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RE: [Xen-devel] PoD in other (not GPLPV) drivers

To: "George Dunlap" <george.dunlap@xxxxxxxxxx>
Subject: RE: [Xen-devel] PoD in other (not GPLPV) drivers
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Thu, 3 Mar 2011 21:22:21 +1100
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] PoD in other (not GPLPV) drivers
> On Mon, 2011-02-28 at 22:20 +0000, James Harper wrote:
> > Is there a way for DomU to get an interrupt when an unpopulated page is
> > hit when the DomU has gone past its initial limit? That would allow me
> > to at least write a message to the log and crash usefully if I can't do
> > anything else about it.
> At the moment there's no mechanism for this.  Doing so would be a bit
> tricky, as most of the places which do gfn_to_mfn() translations aren't
> designed to handle failures gracefully (although that may have changed
> since some of the guest paging stuff was introduced).
> If we were to do this at some point in the future, what do you think
> you'd like the interface to look like?  (i.e., deliver NMI? MCE? a
> different but well-known interrupt?  &c)

I don't know that there is a sactioned way to intercept an NMI under windows. 
An MCE would do the trick probably. Basically I want the user to know that 
their VM crashed because it hit the PoD limit, rather than have no idea why it 
crashed. Most of the time if a user gets a crash I ask for a copy of 
/var/log/xen/qemu-dm-<domu>.log, so if the message appeared there then that 
would be fine with me too.

I was under the impression that xen would blow the DomU up if it overstepped 
its PoD limit, but now I'm not so sure as I've seen windows BSoD with lots of 
different bug check codes when it happens. What should happen? I think that 
instant death is the only sensible outcome.


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