Linux Ethernet Bridging - Dec 2020 - [Bridge] [PATCH v3 net-next 0/7] Offload software learnt bridge addresses to DSA

This series tries to make DSA behave a bit more sanely when bridged with
"foreign" (non-DSA) interfaces and source address learning is not
supported on the hardware CPU port (which would make things work more
seamlessly without software intervention). When a station A connected to
a DSA switch port needs to talk to another station B connected to a
non-DSA port through the Linux bridge, DSA must explicitly add a route
for station B towards its CPU port.

Initial RFC was posted here:
https://patchwork.ozlabs.org/project/netdev/cover/20201108131953.2462644-1-olteanv
at gmail.com/

v2 was posted here:
https://patchwork.kernel.org/project/netdevbpf/cover/20201213024018.772586-1-vladimir.oltean
at nxp.com/

Vladimir Oltean (7):
  net: bridge: notify switchdev of disappearance of old FDB entry upon
    migration
  net: dsa: be louder when a non-legacy FDB operation fails
  net: dsa: don't use switchdev_notifier_fdb_info in
    dsa_switchdev_event_work
  net: dsa: move switchdev event implementation under the same
    switch/case statement
  net: dsa: exit early in dsa_slave_switchdev_event if we can't program
    the FDB
  net: dsa: listen for SWITCHDEV_{FDB,DEL}_ADD_TO_DEVICE on foreign
    bridge neighbors
  net: dsa: ocelot: request DSA to fix up lack of address learning on
    CPU port

 drivers/net/dsa/ocelot/felix.c |   1 +
 include/net/dsa.h              |   5 +
 net/bridge/br_fdb.c            |   1 +
 net/dsa/dsa_priv.h             |  12 +++
 net/dsa/slave.c                | 174 +++++++++++++++++++++------------
 5 files changed, 130 insertions(+), 63 deletions(-)

-- 
2.25.1

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 at nxp.com>
Acked-by: Nikolay Aleksandrov <nikolay at nvidia.com>
---
Changes in v3:
None.

Changes in v2:
Patch is new.

 net/bridge/br_fdb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index 32ac8343b0ba..b7490237f3fc 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -602,6 +602,7 @@ void br_fdb_update(struct net_bridge *br, struct
net_bridge_port *source,
 			/* fastpath: update of existing entry */
 			if (unlikely(source != fdb->dst &&
 				     !test_bit(BR_FDB_STICKY, &fdb->flags))) {
+				br_switchdev_fdb_notify(fdb, RTM_DELNEIGH);
 				fdb->dst = source;
 				fdb_modified = true;
 				/* Take over HW learned entry */
-- 
2.25.1

The dev_close() call was added in commit c9eb3e0f8701 ("net: dsa: Add
support for learning FDB through notification") "to indicate
inconsistent
situation" when we could not delete an FDB entry from the port.

bridge fdb del d8:58:d7:00:ca:6d dev swp0 self master

It is a bit drastic and at the same time not helpful if the above fails
to only print with netdev_dbg log level, but on the other hand to bring
the interface down.

So increase the verbosity of the error message, and drop dev_close().

Signed-off-by: Vladimir Oltean <vladimir.oltean at nxp.com>
---
Changes in v3:
Patch is new.

 net/dsa/slave.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 4a0498bf6c65..d5d389300124 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -2072,7 +2072,9 @@ static void dsa_slave_switchdev_event_work(struct
work_struct *work)
 
 		err = dsa_port_fdb_add(dp, fdb_info->addr, fdb_info->vid);
 		if (err) {
-			netdev_dbg(dev, "fdb add failed err=%d\n", err);
+			netdev_err(dev,
+				   "failed to add %pM vid %d to fdb: %d\n",
+				   fdb_info->addr, fdb_info->vid, err);
 			break;
 		}
 		fdb_info->offloaded = true;
@@ -2087,9 +2089,11 @@ static void dsa_slave_switchdev_event_work(struct
work_struct *work)
 
 		err = dsa_port_fdb_del(dp, fdb_info->addr, fdb_info->vid);
 		if (err) {
-			netdev_dbg(dev, "fdb del failed err=%d\n", err);
-			dev_close(dev);
+			netdev_err(dev,
+				   "failed to delete %pM vid %d from fdb: %d\n",
+				   fdb_info->addr, fdb_info->vid, err);
 		}
+
 		break;
 	}
 	rtnl_unlock();
-- 
2.25.1

Currently DSA doesn't add FDB entries on the CPU port, because it only
does so through switchdev, which is associated with a net_device, and
there are none of those for the CPU port.

