netdev - Re: [PATCH] net: fec: fix regression on i.MX28 introduced by rx

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Date:	Tue, 07 Oct 2014 07:27:14 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Lothar Waßmann <LW@...O-electronics.de>
Cc:	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
Subject: Re: [PATCH] net: fec: fix regression on i.MX28 introduced by
 rx_copybreak support

On Tue, 2014-10-07 at 15:19 +0200, Lothar Waßmann wrote:
> 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.
> 
> Signed-off-by: Lothar Waßmann <LW@...O-electronics.de>
> ---
>  drivers/net/ethernet/freescale/fec_main.c |   25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> index 87975b5..eaaebad 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -339,6 +339,18 @@ static void *swap_buffer(void *bufaddr, int len)
>  	return bufaddr;
>  }
>  
> +static void *swap_buffer2(void *dst_buf, void *src_buf, int len)
> +{
> +	int i;
> +	unsigned int *src = src_buf;
> +	unsigned int *dst = dst_buf;
> +
> +	for (i = 0; i < DIV_ROUND_UP(len, 4); i++, src++, dst++)
> +		*dst = cpu_to_be32(*src);

No need for the DIV :

	for (i = 0; i < len; i += sizeof(*dst), src++, dst++)
		*dst = cpu_to_be32(*src);

Also are you sure both src/dst are aligned to word boundaries, or is
this architecture OK with possible misalignment ?



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