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

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Message-ID: <1299016580.3187.98.camel@jtkirshe-MOBL1>
Date:	Tue, 01 Mar 2011 13:56:20 -0800
From:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:	Greg KH <gregkh@...e.de>
Cc:	Ben Hutchings <ben@...adent.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...nel.org" <stable@...nel.org>,
	"Skidmore, Donald C" <donald.c.skidmore@...el.com>,
	Milton Miller <miltonm@....com>,
	"David S. Miller" <davem@...emloft.net>,
	Anton Blanchard <anton@...ba.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	"stable-review@...nel.org" <stable-review@...nel.org>,
	"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>
Subject: Re: [Stable-review] [22/68] ixgbe: prevent speculative processing
 of descriptors before ready

On Tue, 2011-03-01 at 12:46 -0800, Greg KH wrote:
> 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

Don is working on patch for .32 kernel, I hope to send it out no later
than tomorrow.

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