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docs: net: dsa: add a section for address databases
The given definition for what VID 0 represents in the current
port_fdb_add and port_mdb_add is blatantly wrong. Delete it and explain
the concepts surrounding DSA's understanding of FDB isolation.
Fixes: c26933639b ("net: dsa: request drivers to perform FDB isolation")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Vladimir Oltean
David S. Miller
parent
7f75d3dd4f
commit
4e9d9bb6df
@ -727,6 +727,136 @@ Power management
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``BR_STATE_DISABLED`` and propagating changes to the hardware if this port is
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disabled while being a bridge member
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Address databases
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-----------------
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Switching hardware is expected to have a table for FDB entries, however not all
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of them are active at the same time. An address database is the subset (partition)
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of FDB entries that is active (can be matched by address learning on RX, or FDB
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lookup on TX) depending on the state of the port. An address database may
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occasionally be called "FID" (Filtering ID) in this document, although the
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underlying implementation may choose whatever is available to the hardware.
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For example, all ports that belong to a VLAN-unaware bridge (which is
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*currently* VLAN-unaware) are expected to learn source addresses in the
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database associated by the driver with that bridge (and not with other
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VLAN-unaware bridges). During forwarding and FDB lookup, a packet received on a
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VLAN-unaware bridge port should be able to find a VLAN-unaware FDB entry having
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the same MAC DA as the packet, which is present on another port member of the
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same bridge. At the same time, the FDB lookup process must be able to not find
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an FDB entry having the same MAC DA as the packet, if that entry points towards
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a port which is a member of a different VLAN-unaware bridge (and is therefore
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associated with a different address database).
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Similarly, each VLAN of each offloaded VLAN-aware bridge should have an
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associated address database, which is shared by all ports which are members of
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that VLAN, but not shared by ports belonging to different bridges that are
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members of the same VID.
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In this context, a VLAN-unaware database means that all packets are expected to
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match on it irrespective of VLAN ID (only MAC address lookup), whereas a
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VLAN-aware database means that packets are supposed to match based on the VLAN
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ID from the classified 802.1Q header (or the pvid if untagged).
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At the bridge layer, VLAN-unaware FDB entries have the special VID value of 0,
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whereas VLAN-aware FDB entries have non-zero VID values. Note that a
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VLAN-unaware bridge may have VLAN-aware (non-zero VID) FDB entries, and a
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VLAN-aware bridge may have VLAN-unaware FDB entries. As in hardware, the
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software bridge keeps separate address databases, and offloads to hardware the
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FDB entries belonging to these databases, through switchdev, asynchronously
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relative to the moment when the databases become active or inactive.
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When a user port operates in standalone mode, its driver should configure it to
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use a separate database called a port private database. This is different from
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the databases described above, and should impede operation as standalone port
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(packet in, packet out to the CPU port) as little as possible. For example,
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on ingress, it should not attempt to learn the MAC SA of ingress traffic, since
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learning is a bridging layer service and this is a standalone port, therefore
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it would consume useless space. With no address learning, the port private
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database should be empty in a naive implementation, and in this case, all
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received packets should be trivially flooded to the CPU port.
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DSA (cascade) and CPU ports are also called "shared" ports because they service
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multiple address databases, and the database that a packet should be associated
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to is usually embedded in the DSA tag. This means that the CPU port may
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simultaneously transport packets coming from a standalone port (which were
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classified by hardware in one address database), and from a bridge port (which
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were classified to a different address database).
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Switch drivers which satisfy certain criteria are able to optimize the naive
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configuration by removing the CPU port from the flooding domain of the switch,
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and just program the hardware with FDB entries pointing towards the CPU port
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for which it is known that software is interested in those MAC addresses.
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Packets which do not match a known FDB entry will not be delivered to the CPU,
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which will save CPU cycles required for creating an skb just to drop it.
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DSA is able to perform host address filtering for the following kinds of
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addresses:
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- Primary unicast MAC addresses of ports (``dev->dev_addr``). These are
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associated with the port private database of the respective user port,
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and the driver is notified to install them through ``port_fdb_add`` towards
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the CPU port.
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- Secondary unicast and multicast MAC addresses of ports (addresses added
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through ``dev_uc_add()`` and ``dev_mc_add()``). These are also associated
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with the port private database of the respective user port.
