| Message ID | 20201213140710.1198050-2-vladimir.oltean@nxp.com (mailing list archive) |
|---|---|
| State | Deferred |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | Offload software learnt bridge addresses to DSA | expand |
| Context | Check | Description |
|---|---|---|
| netdev/cover_letter | success | Link |
| netdev/fixes_present | success | Link |
| netdev/patch_count | success | Link |
| netdev/tree_selection | success | Clearly marked for net-next |
| netdev/subject_prefix | success | Link |
| netdev/source_inline | success | Was 0 now: 0 |
| netdev/verify_signedoff | success | Link |
| netdev/module_param | success | Was 0 now: 0 |
| netdev/build_32bit | success | Errors and warnings before: 0 this patch: 0 |
| netdev/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| netdev/verify_fixes | success | Link |
| netdev/checkpatch | success | total: 0 errors, 0 warnings, 0 checks, 7 lines checked |
| netdev/build_allmodconfig_warn | success | Errors and warnings before: 0 this patch: 0 |
| netdev/header_inline | success | Link |
| netdev/stable | success | Stable not CCed |
On Sun, Dec 13, 2020 at 04:07:04PM +0200, Vladimir Oltean wrote: > 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. Can you please clarify why the FDB replacement notification is not enough? Is it because the hardware you are working with manages MACs to CPU in a separate table from its FDB table? I assume that's why you refer to it as a "rule" instead of FDB entry? How common is this with DSA switches? Asking because it is not clear to me from the commit message. The patch looks fine. > > 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@nxp.com> > Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com> Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Hi Ido, On Sun, Dec 13, 2020 at 04:55:43PM +0200, Ido Schimmel wrote: > > 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. > > Can you please clarify why the FDB replacement notification is not > enough? I didn't say it is not enough. I said it is a whole lot harder to track from the listener side. > Is it because the hardware you are working with manages MACs to > CPU in a separate table from its FDB table? I assume that's why you > refer to it as a "rule" instead of FDB entry? How common is this with > DSA switches? With DSA switches it's just more generic to use a static FDB entry as the address trapping rule. But since FDB entries are global across the switch and not really per source port, understandably other mechanisms such as an ACL entry could be used just as well. And an ACL is what other drivers (like drivers/staging/fsl-dpaa2/ethsw/) would use for this purpose (of course, the code is not there yet; it's still in staging, there are other issues to resolve first). The mechanism does really not matter though, as long as it's "strong" and not "weak" (i.e. the entry cannot be overridden by hardware address learning on the front panel ports). So when the bridge gets any clue that the L2 routing information is no longer up to date, the very least we must do is we must delete this trapping rule to give the hardware a chance to learn again. Where the address is migrated to is really not as important as the fact that it migrated in the first place. [ ok, then there's the case where it migrates from a foreign interface to another foreign interface. For that scenario, we would delete the trapping rule and then reinstall it, which is not ideal but also not incorrect. ] > Reviewed-by: Ido Schimmel <idosch@nvidia.com> Thanks.
On Sun, Dec 13, 2020 at 04:07:04PM +0200, Vladimir Oltean wrote: > 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. Reviewed-by: Andrew Lunn <andrew@lunn.ch> Andrew
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 */
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@nxp.com> Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com> --- Changes in v3: None. Changes in v2: Patch is new. net/bridge/br_fdb.c | 1 + 1 file changed, 1 insertion(+)