linux-kernel - Re: [Stable-review] [22/68] ixgbe: prevent speculative processing of descriptors before ready

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Date:	Tue, 1 Mar 2011 15:46:12 -0500
From:	Greg KH <gregkh@...e.de>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	Don Skidmore <donald.c.skidmore@...el.com>,
	Milton Miller <miltonm@....com>,
	"David S. Miller" <davem@...emloft.net>,
	Anton Blanchard <anton@...ba.org>, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, stable-review@...nel.org,
	alan@...rguk.ukuu.org.uk,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: Re: [Stable-review] [22/68] ixgbe: prevent speculative processing
 of descriptors before ready

On Tue, Mar 01, 2011 at 02:14:33AM +0000, Ben Hutchings wrote:
> On Mon, 2011-02-28 at 08:22 -0800, Greg KH wrote:
> > 2.6.32-longterm review patch.  If anyone has any objections, please let us know.
> > 
> > ------------------
> > 
> > From: Milton Miller <miltonm@....com>
> > 
> > commit 3c945e5b3719bcc18c6ddd31bbcae8ef94f3d19a upstream.
> > 
> > The PowerPC architecture does not require loads to independent bytes to be
> > ordered without adding an explicit barrier.
> > 
> > In ixgbe_clean_rx_irq we load the status bit then load the packet data.
> > With packet split disabled if these loads go out of order we get a
> > stale packet, but we will notice the bad sequence numbers and drop it.
> > 
> > The problem occurs with packet split enabled where the TCP/IP header and data
> > are in different descriptors. If the reads go out of order we may have data
> > that doesn't match the TCP/IP header. Since we use hardware checksumming this
> > bad data is never verified and it makes it all the way to the application.
> [...]
> 
> Packet splitting should be completely disabled on the 82599, anyway.
> Greg, what happened to this patch:
> 
> commit a124339ad28389093ed15eca990d39c51c5736cc
> Author: Don Skidmore <donald.c.skidmore@...el.com>
> Date:   Tue Jan 18 22:53:47 2011 +0000
> 
>     ixgbe: fix for 82599 erratum on Header Splitting
>     
>     We have found a hardware erratum on 82599 hardware that can lead to
>     unpredictable behavior when Header Splitting mode is enabled.  So
>     we are no longer enabling this feature on affected hardware.
>     
>     Please see the 82599 Specification Update for more information.
>     
>     CC: stable@...nel.org
>     Signed-off-by: Don Skidmore <donald.c.skidmore@...el.com>
>     Tested-by: Stephen Ko <stephen.s.ko@...el.com>
>     Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>

It does not apply to the .32 kernel.

Care to provide a backport if you feel it should be there?

thanks,

greg k-h
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