But actually FDB addresses on the CPU port have some use cases of their
own, if the switchdev operations are initiated from within the DSA
layer. There is just one problem with the existing code: it passes a
structure in dsa_switchdev_event_work which was retrieved directly from
switchdev, so it contains a net_device. We need to generalize the
contents to something that covers the CPU port as well: the "ds, port"
tuple is fine for that.

Note that the new procedure for notifying the successful FDB offload is
inspired from the rocker model.

Also, nothing was being done if added_by_user was false. Let's check for
that a lot earlier, and don't actually bother to schedule the worker
for nothing.

Signed-off-by: Vladimir Oltean <vladimir.oltean at nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli at gmail.com>
---
Changes in v3:
None.

Changes in v2:
Small cosmetic changes (reverse Christmas notation)

 net/dsa/dsa_priv.h |  12 +++++
 net/dsa/slave.c    | 106 ++++++++++++++++++++++-----------------------
 2 files changed, 65 insertions(+), 53 deletions(-)

diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index 7c96aae9062c..c04225f74929 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -73,6 +73,18 @@ struct dsa_notifier_mtu_info {
 	int mtu;
 };
 
+struct dsa_switchdev_event_work {
+	struct dsa_switch *ds;
+	int port;
+	struct work_struct work;
+	unsigned long event;
+	/* Specific for SWITCHDEV_FDB_ADD_TO_DEVICE and
+	 * SWITCHDEV_FDB_DEL_TO_DEVICE
+	 */
+	unsigned char addr[ETH_ALEN];
+	u16 vid;
+};
+
 struct dsa_slave_priv {
 	/* Copy of CPU port xmit for faster access in slave transmit hot path */
 	struct sk_buff *	(*xmit)(struct sk_buff *skb,
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index d5d389300124..5e4fb44c2820 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -2047,76 +2047,66 @@ static int dsa_slave_netdevice_event(struct
notifier_block *nb,
 	return NOTIFY_DONE;
 }
 
-struct dsa_switchdev_event_work {
-	struct work_struct work;
-	struct switchdev_notifier_fdb_info fdb_info;
-	struct net_device *dev;
-	unsigned long event;
-};
+static void
+dsa_fdb_offload_notify(struct dsa_switchdev_event_work *switchdev_work)
+{
+	struct dsa_switch *ds = switchdev_work->ds;
+	struct switchdev_notifier_fdb_info info;
+	struct dsa_port *dp;
+
+	if (!dsa_is_user_port(ds, switchdev_work->port))
+		return;
+
+	info.addr = switchdev_work->addr;
+	info.vid = switchdev_work->vid;
+	info.offloaded = true;
+	dp = dsa_to_port(ds, switchdev_work->port);
+	call_switchdev_notifiers(SWITCHDEV_FDB_OFFLOADED,
+				 dp->slave, &info.info, NULL);
+}
 
 static void dsa_slave_switchdev_event_work(struct work_struct *work)
 {
 	struct dsa_switchdev_event_work *switchdev_work  		container_of(work, struct
dsa_switchdev_event_work, work);
-	struct net_device *dev = switchdev_work->dev;
-	struct switchdev_notifier_fdb_info *fdb_info;
-	struct dsa_port *dp = dsa_slave_to_port(dev);
+	struct dsa_switch *ds = switchdev_work->ds;
+	struct dsa_port *dp;
 	int err;
 
+	dp = dsa_to_port(ds, switchdev_work->port);
+
 	rtnl_lock();
 	switch (switchdev_work->event) {
 	case SWITCHDEV_FDB_ADD_TO_DEVICE:
-		fdb_info = &switchdev_work->fdb_info;
-		if (!fdb_info->added_by_user)
-			break;
-
-		err = dsa_port_fdb_add(dp, fdb_info->addr, fdb_info->vid);
+		err = dsa_port_fdb_add(dp, switchdev_work->addr,
+				       switchdev_work->vid);
 		if (err) {
-			netdev_err(dev,
-				   "failed to add %pM vid %d to fdb: %d\n",
-				   fdb_info->addr, fdb_info->vid, err);
+			dev_err(ds->dev,
+				"port %d failed to add %pM vid %d to fdb: %d\n",
+				dp->index, switchdev_work->addr,
+				switchdev_work->vid, err);
 			break;
 		}
-		fdb_info->offloaded = true;
-		call_switchdev_notifiers(SWITCHDEV_FDB_OFFLOADED, dev,
-					 &fdb_info->info, NULL);
+		dsa_fdb_offload_notify(switchdev_work);
 		break;
 
