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

To: "Jan Kiszka" <jan.kiszka@xxxxxxxxxxx>
Subject: [Xen-devel] RE: How to generate a HW NMI
From: "Roger Cruz" <roger.cruz@xxxxxxxxxxxxxxxxxxx>
Date: Mon, 4 Oct 2010 08:56:03 -0500
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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Thread-topic: How to generate a HW NMI


I will try your suggestion of turning off SMIs.  I am also interested in you conducting an experiment for me.  If you can, please tell your kernel not to use any CPU power saving modes.  In Xen I use max_cstate=0 in the bootline.  I have found that when I do this, the hangs appear to go away (we had one customer report one since using this work-around, so it is not 100% working).


-----Original Message-----
From: Jan Kiszka [mailto:jan.kiszka@xxxxxxxxxxx]
Sent: Mon 10/4/2010 6:27 AM
To: Roger Cruz
Cc: Konrad Rzeszutek Wilk; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: How to generate a HW NMI

Am 01.10.2010 21:33, Roger Cruz wrote:
> 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.

We happen to face strange freezes of KVM right now as well (CPU is
apparently stuck in guest mode), and turning of SMIs cures them here
[1]. However, it's too early to draw final conclusions, we are still
collecting test results & data on the systems.

It would therefore be interesting to see if you case is similar to ours.
If you feel brave enough to turn off your SMIs (there are rumors that
CPUs /could/ get fried as some thermal management /might/ be done via
SMIs), please check out [2], build it (requires libpci and a kernel
source tree), and run "smitctrl -s 0" on your box. Should give something
like this:

SMI-enabled chipset found:
 SMI_EN register:       0006403b
 new value:             00000002

If the chipset is not detected, add the PCI device ID of your ISA bridge
to the list in smictrl.c. If the new value still has bit 0 set, you are
unlucky as your BIOS has locked some SMIs against disabling. Otherwise,
SMIs are off now, and your lock up /may/ disappear. Looking forward to
your results!


[1] http://thread.gmane.org/gmane.comp.emulators.kvm.devel/60326
[2] http://git.kiszka.org/?p=smictrl.git

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