Re: [PATCH net] net: mana: Fall back to standard MTU when PF reports adapter_mtu of 0

[Simon Horman]

On Thu, Jun 18, 2026 at 10:53:38PM -0700, Erni Sri Satya Vennela wrote:
> Commit d7709812e13d ("net: mana: hardening: Validate adapter_mtu from
> MANA_QUERY_DEV_CONFIG") rejected any adapter_mtu value smaller than
> ETH_MIN_MTU + ETH_HLEN, including 0, returning -EPROTO and failing
> mana_probe().
> 
> Some older PF firmware versions still in the field report
> adapter_mtu as 0 in the MANA_QUERY_DEV_CONFIG response. With the
> hardening check in place, the MANA VF driver now fails to load on
> those hosts, breaking networking entirely for guests.
> 
> MANA hardware always supports the standard Ethernet MTU. Treat a
> reported adapter_mtu of 0 as "the PF did not advertise a value" and
> fall back to ETH_FRAME_LEN, the same value used for the pre-V2
> message version path. Only jumbo frames remain unavailable until
> the PF reports a valid MTU.
> 
> Other small-but-nonzero bogus values are still rejected, preserving
> the original protection against the unsigned-subtraction wrap that
> would otherwise let ndev->max_mtu underflow to a huge value.
> 
> Fixes: d7709812e13d ("net: mana: hardening: Validate adapter_mtu from MANA_QUERY_DEV_CONFIG")
> Signed-off-by: Erni Sri Satya Vennela <ernis@xxxxxxxxxxxxxxxxxxx>

Reviewed-by: Simon Horman <horms@xxxxxxxxxx>

FTR, I agree with your assessment that the issue flagged in the
AI-generated review of this patch on sashiko.dev can be
treated as a follow-up [1].

And I don't think the low priority issue flagged in the AI-generated
review on https://netdev-ai.bots.linux.dev/sashiko/ should impede progress
of this patch.

[1] https://lore.kernel.org/bpf/ajj+5mhswcqhI2z7@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/