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RE: [Xen-devel] How to generate a HW NMI

To: "Konrad Rzeszutek Wilk" <konrad.wilk@xxxxxxxxxx>
Subject: RE: [Xen-devel] How to generate a HW NMI
From: "Roger Cruz" <roger.cruz@xxxxxxxxxxxxxxxxxxx>
Date: Fri, 1 Oct 2010 14:33:20 -0500
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Thread-topic: [Xen-devel] How to generate a HW NMI
Great ideas Konrad.  I have ordered these parts.  It will probably take
a few days before they get here.
The goal of using the HW NMI is to rule out any incorrect SW settings of
the Performance Monitoring counters used in Xen to triggered the NMI.

Someone else mentioned that another possibility as to why an NMI may not
be triggered is that the system is stuck handling an SMI interrupt.  I
haven't studied Xen code with respect to SMIs yet, but I assume that Xen
doesn't do much in that area right?  I was under the impression that the
BIOS usually set this up and the OSs could not even modify the handlers
as they were in protected RAM.


-----Original Message-----
From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx] 
Sent: Friday, October 01, 2010 10:15 AM
To: Roger Cruz
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] How to generate a HW NMI

On Thu, Sep 30, 2010 at 12:59:25PM -0500, Roger Cruz wrote:
> Hi fellow Xen developers,
> I continue to get system hangs where the watchdog NMI in Xen is not
> doing its job.  I am completely blind as to what is getting jammed.
> Tried multiple experiments to force the hang and in each, the watchdog
> has kicked in, so I know the mechanism works 99% of the time except in
> my one hang.
> So in the old days of PCI bus, I used to be able to generate a HW NMI
> asserting the SERR signal in the connector.  With the advent of PCIe,


> believe that signal is no longer present, so I am looking for any
> way to cause a system error.    I have examined the PCI express

What about the Mini PCI-e to PCI-e adapter:

And then plug in a PCI to PCI-e adapter:


And then assert the SERR#?

> mini-card specification looking for a signal I can use in the internal
> WiFi connector, but alas, none of the signals I read about seem like
> they would do what I need.  I am not sure if there is anything I can
> short in the PCIe signals that could have a similar effect as the SERR

Per this slide deck:
it looks as if you can program the PCIe bridge to fall to "legacy" mode.

And per some folks post:

it looks as if the SERR# signal is asserted on SMBus controller?
Maybe there is a way to do it via that?

> signal.  The platform is a Lenovo T500 laptop so the number of
> connectors to play with is limited.

IBM on the server sides used to have NMI buttons - it could be that
hadn't completly gotten rid of them. Since you are open to looking at
motherboard, maybe there is a spot marked #NMI ?

> I also thought of causing a parity/ECC error but the GM45 chipset used
> in this laptop does not support ECC memory.

> So I'm basically looking for any other ideas on how to cause a fault
> probing somewhere in the motherboard.  This MB has a docking station
> connector but I have not been able to find the pinout list so I don't
> know what is brought out there.  At this point, I have no problem

How about just shorting the pins randomly :-)

> cracking up the case and soldering something on to the motherboard.. I
> just need to know what chips and signals to tap.
> Thanks in advance.
> Roger R. Cruz

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