` are meant to be locally terminated, i.e. sent
+to the host port). Instead, all FDB entries with the ``self`` flag (implicit or
+explicit) are treated by DSA as ``static`` even if they are ``local``.
+
+  .. code-block:: sh
+
+    # This command:
+    bridge fdb add dev swp0 00:01:02:03:04:05 static
+    # behaves the same for DSA as this command:
+    bridge fdb add dev swp0 00:01:02:03:04:05 local
+    # or shorthand, because the 'local' flag is implicit if 'static' is not
+    # specified, it also behaves the same as:
+    bridge fdb add dev swp0 00:01:02:03:04:05
+
+The last command is an incorrect way of adding a static bridge FDB entry to a
+DSA switch using the bridge bypass operations, and works by mistake. Other
+drivers will treat an FDB entry added by the same command as ``local`` and as
+such, will not forward it, as opposed to DSA.
+
+Between kernel v4.14 and v5.14, DSA has supported in parallel two modes of
+adding a bridge FDB entry to the switch: the bridge bypass discussed above, as
+well as a new mode using the ``master`` flag which installs FDB entries in the
+software bridge too.
+
+  .. code-block:: sh
+
+    bridge fdb add dev swp0 00:01:02:03:04:05 master static
+
+Since kernel v5.14, DSA has gained stronger integration with the bridge's
+software FDB, and the support for its bridge bypass FDB implementation (using
+the ``self`` flag) has been removed. This results in the following changes:
+
+  .. code-block:: sh
+
+    # This is the only valid way of adding an FDB entry that is supported,
+    # compatible with v4.14 kernels and later:
+    bridge fdb add dev swp0 00:01:02:03:04:05 master static
+    # This command is no longer buggy and the entry is properly treated as
+    # 'local' instead of being forwarded:
+    bridge fdb add dev swp0 00:01:02:03:04:05
+    # This command no longer installs a static FDB entry to hardware:
+    bridge fdb add dev swp0 00:01:02:03:04:05 static
+
+Script writers are therefore encouraged to use the ``master static`` set of
+flags when working with bridge FDB entries on DSA switch interfaces.