[PATCH v5 net-next 00/15] net: bridge: Multiple Spanning Trees

Tobias Waldekranz
2022-03-16T15:09:13Z

The bridge has had per-VLAN STP support for a while now, since:

https://lore.kernel.org/netdev/20200124114022.10883-1-nikolay@cumulusnetworks.com/

The current implementation has some problems:

- The mapping from VLAN to STP state is fixed as 1:1, i.e. each VLAN
is managed independently. This is awkward from an MSTP (802.1Q-2018,
Clause 13.5) point of view, where the model is that multiple VLANs
are grouped into MST instances.

Because of the way that the standard is written, presumably, this is
also reflected in hardware implementations. It is not uncommon for a
switch to support the full 4k range of VIDs, but that the pool of
MST instances is much smaller. Some examples:

Marvell LinkStreet (mv88e6xxx): 4k VLANs, but only 64 MSTIs
Marvell Prestera: 4k VLANs, but only 128 MSTIs
Microchip SparX-5i: 4k VLANs, but only 128 MSTIs

- By default, the feature is enabled, and there is no way to disable
it. This makes it hard to add offloading in a backwards compatible
way, since any underlying switchdevs have no way to refuse the
function if the hardware does not support it

- The port-global STP state has precedence over per-VLAN states. In
MSTP, as far as I understand it, all VLANs will use the common
spanning tree (CST) by default - through traffic engineering you can
then optimize your network to group subsets of VLANs to use
different trees (MSTI). To my understanding, the way this is
typically managed in silicon is roughly:

Incoming packet:
.----.----.--------------.----.-------------
| DA | SA | 802.1Q VID=X | ET | Payload ...
'----'----'--------------'----'-------------
|
'->|\ .----------------------------.
| +--> | VID | Members | ... | MSTI |
PVID -->|/ |-----|---------|-----|------|
| 1 | 0001001 | ... | 0 |
| 2 | 0001010 | ... | 10 |
| 3 | 0001100 | ... | 10 |
'----------------------------'
|
.-----------------------------'
| .------------------------.
'->| MSTI | Fwding | Lrning |
|------|--------|--------|
| 0 | 111110 | 111110 |
| 10 | 110111 | 110111 |
'------------------------'

What this is trying to show is that the STP state (whether MSTP is
used, or ye olde STP) is always accessed via the VLAN table. If STP
is running, all MSTI pointers in that table will reference the same
index in the STP stable - if MSTP is running, some VLANs may point
to other trees (like in this example).

The fact that in the Linux bridge, the global state (think: index 0
in most hardware implementations) is supposed to override the
per-VLAN state, is very awkward to offload. In effect, this means
that when the global state changes to blocking, drivers will have to
iterate over all MSTIs in use, and alter them all to match. This
also means that you have to cache whether the hardware state is
currently tracking the global state or the per-VLAN state. In the
first case, you also have to cache the per-VLAN state so that you
can restore it if the global state transitions back to forwarding.

This series adds a new mst_enable bridge setting (as suggested by Nik)
that can only be changed when no VLANs are configured on the
bridge. Enabling this mode has the following effect:

- The port-global STP state is used to represent the CST (Common
Spanning Tree) (1/15)

- Ingress STP filtering is deferred until the frame's VLAN has been
resolved (1/15)

- The preexisting per-VLAN states can no longer be controlled directly
(1/15). They are instead placed under the MST module's control,
which is managed using a new netlink interface (described in 3/15)

- VLANs can br mapped to MSTIs in an arbitrary M:N fashion, using a
new global VLAN option (2/15)

Switchdev notifications are added so that a driver can track:
- MST enabled state
- VID to MSTI mappings
- MST port states

An offloading implementation is this provided for mv88e6xxx.

