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[Xen-devel] Re: shadow2 corrupting PV guest state

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Michael A Fetterman <Michael.Fetterman@xxxxxxxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: shadow2 corrupting PV guest state
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sat, 14 Oct 2006 08:05:55 +0100
Cc: Chris Wright <chrisw@xxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 14/10/06 12:27 am, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx> wrote:

> All a bit handwavy, but I haven't really managed to make much headway.
> I spent some time assuming it was a bug on my side, but the fact that
> all these symptoms go away with pre-shadow2 Xen makes me point the
> finger over the wall.
> 
> Or perhaps it really is just a qemu bug, but I can't imagine that
> shadow2 exercises qemu's emulated CPU exception stuff in a way which
> normal Xen doesn't...  I think its more likely that there's some race
> which is much more easily triggered by qemu's slow speed.
> 
> Any thoughts or ideas?

The shadow-refcount code in shadow2 is very new. It's likely to have bugs
that need shaking out. It won't be a deferred pagetable update because they
don't exist in shadow2 (updates are always synchronously emulated).

 -- Keir



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