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Date: Wed, 8 Oct 2014 06:59:21 +0200 From: Lothar Waßmann <LW@...O-electronics.de> To: David Laight <David.Laight@...LAB.COM> Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>, Russell King <rmk+kernel@....linux.org.uk>, Frank Li <Frank.Li@...escale.com>, Fabio Estevam <fabio.estevam@...escale.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] net: fec: fix regression on i.MX28 introduced by rx_copybreak support Hi, David Laight wrote: > From: Lothar > > David Laight wrote: > > > From: Lothar Waßmann > > > > commit 1b7bde6d659d ("net: fec: implement rx_copybreak to improve 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_copybreak() > > > > does not copy those bytes, so that the last bytes of a packet may 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 192.168.100.73:44662 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 regardless > > > 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 does and > > what the new function swap_buffer2(), that does the endian swapping > > while copying to the new buffer, also does. > > I understood the bug. > > 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 new skb that > is just big enough for the actual receive frame. > I wanted to use the least intrusive solution. Lothar Waßmann -- ___________________________________________________________ Ka-Ro electronics GmbH | Pascalstraße 22 | D - 52076 Aachen Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10 Geschäftsführer: Matthias Kaussen Handelsregistereintrag: Amtsgericht Aachen, HRB 4996 www.karo-electronics.de | info@...o-electronics.de ___________________________________________________________ -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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