From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4D811C43381 for ; Tue, 19 Feb 2019 17:54:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2C57720855 for ; Tue, 19 Feb 2019 17:54:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726321AbfBSRyk (ORCPT ); Tue, 19 Feb 2019 12:54:40 -0500 Received: from mail-wr1-f65.google.com ([209.85.221.65]:39853 "EHLO mail-wr1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725936AbfBSRyj (ORCPT ); Tue, 19 Feb 2019 12:54:39 -0500 Received: by mail-wr1-f65.google.com with SMTP id l5so21886957wrw.6 for ; Tue, 19 Feb 2019 09:54:38 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=DBe1JIetxZeZLToQy/udQtZwVV8m9GNSABXbNuJKbow=; b=LNvpOLhVHhlTrh9gbgdhobmUvmCajri7qQZ97NflhIHcGyorCZfOHoBpQWVcpr02MQ A5dq2OHZCJMang1bSckNy471l3moAfjFx1AHm0b9qN/uTmHhk5rOCBA3F9ssL+HOSdK2 t8zgCo+6cy0dvUuxxoEJWiOMa/X0LxwBwNIUP5uNrrqSMZTNlCceWRxuaBpmbXzuHf3+ 2LdAVh87TJ7/KtCuTzvWOrOIB6PA2yoQwxpn+mIT5AsAE6rAUig9Vzgb5QAMkflnFj4r yAtxEkdPJtimESkEqpV/jwfXuGnRIAJG1GEvgLyZu5vPLK9bNpRqPLjMpRQ51dGPoBd0 /oOw== X-Gm-Message-State: AHQUAubHr1yG5nj4IisESJKqBmSjZ20Qie3VOGMWHbmLZTKKOzjeZGoA 3kYB0ZxqDSnuISr3dmnQPeVO/g+6wmI= X-Google-Smtp-Source: AHgI3IZW2/LyoUiWz2JemzvGYlhbsHIk2Ws/IaOUCYkY5O3RNL9Rxy+RMtDd+XgveiFOoCQmOLJfZw== X-Received: by 2002:a5d:4147:: with SMTP id c7mr22839107wrq.235.1550598877936; Tue, 19 Feb 2019 09:54:37 -0800 (PST) Received: from pc-2.home (2a01cb05850ddf00045dd60e6368f84b.ipv6.abo.wanadoo.fr. [2a01:cb05:850d:df00:45d:d60e:6368:f84b]) by smtp.gmail.com with ESMTPSA id b4sm4935911wmj.3.2019.02.19.09.54.36 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 19 Feb 2019 09:54:37 -0800 (PST) Date: Tue, 19 Feb 2019 18:54:35 +0100 From: Guillaume Nault To: James Chapman Cc: t.martitz@avm.de, davem@davemloft.net, netdev Subject: Re: L2TPv3 offset Message-ID: <20190219175434.GA31500@pc-2.home> References: <40957000-591c-c871-ddf5-89e05fa958d0@katalix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Feb 19, 2019 at 04:36:55PM +0000, James Chapman wrote: > On 19/02/2019 13:09, t.martitz@avm.de wrote: > > > > Because everytime a LCCE decapsulates such traffic it'll suffer from > > unaligned access to the inner IP header (likewise for the outer IP > > header when encapsulating). It's a fundamental assumption that the IP > > header is word-aligned in Linux so I'm surprised this isn't solved > > already. And now the only way "fix" without patching the kernel is > > being removed. > > IIUC, you'd be perfectly fine running without offset if the stack was properly handling the alignment problems created by the encapsulated ethernet header. Unaligned headers is a fundamental problem when tunneling ethernet frames. I'd expect other encapsulation modules (vxlan, geneve, gretap...) to have the same issues (but I'd be happy to be proven wrong). The topic has been discussed a few years ago: https://lore.kernel.org/netdev/20160922.015242.735026657310158125.davem@davemloft.net/ I might very well have missed some discussions, but I don't remember any patch aimed at tackling this problem so far.