 	case SWITCHDEV_FDB_DEL_TO_DEVICE:
-		fdb_info = &switchdev_work->fdb_info;
-		if (!fdb_info->added_by_user)
-			break;
-
-		err = dsa_port_fdb_del(dp, fdb_info->addr, fdb_info->vid);
+		err = dsa_port_fdb_del(dp, switchdev_work->addr,
+				       switchdev_work->vid);
 		if (err) {
-			netdev_err(dev,
-				   "failed to delete %pM vid %d from fdb: %d\n",
-				   fdb_info->addr, fdb_info->vid, err);
+			dev_err(ds->dev,
+				"port %d failed to delete %pM vid %d from fdb: %d\n",
+				dp->index, switchdev_work->addr,
+				switchdev_work->vid, err);
 		}
 
 		break;
 	}
 	rtnl_unlock();
 
-	kfree(switchdev_work->fdb_info.addr);
 	kfree(switchdev_work);
-	dev_put(dev);
-}
-
-static int
-dsa_slave_switchdev_fdb_work_init(struct dsa_switchdev_event_work *
-				  switchdev_work,
-				  const struct switchdev_notifier_fdb_info *
-				  fdb_info)
-{
-	memcpy(&switchdev_work->fdb_info, fdb_info,
-	       sizeof(switchdev_work->fdb_info));
-	switchdev_work->fdb_info.addr = kzalloc(ETH_ALEN, GFP_ATOMIC);
-	if (!switchdev_work->fdb_info.addr)
-		return -ENOMEM;
-	ether_addr_copy((u8 *)switchdev_work->fdb_info.addr,
-			fdb_info->addr);
-	return 0;
+	if (dsa_is_user_port(ds, dp->index))
+		dev_put(dp->slave);
 }
 
 /* Called under rcu_read_lock() */
@@ -2124,7 +2114,9 @@ static int dsa_slave_switchdev_event(struct notifier_block
*unused,
 				     unsigned long event, void *ptr)
 {
 	struct net_device *dev = switchdev_notifier_info_to_dev(ptr);
+	const struct switchdev_notifier_fdb_info *fdb_info;
 	struct dsa_switchdev_event_work *switchdev_work;
+	struct dsa_port *dp;
 	int err;
 
 	if (event == SWITCHDEV_PORT_ATTR_SET) {
@@ -2137,20 +2129,32 @@ static int dsa_slave_switchdev_event(struct
notifier_block *unused,
 	if (!dsa_slave_dev_check(dev))
 		return NOTIFY_DONE;
 
+	dp = dsa_slave_to_port(dev);
+
 	switchdev_work = kzalloc(sizeof(*switchdev_work), GFP_ATOMIC);
 	if (!switchdev_work)
 		return NOTIFY_BAD;
 
 	INIT_WORK(&switchdev_work->work,
 		  dsa_slave_switchdev_event_work);
-	switchdev_work->dev = dev;
+	switchdev_work->ds = dp->ds;
+	switchdev_work->port = dp->index;
 	switchdev_work->event = event;
 
 	switch (event) {
 	case SWITCHDEV_FDB_ADD_TO_DEVICE:
 	case SWITCHDEV_FDB_DEL_TO_DEVICE:
-		if (dsa_slave_switchdev_fdb_work_init(switchdev_work, ptr))
-			goto err_fdb_work_init;
+		fdb_info = ptr;
+
+		if (!fdb_info->added_by_user) {
+			kfree(switchdev_work);
+			return NOTIFY_OK;
+		}
+
+		ether_addr_copy(switchdev_work->addr,
+				fdb_info->addr);
+		switchdev_work->vid = fdb_info->vid;
+
 		dev_hold(dev);
 		break;
 	default:
@@ -2160,10 +2164,6 @@ static int dsa_slave_switchdev_event(struct
notifier_block *unused,
 
 	dsa_schedule_work(&switchdev_work->work);
 	return NOTIFY_OK;
-
-err_fdb_work_init:
-	kfree(switchdev_work);
-	return NOTIFY_BAD;
 }
 
 static int dsa_slave_switchdev_blocking_event(struct notifier_block *unused,
-- 
2.25.1

We'll need to start listening to SWITCHDEV_FDB_{ADD,DEL}_TO_DEVICE
events even for interfaces where dsa_slave_dev_check returns false, so
we need that check inside the switch-case statement for SWITCHDEV_FDB_*.