A proposal for the corresponding iproute2 interface is available here:

https://github.com/wkz/iproute2/tree/mst

v4 -> v5:
Bridge:
- Fix build error in intermediate commit (Jakub)
- Use rcu safe list iterator in br_mst_info_size (Nik)
- Propagate any errors back to the caller when changing an MST state
(Vladimir)
DSA:
- Boolean algebra workshop (Vladimir, feat. De Morgan)
- Only flush FDBs on ports when transitioning from
forwarding/learning to listening/blocking/disabled (Vladimir)

v3 -> v4:
Bridge:
- Constify arguments where possible (Nik)
- Use non-atomic bitmap operators (Nik)
- Rename br_mst_parse -> br_mst_process (Nik)
- Account for the dynamic size of generated MST netlink data (Nik)
- Provide proper error reporting on invalid input (Nik)
- Export bridge helpers under GPL (Nik)
- Fix build when bridge VLAN filtering is compiled out (Intel bot)
- Allocate VLAN bitmaps on the stack (Vladimir)
DSA:
- Propagate MST state change errors back to the bridge layer
(Vladimir)
- Fix issue with software fallback (Vladimir)
- Ignore FDB events on software bridged ports
mv88e6xxx:
- Use non-atomic bitmap operators (Vladimir)
- Restore refcount in error path (Vladimir)

v2 -> v3:
Bridge:
- Use new boolopt API to enable/disable the MST mode (Nik)
- Mark br_mst_vlan_set_state as static (Vladimir)
- Avoid updates/notifications on repeated VLAN to MSTI mapping
configurations (Vladimir)
- Configure MSTI states via the existing RTM_GET/SETLINK interface
(Roopa)
- Refactor switchdev replay logic (Vladimir)
- Send switchdev notifications when enabling/disabling MST
(Vladimir)
DSA:
- Align VLAN MSTI callback with existing APIs (Vladimir)
- Only flush entries in the affected VLANs when changing an MST
state (Vladimir)
- Refuse offloading, unless all required ops are implemented
(Vladimir)
mv88e6xxx:
- Always keep the driver's MST state in sync with hardware
(Vladimir)
- Fix SID leaks (Vladimir)
- Only flush entries in the affected VLANs when changing an MST
state (Vladimir)

v1 (RFC) -> v2:
- Add a separate MST mode that is distinct from the exiting per-VLAN
state functionality
- Control MSTI states explicitly, rather than via an associated VLAN

Tobias Waldekranz (15):
net: bridge: mst: Multiple Spanning Tree (MST) mode
net: bridge: mst: Allow changing a VLAN's MSTI
net: bridge: mst: Support setting and reporting MST port states
net: bridge: mst: Notify switchdev drivers of MST mode changes
net: bridge: mst: Notify switchdev drivers of VLAN MSTI migrations
net: bridge: mst: Notify switchdev drivers of MST state changes
net: bridge: mst: Add helper to map an MSTI to a VID set
net: bridge: mst: Add helper to check if MST is enabled
net: bridge: mst: Add helper to query a port's MST state
net: dsa: Validate hardware support for MST
net: dsa: Pass VLAN MSTI migration notifications to driver
net: dsa: Handle MST state changes
net: dsa: mv88e6xxx: Disentangle STU from VTU
net: dsa: mv88e6xxx: Export STU as devlink region
net: dsa: mv88e6xxx: MST Offloading

drivers/net/dsa/mv88e6xxx/chip.c | 304 +++++++++++++++++++-
drivers/net/dsa/mv88e6xxx/chip.h | 38 +++
drivers/net/dsa/mv88e6xxx/devlink.c | 94 +++++++
drivers/net/dsa/mv88e6xxx/global1.h | 10 +
drivers/net/dsa/mv88e6xxx/global1_vtu.c | 311 ++++++++++++---------
include/linux/if_bridge.h | 19 ++
include/net/dsa.h | 6 +
include/net/switchdev.h | 16 ++
include/uapi/linux/if_bridge.h | 18 ++
include/uapi/linux/rtnetlink.h | 1 +
net/bridge/Makefile | 2 +-
net/bridge/br.c | 5 +
net/bridge/br_input.c | 17 +-
net/bridge/br_mst.c | 357 ++++++++++++++++++++++++
net/bridge/br_netlink.c | 44 ++-
net/bridge/br_private.h | 61 ++++
net/bridge/br_stp.c | 6 +
net/bridge/br_switchdev.c | 46 +++
net/bridge/br_vlan.c | 20 +-
net/bridge/br_vlan_options.c | 20 ++
net/dsa/dsa_priv.h | 7 +
net/dsa/port.c | 113 +++++++-
net/dsa/slave.c | 18 ++
23 files changed, 1381 insertions(+), 152 deletions(-)
create mode 100644 net/bridge/br_mst.c

--
2.25.1