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

["miltonm" <miltonm@bga.com>]

----- Original Message Follows -----
From: Ben Hutchings <ben@decadent.org.uk>
To: Greg KH <gregkh@suse.de>
Cc: linux-kernel@vger.kernel.org, stable@kernel.org, Don
Skidmore <donald.c.skidmore@intel.com>, Milton Miller
<miltonm@bga.com>, "David S. Miller" <davem@davemloft.net>,
Anton Blanchard <anton@samba.org>,
akpm@linux-foundation.org,  torvalds@linux-foundation.org,
stable-review@kernel.org,  alan@lxorguk.ukuu.org.uk, Jeff
Kirsher <jeffrey.t.kirsher@intel.com>
Subject: Re: [Stable-review] [22/68] ixgbe: prevent
speculative processing of descriptors before ready
Date: Tue, 01 Mar 2011 02:14:33 +0000

> 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@bga.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:

This was initially observed on 82598 and is still needed
there.

milton