netdev - Re: [PATCH] xfrm: Add pre-encap fragmentation for packet offload

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Message-ID: <20241124120424.GE160612@unreal>
Date: Sun, 24 Nov 2024 14:04:24 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Ilia Lin <ilia.lin@...nel.org>
Cc: steffen.klassert@...unet.com, herbert@...dor.apana.org.au,
	davem@...emloft.net, dsahern@...nel.org, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, horms@...nel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xfrm: Add pre-encap fragmentation for packet offload

On Sun, Nov 24, 2024 at 11:35:31AM +0200, Ilia Lin wrote:
> In packet offload mode the raw packets will be sent to the NiC,
> and will not return to the Network Stack. In event of crossing
> the MTU size after the encapsulation, the NiC HW may not be
> able to fragment the final packet.

Yes, HW doesn't know how to handle these packets.

> Adding mandatory pre-encapsulation fragmentation for both
> IPv4 and IPv6, if tunnel mode with packet offload is configured
> on the state.

I was under impression is that xfrm_dev_offload_ok() is responsible to
prevent fragmentation.
https://elixir.bootlin.com/linux/v6.12/source/net/xfrm/xfrm_device.c#L410

Thanks