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

From: Tony Nguyen <anthony.l.nguyen@intel.com>
To: Erwan Velu <e.velu@criteo.com>, Brett Creeley <bcreeley@amd.com>,
	"Erwan Velu" <erwanaliasr1@gmail.com>
Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	<intel-wired-lan@lists.osuosl.org>, <netdev@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 iwl-net] i40e: Prevent setting MTU if greater than MFS
Date: Thu, 14 Mar 2024 13:31:33 -0700	[thread overview]
Message-ID: <8f4724f8-e831-12f6-d4e1-4700ea47b2a0@intel.com> (raw)
In-Reply-To: <7b612db6-cec6-4873-8a38-fb4c97192aa2@criteo.com>

On 3/14/2024 11:04 AM, Erwan Velu wrote:
> 
> Le 14/03/2024 à 18:55, Brett Creeley a écrit :
>> [...]
>> 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.
> 
> Sorry Brett, I was probably unclear and please note that I'm not a 
> network developer, just a user that faced a bug.
> 
> My initial though was to check the mfs size in i40e_change_mtu() and if 
> mfs is too small, then let's increase it.
> 
> Maybe just resetting it at init time to the largest value (which seems 
> to be the default fw behavior) is a best approach.
> 
> I'd love to ear from Intel dev that knows this driver/cards/fw better on 
> what's the best approach here.

Setting the mfs size to max values during init and reset would better; 
this is what the ice driver does. However, this would take implementing 
new AdminQ calls. IMO this patch is ok to prevent the issue being 
reported and allow for ease of backport.

Thanks,
Tony