[PATCH net] net: stmmac: fix the invalid VID programmed by VLAN perfect filtering

[PATCH net] net: stmmac: fix the invalid VID programmed by VLAN perfect filtering

[Linkui Xiao]

From: Linkui Xiao <xiaolinkui@kylinos.cn>

for_each_set_bit() leaves its iterator equal to the bitmap size once the
loop terminates, so the 'vid' read after the loop in stmmac_vlan_update()
is always VLAN_N_VID (4096) and never the last VLAN ID that was found.

Cores that do not support VLAN hash filtering (dma_cap.vlhash == 0) fall
back to the single VID perfect match filter and hand that value straight
to the MAC. vlan_update_hash() therefore programs MAC_VLAN_Tag with
VID 4096, a value that can never match an incoming 802.1Q tag, so the
perfect filter ends up discarding all VLAN tagged traffic. Both
stmmac_test_vlanfilt_perfect() and stmmac_test_dvlanfilt_perfect() walk
this path and fail as a result.

Remember the VID while iterating so that the last active VLAN ID is the
one passed to the perfect match filter. When hash filtering is available
'hash' is non-zero as soon as at least one VID is active, so
vlan_update_hash() keeps ignoring 'pmatch' and nothing changes there.

Fixes: c7ab0b8088d7 ("net: stmmac: Fallback to VLAN Perfect filtering if HASH is not available")
Cc: stable@vger.kernel.org
Signed-off-by: Linkui Xiao <xiaolinkui@kylinos.cn>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 62c3441911e7..af2d38a2bb3d 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -6844,13 +6844,13 @@ static int stmmac_vlan_update(struct stmmac_priv *priv, bool is_double)
 		crc = bitrev32(~stmmac_vid_crc32_le(vid_le)) >> 28;
 		hash |= (1 << crc);
 		count++;
+		pmatch = vid;
 	}
 
 	if (!priv->dma_cap.vlhash) {
 		if (count > 2) /* VID = 0 always passes filter */
 			return -EOPNOTSUPP;
 
-		pmatch = vid;
 		hash = 0;
 	}
 
-- 
2.25.1

Re: [PATCH net] net: stmmac: fix the invalid VID programmed by VLAN perfect filtering

[Maxime Chevallier]

Hi,

+Ovidiu

On 9/17/26 14:22, Linkui Xiao wrote:
> From: Linkui Xiao <xiaolinkui@kylinos.cn>
> 
> for_each_set_bit() leaves its iterator equal to the bitmap size once the
> loop terminates, so the 'vid' read after the loop in stmmac_vlan_update()
> is always VLAN_N_VID (4096) and never the last VLAN ID that was found.
> 
> Cores that do not support VLAN hash filtering (dma_cap.vlhash == 0) fall
> back to the single VID perfect match filter and hand that value straight
> to the MAC. vlan_update_hash() therefore programs MAC_VLAN_Tag with
> VID 4096, a value that can never match an incoming 802.1Q tag, so the
> perfect filter ends up discarding all VLAN tagged traffic. Both
> stmmac_test_vlanfilt_perfect() and stmmac_test_dvlanfilt_perfect() walk
> this path and fail as a result.
> 
> Remember the VID while iterating so that the last active VLAN ID is the
> one passed to the perfect match filter. When hash filtering is available
> 'hash' is non-zero as soon as at least one VID is active, so
> vlan_update_hash() keeps ignoring 'pmatch' and nothing changes there.
> 
> Fixes: c7ab0b8088d7 ("net: stmmac: Fallback to VLAN Perfect filtering if HASH is not available")
> Cc: stable@vger.kernel.org
> Signed-off-by: Linkui Xiao <xiaolinkui@kylinos.cn>

Thank you for proposing this fix, however this code is currently being removed :

https://lore.kernel.org/r/20260908164309.59282-1-ovidiu.panait.rb@renesas.com

So no need for this patch :)

Maxime

Re: [PATCH net] net: stmmac: fix the invalid VID programmed by VLAN perfect filtering

[Linkui Xiao]

Hi Maxime,

On 2026/9/17 23:57, Maxime Chevallier wrote:
> Hi,
> 
> +Ovidiu
> 
> On 9/17/26 14:22, Linkui Xiao wrote:
>> From: Linkui Xiao <xiaolinkui@kylinos.cn>
>>
>> for_each_set_bit() leaves its iterator equal to the bitmap size once the
>> loop terminates, so the 'vid' read after the loop in stmmac_vlan_update()
>> is always VLAN_N_VID (4096) and never the last VLAN ID that was found.
>>
>> Cores that do not support VLAN hash filtering (dma_cap.vlhash == 0) fall
>> back to the single VID perfect match filter and hand that value straight
>> to the MAC. vlan_update_hash() therefore programs MAC_VLAN_Tag with
>> VID 4096, a value that can never match an incoming 802.1Q tag, so the
>> perfect filter ends up discarding all VLAN tagged traffic. Both
>> stmmac_test_vlanfilt_perfect() and stmmac_test_dvlanfilt_perfect() walk
>> this path and fail as a result.
>>
>> Remember the VID while iterating so that the last active VLAN ID is the
>> one passed to the perfect match filter. When hash filtering is available
>> 'hash' is non-zero as soon as at least one VID is active, so
>> vlan_update_hash() keeps ignoring 'pmatch' and nothing changes there.
>>
>> Fixes: c7ab0b8088d7 ("net: stmmac: Fallback to VLAN Perfect filtering if HASH is not available")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Linkui Xiao <xiaolinkui@kylinos.cn>
> 
> Thank you for proposing this fix, however this code is currently being removed :
> 
> https://lore.kernel.org/r/20260908164309.59282-1-ovidiu.panait.rb@renesas.com
> 
> So no need for this patch :)

Thanks for the heads-up. I'll drop this patch then.

Ovidiu, I'll keep an eye on your series. If the fallback path
still needs a valid VID after the removal, feel free to ping me.

Thanks,
Linkui
> 
> Maxime