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

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Date:	Tue, 01 Mar 2011 22:51:17 -0600
From:	"miltonm" <miltonm@....com>
To:	Ben Hutchings <ben@...adent.org.uk>, Greg KH <gregkh@...e.de>
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



----- Original Message Follows -----
From: Ben Hutchings <ben@...adent.org.uk>
To: Greg KH <gregkh@...e.de>
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
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@....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
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