This movement also avoids a useless allocation / free of switchdev_work
on the untreated "default event" case.

Signed-off-by: Vladimir Oltean <vladimir.oltean at nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli at gmail.com>
---
Changes in v3:
None.

Changes in v2:
None.

 net/dsa/slave.c | 35 ++++++++++++++++-------------------
 1 file changed, 16 insertions(+), 19 deletions(-)

diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 5e4fb44c2820..42ec18a4c7ba 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -2119,31 +2119,29 @@ static int dsa_slave_switchdev_event(struct
notifier_block *unused,
 	struct dsa_port *dp;
 	int err;
 
-	if (event == SWITCHDEV_PORT_ATTR_SET) {
+	switch (event) {
+	case SWITCHDEV_PORT_ATTR_SET:
 		err = switchdev_handle_port_attr_set(dev, ptr,
 						     dsa_slave_dev_check,
 						     dsa_slave_port_attr_set);
 		return notifier_from_errno(err);
-	}
-
-	if (!dsa_slave_dev_check(dev))
-		return NOTIFY_DONE;
+	case SWITCHDEV_FDB_ADD_TO_DEVICE:
+	case SWITCHDEV_FDB_DEL_TO_DEVICE:
+		if (!dsa_slave_dev_check(dev))
+			return NOTIFY_DONE;
 
-	dp = dsa_slave_to_port(dev);
+		dp = dsa_slave_to_port(dev);
 
-	switchdev_work = kzalloc(sizeof(*switchdev_work), GFP_ATOMIC);
-	if (!switchdev_work)
-		return NOTIFY_BAD;
+		switchdev_work = kzalloc(sizeof(*switchdev_work), GFP_ATOMIC);
+		if (!switchdev_work)
+			return NOTIFY_BAD;
 
-	INIT_WORK(&switchdev_work->work,
-		  dsa_slave_switchdev_event_work);
-	switchdev_work->ds = dp->ds;
-	switchdev_work->port = dp->index;
-	switchdev_work->event = event;
+		INIT_WORK(&switchdev_work->work,
+			  dsa_slave_switchdev_event_work);
+		switchdev_work->ds = dp->ds;
+		switchdev_work->port = dp->index;
+		switchdev_work->event = event;
 
-	switch (event) {
-	case SWITCHDEV_FDB_ADD_TO_DEVICE:
-	case SWITCHDEV_FDB_DEL_TO_DEVICE:
 		fdb_info = ptr;
 
 		if (!fdb_info->added_by_user) {
@@ -2156,13 +2154,12 @@ static int dsa_slave_switchdev_event(struct
notifier_block *unused,
 		switchdev_work->vid = fdb_info->vid;
 
 		dev_hold(dev);
+		dsa_schedule_work(&switchdev_work->work);
 		break;
 	default:
-		kfree(switchdev_work);
 		return NOTIFY_DONE;
 	}
 
-	dsa_schedule_work(&switchdev_work->work);
 	return NOTIFY_OK;
 }
 
-- 
2.25.1

Right now, the following would happen for a switch driver that does not
implement .port_fdb_add or .port_fdb_del.

dsa_slave_switchdev_event returns NOTIFY_OK and schedules:
-> dsa_slave_switchdev_event_work
   -> dsa_port_fdb_add
      -> dsa_port_notify(DSA_NOTIFIER_FDB_ADD)
         -> dsa_switch_fdb_add
            -> if (!ds->ops->port_fdb_add) return -EOPNOTSUPP;
   -> an error is printed with dev_dbg, and
      dsa_fdb_offload_notify(switchdev_work) is not called.

We can avoid scheduling the worker for nothing and say NOTIFY_DONE.
Because we don't call dsa_fdb_offload_notify, the static FDB entry will
remain just in the software bridge.

