linux-kernel - Re: [PATCH v4 iwl-net] i40e: Prevent setting MTU if greater than MFS

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Date: Thu, 14 Mar 2024 10:55:02 -0700
From: Brett Creeley <bcreeley@....com>
To: Erwan Velu <e.velu@...teo.com>, Erwan Velu <erwanaliasr1@...il.com>
Cc: Jesse Brandeburg <jesse.brandeburg@...el.com>,
 Tony Nguyen <anthony.l.nguyen@...el.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 iwl-net] i40e: Prevent setting MTU if greater than MFS

On 3/14/2024 10:10 AM, Erwan Velu wrote:
> Caution: This message originated from an External Source. Use proper 
> caution when opening attachments, clicking links, or responding.
> 
> 
> Le 14/03/2024 à 17:10, Brett Creeley a écrit :
> [...]
>> If this is how the max_mtu is determined, does it make sense to set this
>> before registering the netdev, i.e. netdev->max_mtu in
>> i40e_config_netdev()?
> 
> 
> The absolute max is properly set but I think that's only true if we
> ensure the value of the MFS.
> 
> So if with another patch to set the MFS to the right value when asking a
> bigger MTU, having this value makes sense this is the absolute max for
> this device.

AFAIK there is no API for a user to change the max_mtu, so the only way 
the device's MFS would need to change is if it's done during 
initialization time, which should be done before netdev registration anyway.

I guess it's also possible that the driver's XDP configuration could 
cause a change in the device's MFS and netdev->max_mtu, but that would 
be under the rtnl_lock.

Seems like others are happy with it, but FWIW that's my 2 cents, 
otherwise LGTM.

Reviewed-by: Brett Creeley <brett.creeley@....com>

> 
> 
> Erwan,
>