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

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Date:	Fri, 15 Jan 2016 21:52:14 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	ivecera@...hat.com
Cc:	netdev@...r.kernel.org, rasesh.mody@...gic.com
Subject: Re: [PATCH net] bna: fix Rx data corruption with VLAN stripping
 enabled and MTU > 4096

From: Ivan Vecera <ivecera@...hat.com>
Date: Fri, 15 Jan 2016 13:45:28 +0100

> 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.
> 
> Cc: Rasesh Mody <rasesh.mody@...gic.com>
> Signed-off-by: Ivan Vecera <ivecera@...hat.com>

Applied, thanks.