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SubjectRe: [Stable-review] [22/68] ixgbe: prevent speculative processing of descriptors before ready
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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@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:
> >
> > commit a124339ad28389093ed15eca990d39c51c5736cc
> > Author: Don Skidmore <donald.c.skidmore@intel.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@kernel.org
> > Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
> > Tested-by: Stephen Ko <stephen.s.ko@intel.com>
> > Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.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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