On 7/16/2025 2:26 AM, Ido Schimmel wrote:
On Mon, Jul 14, 2025 at 11:01:00AM -0400, Joseph Huang wrote:
Do not offload IGMP/MLD messages as it could lead to IGMP/MLD Reports
being unintentionally flooded to Hosts. Instead, let the bridge decide
where to send these IGMP/MLD messages.
Consider the case where the local host is sending out reports in response
to a remote querier like the following:
mcast-listener-process (IP_ADD_MEMBERSHIP)
\
br0
/ \
swp1 swp2
| |
QUERIER SOME-OTHER-HOST
In the above setup, br0 will want to br_forward() reports for
mcast-listener-process's group(s) via swp1 to QUERIER; but since the
source hwdom is 0, the report is eligible for tx offloading, and is
flooded by hardware to both swp1 and swp2, reaching SOME-OTHER-HOST as
well. (Example and illustration provided by Tobias.)
Fixes: 472111920f1c ("net: bridge: switchdev: allow the TX data plane forwarding to be offloaded")
Signed-off-by: Joseph Huang <Joseph.Huang@xxxxxxxxxx>
I don't have personal experience with this offload, but it makes sense
to not offload the replication of control packets to the underlying
device and instead let the CPU handle it. These shouldn't be sent at an
high rate anyway.
I think you can just early return if the packet is IGMP/MLD. Something
like:
diff --git a/net/bridge/br_switchdev.c b/net/bridge/br_switchdev.c
index 95d7355a0407..9a910cf0256e 100644
--- a/net/bridge/br_switchdev.c
+++ b/net/bridge/br_switchdev.c
@@ -17,6 +17,9 @@ static bool nbp_switchdev_can_offload_tx_fwd(const struct net_bridge_port *p,
if (!static_branch_unlikely(&br_switchdev_tx_fwd_offload))
return false;
+ if (br_multicast_igmp_type(skb))
+ return false;
+
return (p->flags & BR_TX_FWD_OFFLOAD) &&
(p->hwdom != BR_INPUT_SKB_CB(skb)->src_hwdom);
}
Talking about these packets being low rate, should I add unlikely() like so:
diff --git a/net/bridge/br_switchdev.c b/net/bridge/br_switchdev.c
index 95d7355a0407..9a910cf0256e 100644
--- a/net/bridge/br_switchdev.c
+++ b/net/bridge/br_switchdev.c
@@ -17,6 +17,9 @@ static bool nbp_switchdev_can_offload_tx_fwd(const
struct net_bridge_port *p,
if (!static_branch_unlikely(&br_switchdev_tx_fwd_offload))
return false;
+ if (unlikely(br_multicast_igmp_type(skb)))
+ return false;
+
return (p->flags & BR_TX_FWD_OFFLOAD) &&
(p->hwdom != BR_INPUT_SKB_CB(skb)->src_hwdom);
}
Thanks,
Joseph
