From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [Xen-devel] [PATCHv1 net-next] xen-netback: remove unconditional pull_skb_tail in guest Tx path Date: Tue, 04 Nov 2014 16:17:04 -0500 (EST) Message-ID: <20141104.161704.1690311989900127361.davem@davemloft.net> References: <1415036346.1411.3.camel@citrix.com> <5457BF80.2000205@citrix.com> <5457C807.5080509@linaro.org> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: david.vrabel@citrix.com, Ian.Campbell@citrix.com, netdev@vger.kernel.org, malcolm.crossley@citrix.com, wei.liu2@citrix.com, xen-devel@lists.xenproject.org To: zoltan.kiss@linaro.org Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:59500 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751176AbaKDVRH (ORCPT ); Tue, 4 Nov 2014 16:17:07 -0500 In-Reply-To: <5457C807.5080509@linaro.org> Sender: netdev-owner@vger.kernel.org List-ID: From: Zoltan Kiss Date: Mon, 03 Nov 2014 18:23:03 +0000 > > > On 03/11/14 17:46, David Vrabel wrote: >> On 03/11/14 17:39, Ian Campbell wrote: >>> On Mon, 2014-11-03 at 17:23 +0000, David Vrabel wrote: >>>> From: Malcolm Crossley >>>> >>>> Unconditionally pulling 128 bytes into the linear buffer is not >>>> required. Netback has already grant copied up-to 128 bytes from the >>>> first slot of a packet into the linear buffer. The first slot normally >>>> contain all the IPv4/IPv6 and TCP/UDP headers. >>> >>> What about when it doesn't? It sounds as if we now won't pull up, >>> which >>> would be bad. >> >> The network stack will always pull any headers it needs to inspect >> (the >> frag may be a userspace page which has the same security issues as a >> frag with a foreign page). > I wouldn't bet my life on this, but indeed it should always happen. I would bet my life on it. Every protocol demux starts with pskb_may_pull() to pull frag data into the linear area, if necessary, before looking at headers.