Signed-off-by: Vladimir Oltean <vladimir.oltean at nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli at gmail.com>
---
Changes in v3:
s/NOTIFY_OK/NOTIFY_DONE/ in commit description.

Changes in v2:
Patch is new.

 net/dsa/slave.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 42ec18a4c7ba..37dffe5bc46f 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -2132,6 +2132,9 @@ static int dsa_slave_switchdev_event(struct notifier_block
*unused,
 
 		dp = dsa_slave_to_port(dev);
 
+		if (!dp->ds->ops->port_fdb_add ||
!dp->ds->ops->port_fdb_del)
+			return NOTIFY_DONE;
+
 		switchdev_work = kzalloc(sizeof(*switchdev_work), GFP_ATOMIC);
 		if (!switchdev_work)
 			return NOTIFY_BAD;
-- 
2.25.1

Some DSA switches (and not only) cannot learn source MAC addresses from
packets injected from the CPU. They only perform hardware address
learning from inbound traffic.

This can be problematic when we have a bridge spanning some DSA switch
ports and some non-DSA ports (which we'll call "foreign
interfaces" from
DSA's perspective).

There are 2 classes of problems created by the lack of learning on
CPU-injected traffic:
- excessive flooding, due to the fact that DSA treats those addresses as
  unknown
- the risk of stale routes, which can lead to temporary packet loss

To illustrate the second class, consider the following situation, which
is common in production equipment (wireless access points, where there
is a WLAN interface and an Ethernet switch, and these form a single
bridging domain).

 AP 1:
 +------------------------------------------------------------------------+
 |                                          br0                           |
 +------------------------------------------------------------------------+
 +------------+ +------------+ +------------+ +------------+ +------------+
 |    swp0    | |    swp1    | |    swp2    | |    swp3    | |    wlan0   |
 +------------+ +------------+ +------------+ +------------+ +------------+
       |                                                       ^        ^
       |                                                       |        |
       |                                                       |        |
       |                                                    Client A  Client B
       |
       |
       |
 +------------+ +------------+ +------------+ +------------+ +------------+
 |    swp0    | |    swp1    | |    swp2    | |    swp3    | |    wlan0   |
 +------------+ +------------+ +------------+ +------------+ +------------+
 +------------------------------------------------------------------------+
 |                                          br0                           |
 +------------------------------------------------------------------------+
 AP 2

- br0 of AP 1 will know that Clients A and B are reachable via wlan0
- the hardware fdb of a DSA switch driver today is not kept in sync with
  the software entries on other bridge ports, so it will not know that
  clients A and B are reachable via the CPU port UNLESS the hardware
  switch itself performs SA learning from traffic injected from the CPU.
  Nonetheless, a substantial number of switches don't.
- the hardware fdb of the DSA switch on AP 2 may autonomously learn that
  Client A and B are reachable through swp0. Therefore, the software br0
  of AP 2 also may or may not learn this. In the example we're
  illustrating, some Ethernet traffic has been going on, and br0 from AP
  2 has indeed learnt that it can reach Client B through swp0.

One of the wireless clients, say Client B, disconnects from AP 1 and
roams to AP 2. The topology now looks like this:

 AP 1:
 +------------------------------------------------------------------------+
 |                                          br0                           |
 +------------------------------------------------------------------------+
 +------------+ +------------+ +------------+ +------------+ +------------+
 |    swp0    | |    swp1    | |    swp2    | |    swp3    | |    wlan0   |
 +------------+ +------------+ +------------+ +------------+ +------------+
       |                                                            ^
       |                                                            |
       |                                                         Client A
       |
       |
       |                                                         Client B
       |                                                            |
       |                                                            v
 +------------+ +------------+ +------------+ +------------+ +------------+
 |    swp0    | |    swp1    | |    swp2    | |    swp3    | |    wlan0   |
 +------------+ +------------+ +------------+ +------------+ +------------+
 +------------------------------------------------------------------------+
 |                                          br0                           |
 +------------------------------------------------------------------------+
 AP 2

- br0 of AP 1 still knows that Client A is reachable via wlan0 (no change)
- br0 of AP 1 will (possibly) know that Client B has left wlan0. There
  are cases where it might never find out though. Either way, DSA today
  does not process that notification in any way.
- the hardware FDB of the DSA switch on AP 1 may learn autonomously that
  Client B can be reached via swp0, if it receives any packet with
  Client 1's source MAC address over Ethernet.
- the hardware FDB of the DSA switch on AP 2 still thinks that Client B
  can be reached via swp0. It does not know that it has roamed to wlan0,
  because it doesn't perform SA learning from the CPU port.

