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

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Message-ID: <Z0g3A87ArEdrOCgj@gauss3.secunet.de>
Date: Thu, 28 Nov 2024 10:25:23 +0100
From: Steffen Klassert <steffen.klassert@...unet.com>
To: Leon Romanovsky <leon@...nel.org>
CC: Ilia Lin <ilia.lin@...nel.org>, <herbert@...dor.apana.org.au>, "David
 Miller" <davem@...emloft.net>, <dsahern@...nel.org>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <horms@...nel.org>,
	<netdev@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xfrm: Add pre-encap fragmentation for packet offload

On Tue, Nov 26, 2024 at 03:21:45PM +0200, Leon Romanovsky wrote:
> On Tue, Nov 26, 2024 at 01:59:31PM +0100, Steffen Klassert wrote:
> > On Tue, Nov 26, 2024 at 10:35:13AM +0200, Leon Romanovsky wrote:
> > > 
> > > Steffen, do we need special case for packet offload here? My preference is
> > > to make sure that we will have as less possible special cases for packet
> > > offload.
> > 
> > Looks like the problem on packet offload is that packets
> > bigger than MTU size are dropped before the PMTU signaling
> > is handled.
> 
> But PMTU should be less or equal to MTU, even before first packet was
> sent. Otherwise already first packet will be fragmented.

Atually I ment PMTU. On packet offload, we just drop packets bigger
than PMTU. We need to make sure that xfrm{4,6}_tunnel_check_size
is called. This will either fragment or do PMTU signaling.