linux-kernel - RE: [PATCHv2 6/6] net: fec: fix regression on i.MX28 introduced by rx

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1C9E04C0@AcuExch.aculab.com>
Date:	Tue, 28 Oct 2014 11:12:30 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Lothar Waßmann' <LW@...O-electronics.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	"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>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCHv2 6/6] net: fec: fix regression on i.MX28 introduced by
 rx_copybreak support

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.
> 
> Signed-off-by: Lothar Wamann <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 404fb9d..b92324c 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 < len; i += 4, src++, dst++)
> +		swab32s(src);

This will probably benefit from being unrolled slightly.
Neither 'dst' nor the return value is used.

> +
> +	return dst_buf;
> +}
> +
>  static void fec_dump(struct net_device *ndev)
>  {
>  	struct fec_enet_private *fep = netdev_priv(ndev);
> @@ -1334,7 +1346,7 @@ fec_enet_new_rxbdp(struct net_device *ndev, struct bufdesc *bdp, struct sk_buff
>  }
> 
>  static bool fec_enet_copybreak(struct net_device *ndev, struct sk_buff **skb,
> -			       struct bufdesc *bdp, u32 length)
> +			       struct bufdesc *bdp, u32 length, bool swap)
>  {
>  	struct  fec_enet_private *fep = netdev_priv(ndev);
>  	struct sk_buff *new_skb;
> @@ -1349,7 +1361,10 @@ static bool fec_enet_copybreak(struct net_device *ndev, struct sk_buff **skb,
>  	dma_sync_single_for_cpu(&fep->pdev->dev, bdp->cbd_bufaddr,
>  				FEC_ENET_RX_FRSIZE - fep->rx_align,
>  				DMA_FROM_DEVICE);
> -	memcpy(new_skb->data, (*skb)->data, length);
> +	if (!swap)
> +		memcpy(new_skb->data, (*skb)->data, length);
> +	else
> +		swap_buffer2(new_skb->data, (*skb)->data, length);
>  	*skb = new_skb;
> 
>  	return true;
> @@ -1377,6 +1392,7 @@ fec_enet_rx_queue(struct net_device *ndev, int budget, u16 queue_id)
>  	u16	vlan_tag;
>  	int	index = 0;
>  	bool	is_copybreak;
> +	bool	need_swap = fep->quirks & FEC_QUIRK_SWAP_FRAME;
> 
>  #ifdef CONFIG_M532x
>  	flush_cache_all();
> @@ -1440,7 +1456,8 @@ fec_enet_rx_queue(struct net_device *ndev, int budget, u16 queue_id)
>  		 * include that when passing upstream as it messes up
>  		 * bridging applications.
>  		 */
> -		is_copybreak = fec_enet_copybreak(ndev, &skb, bdp, pkt_len - 4);
> +		is_copybreak = fec_enet_copybreak(ndev, &skb, bdp, pkt_len - 4,
> +						  need_swap);
>  		if (!is_copybreak) {
>  			skb_new = netdev_alloc_skb(ndev, FEC_ENET_RX_FRSIZE);
>  			if (unlikely(!skb_new)) {
> @@ -1455,7 +1472,7 @@ fec_enet_rx_queue(struct net_device *ndev, int budget, u16 queue_id)
>  		prefetch(skb->data - NET_IP_ALIGN);
>  		skb_put(skb, pkt_len - 4);
>  		data = skb->data;
> -		if (fep->quirks & FEC_QUIRK_SWAP_FRAME)
> +		if (!is_copybreak && need_swap)
>  			swap_buffer(data, pkt_len);

It has to be better to set the 'copybreak' limit to be larger than the
maximum frame size and so always go through the 'copybreak' paths.

> 
>  		/* Extract the enhanced buffer descriptor */
> --
> 1.7.10.4
> 
> --
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