Now Client A contacts Client B.
AP 1 routes the packet fine towards swp0 and delivers it on the Ethernet
segment.
AP 2 sees a frame on swp0 and its fdb says that the destination is swp0.
Hairpinning is disabled => drop.

This problem comes from the fact that these switches have a 'blind spot'
for addresses coming from software bridging. The generic solution is not
to assume that hardware learning can be enabled somehow, but to listen
to more bridge learning events. It turns out that the bridge driver does
learn in software from all inbound frames, in __br_handle_local_finish.
A proper SWITCHDEV_FDB_ADD_TO_DEVICE notification is emitted for the
addresses serviced by the bridge on 'foreign' interfaces. The software
bridge also does the right thing on migration, by notifying that the old
entry is deleted, so that does not need to be special-cased in DSA. When
it is deleted, we just need to delete our static FDB entry towards the
CPU too, and wait.

The problem is that DSA currently only cares about SWITCHDEV_FDB_ADD_TO_DEVICE
events received on its own interfaces, such as static FDB entries.

Luckily we can change that, and DSA can listen to all switchdev FDB
add/del events in the system and figure out if those events were emitted
by a bridge that spans at least one of DSA's own ports. In case that is
true, DSA will also offload that address towards its own CPU port, in
the eventuality that there might be bridge clients attached to the DSA
switch who want to talk to the station connected to the foreign
interface.

In terms of implementation, we need to keep the fdb_info->added_by_user
check for the case where the switchdev event was targeted directly at a
DSA switch port. But we don't need to look at that flag for snooped
events. So the check is currently too late, we need to move it earlier.
This also simplifies the code a bit, since we avoid uselessly allocating
and freeing switchdev_work.

We could probably do some improvements in the future. For example,
multi-bridge support is rudimentary at the moment. If there are two
bridges spanning a DSA switch's ports, and both of them need to service
the same MAC address, then what will happen is that the migration of one
of those stations will trigger the deletion of the FDB entry from the
CPU port while it is still used by other bridge. That could be improved
with reference counting but is left for another time.

This behavior needs to be enabled at driver level by setting
ds->assisted_learning_on_cpu_port = true. This is because we don't want
to inflict a potential performance penalty (accesses through
MDIO/I2C/SPI are expensive) to hardware that really doesn't need it
because address learning on the CPU port works there.

Reported-by: DENG Qingfang <dqfext at gmail.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean at nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli at gmail.com>
---
Changes in v3:
- s/learning_broken/assisted_learning/
- don't call dev_hold unless it's a DSA slave interface, to avoid broken
  refcounting

Changes in v2:
Made the behavior conditional.

 include/net/dsa.h |  5 ++++
 net/dsa/slave.c   | 66 +++++++++++++++++++++++++++++++++++++++--------
 2 files changed, 60 insertions(+), 11 deletions(-)

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 4e60d2610f20..6b74690bd8d4 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -319,6 +319,11 @@ struct dsa_switch {
 	 */
 	bool			untag_bridge_pvid;
 
+	/* Let DSA manage the FDB entries towards the CPU, based on the
+	 * software bridge database.
+	 */
+	bool			assisted_learning_on_cpu_port;
+
 	/* In case vlan_filtering_is_global is set, the VLAN awareness state
 	 * should be retrieved from here and not from the per-port settings.
 	 */
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 37dffe5bc46f..456576f75a50 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -2109,6 +2109,28 @@ static void dsa_slave_switchdev_event_work(struct
work_struct *work)
 		dev_put(dp->slave);
 }
 
