From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net v4] xen-netback: Fix grant ref resolution in RX path Date: Thu, 15 May 2014 23:33:01 -0400 (EDT) Message-ID: <20140515.233301.1125896512771744526.davem@davemloft.net> References: <1400148514-2921-1-git-send-email-zoltan.kiss@citrix.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: xen-devel@lists.xenproject.org, ian.campbell@citrix.com, wei.liu2@citrix.com, linux@eikelenboom.it, paul.durrant@citrix.com, netdev@vger.kernel.org, david.vrabel@citrix.com To: zoltan.kiss@citrix.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:38949 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752610AbaEPDdD (ORCPT ); Thu, 15 May 2014 23:33:03 -0400 In-Reply-To: <1400148514-2921-1-git-send-email-zoltan.kiss@citrix.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Zoltan Kiss Date: Thu, 15 May 2014 11:08:34 +0100 > The original series for reintroducing grant mapping for netback had a patch [1] > to handle receiving of packets from an another VIF. Grant copy on the receiving > side needs the grant ref of the page to set up the op. > The original patch assumed (wrongly) that the frags array haven't changed. In > the case reported by Sander, the sending guest sent a packet where the linear > buffer and the first frag were under PKT_PROT_LEN (=128) bytes. > xenvif_tx_submit() then pulled up the linear area to 128 bytes, and ditched the > first frag. The receiving side had an off-by-one problem when gathered the grant > refs. > This patch fixes that by checking whether the actual frag's page pointer is the > same as the page in the original frag list. It can handle any kind of changes on > the original frags array, like: > - removing granted frags from the array at any point > - adding local pages to the frags list anywhere > - reordering the frags > It's optimized to the most common case, when there is 1:1 relation between the > frags and the list, plus works optimal when frags are removed from the end or > the beginning. > > [1]: 3e2234: xen-netback: Handle foreign mapped pages on the guest RX path > > Reported-by: Sander Eikelenboom > Signed-off-by: Zoltan Kiss Applied, thanks everyone.