-----Original Message-----
From: Wood Scott-B07421
Sent: Tuesday, March 05, 2013 7:46 AM
To: Stuart Yoder
Cc: Jia Hongtao-B38951; linuxppc-dev@lists.ozlabs.org; Kumar Gala
Subject: Re: [PATCH V4] powerpc/85xx: Add machine check handler to fix
PCIe erratum on mpc85xx
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On 03/04/2013 10:16:10 AM, Stuart Yoder wrote:

quoted

On Mon, Mar 4, 2013 at 2:40 AM, Jia Hongtao [off-list ref]
wrote:

quoted

A PCIe erratum of mpc85xx may causes a core hang when a link of PCIe
goes down. when the link goes down, Non-posted transactions issued
via the ATMU requiring completion result in an instruction stall.
At the same time a machine-check exception is generated to the core
to allow further processing by the handler. We implements the

handler

quoted

which skips the instruction caused the stall.

Can you explain at a high level how just skipping an instruction
solves
anything?   If you just skip a load/store and continue like nothing is
wrong, isn't your system possibly in a really bad state.

=20
If the instruction was a load, we probably at least want to fill the
destination register with 0xffffffff or similar.

You discuss this with Liu Shuo about a year ago.
here is the log:

"
On 02/01/2012 02:18 AM, shuo.liu@freescale.com wrote:

v3 : Skip the instruction only. Don't access the user space memory in=20
     mechine check.=20

It may be the least bad option for now, but be aware that there's a
small chance that this will cause a leak of sensitive information (such
as a piece of a crypto key that happened to be sitting in the register
to be loaded into).

-Scott
"

-Hongtao.

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quoted

And if the core is already hung, due to the PCI link going down, isn't
it too late?   How does skipping help?

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Maybe the machine check unhangs the core?
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Is there an erratum number for this?
=20
-Scott