+static int dsa_lower_dev_walk(struct net_device *lower_dev,
+			      struct netdev_nested_priv *priv)
+{
+	if (dsa_slave_dev_check(lower_dev)) {
+		priv->data = (void *)netdev_priv(lower_dev);
+		return 1;
+	}
+
+	return 0;
+}
+
+static struct dsa_slave_priv *dsa_slave_dev_lower_find(struct net_device *dev)
+{
+	struct netdev_nested_priv priv = {
+		.data = NULL,
+	};
+
+	netdev_walk_all_lower_dev_rcu(dev, dsa_lower_dev_walk, &priv);
+
+	return (struct dsa_slave_priv *)priv.data;
+}
+
 /* Called under rcu_read_lock() */
 static int dsa_slave_switchdev_event(struct notifier_block *unused,
 				     unsigned long event, void *ptr)
@@ -2127,10 +2149,37 @@ static int dsa_slave_switchdev_event(struct
notifier_block *unused,
 		return notifier_from_errno(err);
 	case SWITCHDEV_FDB_ADD_TO_DEVICE:
 	case SWITCHDEV_FDB_DEL_TO_DEVICE:
-		if (!dsa_slave_dev_check(dev))
-			return NOTIFY_DONE;
+		fdb_info = ptr;
 
-		dp = dsa_slave_to_port(dev);
+		if (dsa_slave_dev_check(dev)) {
+			if (!fdb_info->added_by_user)
+				return NOTIFY_OK;
+
+			dp = dsa_slave_to_port(dev);
+		} else {
+			/* Snoop addresses learnt on foreign interfaces
+			 * bridged with us, for switches that don't
+			 * automatically learn SA from CPU-injected traffic
+			 */
+			struct net_device *br_dev;
+			struct dsa_slave_priv *p;
+
+			br_dev = netdev_master_upper_dev_get_rcu(dev);
+			if (!br_dev)
+				return NOTIFY_DONE;
+
+			if (!netif_is_bridge_master(br_dev))
+				return NOTIFY_DONE;
+
+			p = dsa_slave_dev_lower_find(br_dev);
+			if (!p)
+				return NOTIFY_DONE;
+
+			dp = p->dp->cpu_dp;
+
+			if (!dp->ds->assisted_learning_on_cpu_port)
+				return NOTIFY_DONE;
+		}
 
 		if (!dp->ds->ops->port_fdb_add ||
!dp->ds->ops->port_fdb_del)
 			return NOTIFY_DONE;
@@ -2145,18 +2194,13 @@ static int dsa_slave_switchdev_event(struct
notifier_block *unused,
 		switchdev_work->port = dp->index;
 		switchdev_work->event = event;
 
-		fdb_info = ptr;
-
-		if (!fdb_info->added_by_user) {
-			kfree(switchdev_work);
-			return NOTIFY_OK;
-		}
-
 		ether_addr_copy(switchdev_work->addr,
 				fdb_info->addr);
 		switchdev_work->vid = fdb_info->vid;
 
-		dev_hold(dev);
+		/* Hold a reference on the slave for dsa_fdb_offload_notify */
+		if (dsa_is_user_port(dp->ds, dp->index))
+			dev_hold(dev);
 		dsa_schedule_work(&switchdev_work->work);
 		break;
 	default:
-- 
2.25.1

Given the following setup:

ip link add br0 type bridge
ip link set eno0 master br0
ip link set swp0 master br0
ip link set swp1 master br0
ip link set swp2 master br0
ip link set swp3 master br0

Currently, packets received on a DSA slave interface (such as swp0)
which should be routed by the software bridge towards a non-switch port
(such as eno0) are also flooded towards the other switch ports (swp1,
swp2, swp3) because the destination is unknown to the hardware switch.

This patch addresses the issue by monitoring the addresses learnt by the
software bridge on eno0, and adding/deleting them as static FDB entries
on the CPU port accordingly.

Signed-off-by: Vladimir Oltean <vladimir.oltean at nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli at gmail.com>
---
Changes in v2:
s/learning_broken/assisted_learning/

Changes in v2:
Patch is new.

 drivers/net/dsa/ocelot/felix.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/dsa/ocelot/felix.c b/drivers/net/dsa/ocelot/felix.c
index 7dc230677b78..90c3c76f21b2 100644
--- a/drivers/net/dsa/ocelot/felix.c
+++ b/drivers/net/dsa/ocelot/felix.c
@@ -629,6 +629,7 @@ static int felix_setup(struct dsa_switch *ds)
 
 	ds->mtu_enforcement_ingress = true;
 	ds->configure_vlan_while_not_filtering = true;
+	ds->assisted_learning_on_cpu_port = true;
 
 	return 0;
 }
-- 
2.25.1