From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lothar =?UTF-8?B?V2HDn21hbm4=?= Subject: Re: [PATCH] net: fec: fix regression on i.MX28 introduced by rx_copybreak support Date: Wed, 8 Oct 2014 06:59:21 +0200 Message-ID: <20141008065921.068385a6@ipc1.ka-ro> References: <1412687977-11742-1-git-send-email-LW@KARO-electronics.de> <063D6719AE5E284EB5DD2968C1650D6D174C6025@AcuExch.aculab.com> <20141007161702.7cd1e800@ipc1.ka-ro> <063D6719AE5E284EB5DD2968C1650D6D174C60B1@AcuExch.aculab.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: "netdev@vger.kernel.org" , "David S. Miller" , Russell King , Frank Li , Fabio Estevam , "linux-kernel@vger.kernel.org" To: David Laight Return-path: Received: from mail.karo-electronics.de ([81.173.242.67]:51594 "EHLO mail.karo-electronics.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754539AbaJHE70 convert rfc822-to-8bit (ORCPT ); Wed, 8 Oct 2014 00:59:26 -0400 In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D174C60B1@AcuExch.aculab.com> Sender: netdev-owner@vger.kernel.org List-ID: Hi, David Laight wrote: > From: Lothar > > David Laight wrote: > > > From: Lothar Wa=C3=9Fmann > > > > commit 1b7bde6d659d ("net: fec: implement rx_copybreak to impro= ve rx performance") > > > > introduced a regression for i.MX28. The swap_buffer() function = doing > > > > the endian conversion of the received data on i.MX28 may access= memory > > > > beyond the actual packet size in the DMA buffer. fec_enet_copyb= reak() > > > > does not copy those bytes, so that the last bytes of a packet m= ay be > > > > filled with invalid data after swapping. > > > > This will likely lead to checksum errors on received packets. > > > > E.g. when trying to mount an NFS rootfs: > > > > UDP: bad checksum. From 192.168.1.225:111 to 192.168.100.73:446= 62 ulen 36 > > > > > > > > Do the byte swapping and copying to the new skb in one go if > > > > necessary. > > > > > > ISTM that if you need to do the 'swap' you should copy the data r= egardless > > > of the length. > > > > > The swap function has to look at at most 3 bytes beyond the actual > > packet length. That is what the original swap_buffer() function doe= s and > > what the new function swap_buffer2(), that does the endian swapping > > while copying to the new buffer, also does. >=20 > I understood the bug. >=20 > The point I was making is that if you have to do a read-write of the = received > data (to byteswap it) then you might as well always copy it into a ne= w skb that > is just big enough for the actual receive frame. >=20 I wanted to use the least intrusive solution. Lothar Wa=C3=9Fmann --=20 ___________________________________________________________ Ka-Ro electronics GmbH | Pascalstra=C3=9Fe 22 | D - 52076 Aachen Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10 Gesch=C3=A4ftsf=C3=BChrer: Matthias Kaussen Handelsregistereintrag: Amtsgericht Aachen, HRB 4996 www.karo-electronics.de | info@karo-electronics.de ___________________________________________________________