netdev - RE: [PATCH net] bna: fix Rx data corruption with VLAN stripping enabled and MTU

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Date:	Sat, 16 Jan 2016 01:27:08 +0000
From:	Rasesh Mody <rasesh.mody@...gic.com>
To:	Ivan Vecera <ivecera@...hat.com>,
	David Miller <davem@...emloft.net>
CC:	netdev <netdev@...r.kernel.org>
Subject: RE: [PATCH net] bna: fix Rx data corruption with VLAN stripping
 enabled and MTU > 4096

> From: Ivan Vecera [mailto:ivecera@...hat.com]
> Sent: Friday, January 15, 2016 4:45 AM
> 
> The multi-buffer Rx mode implemented in the past introduced a regression
> that causes a data corruption for received VLAN traffic when VLAN tag
> stripping is enabled. This mode is supported only be newer chipsets (1860)
> and is enabled when MTU > 4096.
> 
> When this mode is enabled Rx queue contains buffers with fixed size
> 2048 bytes. Any incoming packet larger than 2048 is divided into multiple
> buffers that are attached as skb frags in polling routine.
> 
> The driver assumes that all buffers associated with a packet except the last
> one is fully used (e.g. packet with size 5000 are divided into 3 buffers 2048 +
> 2048 + 904 bytes) and ignores true size reported in completions. This
> assumption is usually true but not when VLAN packet is received and VLAN
> tag stripping is enabled. In this case the first buffer is 2044 bytes long but as
> the driver always assumes
> 2048 bytes then 4 extra random bytes are included between the first and the
> second frag. Additionally the driver sets checksum as correct so the packet is
> properly processed by the core.
> 
> The driver needs to check the size of used space in each Rx buffer reported
> by FW and not blindly use the fixed value.

Looks good to me, thanks Ivan!
Reviewed-by: Rasesh Mody <rasesh.mody@...gic.com>

David - please apply.