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- Local/permanent bridge FDB entries (``BR_FDB_LOCAL``). These are the MAC
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addresses of the bridge ports, for which packets must be terminated locally
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and not forwarded. They are associated with the address database for that
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bridge.
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- Static bridge FDB entries installed towards foreign (non-DSA) interfaces
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present in the same bridge as some DSA switch ports. These are also
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associated with the address database for that bridge.
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- Dynamically learned FDB entries on foreign interfaces present in the same
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bridge as some DSA switch ports, only if ``ds->assisted_learning_on_cpu_port``
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is set to true by the driver. These are associated with the address database
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for that bridge.
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For various operations detailed below, DSA provides a ``dsa_db`` structure
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which can be of the following types:
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- ``DSA_DB_PORT``: the FDB (or MDB) entry to be installed or deleted belongs to
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the port private database of user port ``db->dp``.
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- ``DSA_DB_BRIDGE``: the entry belongs to one of the address databases of bridge
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``db->bridge``. Separation between the VLAN-unaware database and the per-VID
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databases of this bridge is expected to be done by the driver.
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- ``DSA_DB_LAG``: the entry belongs to the address database of LAG ``db->lag``.
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Note: ``DSA_DB_LAG`` is currently unused and may be removed in the future.
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The drivers which act upon the ``dsa_db`` argument in ``port_fdb_add``,
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``port_mdb_add`` etc should declare ``ds->fdb_isolation`` as true.
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DSA associates each offloaded bridge and each offloaded LAG with a one-based ID
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(``struct dsa_bridge :: num``, ``struct dsa_lag :: id``) for the purposes of
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refcounting addresses on shared ports. Drivers may piggyback on DSA's numbering
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scheme (the ID is readable through ``db->bridge.num`` and ``db->lag.id`` or may
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implement their own.
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Only the drivers which declare support for FDB isolation are notified of FDB
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entries on the CPU port belonging to ``DSA_DB_PORT`` databases.
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For compatibility/legacy reasons, ``DSA_DB_BRIDGE`` addresses are notified to
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drivers even if they do not support FDB isolation. However, ``db->bridge.num``
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and ``db->lag.id`` are always set to 0 in that case (to denote the lack of
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isolation, for refcounting purposes).
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Note that it is not mandatory for a switch driver to implement physically
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separate address databases for each standalone user port. Since FDB entries in
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the port private databases will always point to the CPU port, there is no risk
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for incorrect forwarding decisions. In this case, all standalone ports may
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share the same database, but the reference counting of host-filtered addresses
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(not deleting the FDB entry for a port's MAC address if it's still in use by
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another port) becomes the responsibility of the driver, because DSA is unaware
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that the port databases are in fact shared. This can be achieved by calling
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``dsa_fdb_present_in_other_db()`` and ``dsa_mdb_present_in_other_db()``.
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The down side is that the RX filtering lists of each user port are in fact
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shared, which means that user port A may accept a packet with a MAC DA it
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shouldn't have, only because that MAC address was in the RX filtering list of
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user port B. These packets will still be dropped in software, however.
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Bridge layer
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------------
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@ -835,9 +965,6 @@ Bridge VLAN filtering
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function should return ``-EOPNOTSUPP`` to inform the bridge code to fallback to
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a software implementation.
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.. note:: VLAN ID 0 corresponds to the port private database, which, in the context
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of DSA, would be its port-based VLAN, used by the associated bridge device.
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- ``port_fdb_del``: bridge layer function invoked when the bridge wants to remove a
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Forwarding Database entry, the switch hardware should be programmed to delete
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the specified MAC address from the specified VLAN ID if it was mapped into
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@ -854,9 +981,6 @@ Bridge VLAN filtering
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specified address in the specified VLAN ID in the forwarding database
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associated with this VLAN ID.
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.. note:: VLAN ID 0 corresponds to the port private database, which, in the context
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of DSA, would be its port-based VLAN, used by the associated bridge device.
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- ``port_mdb_del``: bridge layer function invoked when the bridge wants to remove a
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multicast database entry, the switch hardware should be programmed to delete
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the specified MAC address from the specified VLAN ID if it was mapped into
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