net: dsa: tag_brcm: do not mark link local traffic as offloaded

[PATCH net] net: dsa: tag_brcm: do not mark link local traffic as offloaded

Posted by Jonas Gorski 1 month, 1 week ago

Broadcom switches locally terminate link local traffic and do not
forward it, so we should not mark it as offloaded.

In some situations we still want/need to flood this traffic, e.g. if STP
is disabled, or it is explicitly enabled via the group_fwd_mask. But if
the skb is marked as offloaded, the kernel will assume this was already
done in hardware, and the packets never reach other bridge ports.

So ensure that link local traffic is never marked as offloaded, so that
the kernel can forward/flood these packets in software if needed.

Since the local termination in not configurable, check the destination
MAC, and never mark packets as offloaded if it is a link local ether
address.

While modern switches set the tag reason code to BRCM_EG_RC_PROT_TERM
for trapped link local traffic, they also set it for link local traffic
that is flooded (01:80:c2:00:00:10 to 01:80:c2:00:00:2f), so we cannot
use it and need to look at the destination address for them as well.

Fixes: 964dbf186eaa ("net: dsa: tag_brcm: add support for legacy tags")
Fixes: 0e62f543bed0 ("net: dsa: Fix duplicate frames flooded by learning")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
---
I shortly considered changing dsa_default_offload_fwd_mark(), but
decided against it because other switches may have a working trap bit,
and would then do a needless destination mac check.

I used likely() because br_input.c uses
unlikely(is_link_local_ether_addr()), and that seemed reasonable.

 net/dsa/tag_brcm.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/dsa/tag_brcm.c b/net/dsa/tag_brcm.c
index d9c77fa553b5..eadb358179ce 100644
--- a/net/dsa/tag_brcm.c
+++ b/net/dsa/tag_brcm.c
@@ -176,7 +176,8 @@ static struct sk_buff *brcm_tag_rcv_ll(struct sk_buff *skb,
 	/* Remove Broadcom tag and update checksum */
 	skb_pull_rcsum(skb, BRCM_TAG_LEN);
 
-	dsa_default_offload_fwd_mark(skb);
+	if (likely(!is_link_local_ether_addr(eth_hdr(skb)->h_dest)))
+		dsa_default_offload_fwd_mark(skb);
 
 	return skb;
 }
@@ -250,7 +251,8 @@ static struct sk_buff *brcm_leg_tag_rcv(struct sk_buff *skb,
 	/* Remove Broadcom tag and update checksum */
 	skb_pull_rcsum(skb, len);
 
-	dsa_default_offload_fwd_mark(skb);
+	if (likely(!is_link_local_ether_addr(eth_hdr(skb)->h_dest)))
+		dsa_default_offload_fwd_mark(skb);
 
 	dsa_strip_etype_header(skb, len);
 

base-commit: 96a9178a29a6b84bb632ebeb4e84cf61191c73d5
-- 
2.43.0

Re: [PATCH net] net: dsa: tag_brcm: do not mark link local traffic as offloaded

Posted by Florian Fainelli 1 month, 1 week ago

On November 9, 2025 5:46:35 AM PST, Jonas Gorski <jonas.gorski@gmail.com> wrote:
>Broadcom switches locally terminate link local traffic and do not
>forward it, so we should not mark it as offloaded.
>
>In some situations we still want/need to flood this traffic, e.g. if STP
>is disabled, or it is explicitly enabled via the group_fwd_mask. But if
>the skb is marked as offloaded, the kernel will assume this was already
>done in hardware, and the packets never reach other bridge ports.
>
>So ensure that link local traffic is never marked as offloaded, so that
>the kernel can forward/flood these packets in software if needed.
>
>Since the local termination in not configurable, check the destination
>MAC, and never mark packets as offloaded if it is a link local ether
>address.
>
>While modern switches set the tag reason code to BRCM_EG_RC_PROT_TERM
>for trapped link local traffic, they also set it for link local traffic
>that is flooded (01:80:c2:00:00:10 to 01:80:c2:00:00:2f), so we cannot
>use it and need to look at the destination address for them as well.
>
>Fixes: 964dbf186eaa ("net: dsa: tag_brcm: add support for legacy tags")
>Fixes: 0e62f543bed0 ("net: dsa: Fix duplicate frames flooded by learning")
>Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>

Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>

Florian

Re: [PATCH net] net: dsa: tag_brcm: do not mark link local traffic as offloaded

Posted by Vladimir Oltean 1 month, 1 week ago

On Sun, Nov 09, 2025 at 02:46:35PM +0100, Jonas Gorski wrote:
> Broadcom switches locally terminate link local traffic and do not
> forward it, so we should not mark it as offloaded.
> 
> In some situations we still want/need to flood this traffic, e.g. if STP
> is disabled, or it is explicitly enabled via the group_fwd_mask. But if
> the skb is marked as offloaded, the kernel will assume this was already
> done in hardware, and the packets never reach other bridge ports.
> 
> So ensure that link local traffic is never marked as offloaded, so that
> the kernel can forward/flood these packets in software if needed.
> 
> Since the local termination in not configurable, check the destination
> MAC, and never mark packets as offloaded if it is a link local ether
> address.
> 
> While modern switches set the tag reason code to BRCM_EG_RC_PROT_TERM
> for trapped link local traffic, they also set it for link local traffic
> that is flooded (01:80:c2:00:00:10 to 01:80:c2:00:00:2f), so we cannot
> use it and need to look at the destination address for them as well.
> 
> Fixes: 964dbf186eaa ("net: dsa: tag_brcm: add support for legacy tags")
> Fixes: 0e62f543bed0 ("net: dsa: Fix duplicate frames flooded by learning")
> Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
> ---
> I shortly considered changing dsa_default_offload_fwd_mark(), but
> decided against it because other switches may have a working trap bit,
> and would then do a needless destination mac check.

Yes, exactly. Or they simply don't receive link-local traffic via packet traps.

Reviewed-by: Vladimir Oltean <olteanv@gmail.com>