linux-kernel - Re: [PATCH 3/5] lguest: avoid accidental recycling of pgdir pages

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Message-Id: <200903271154.22450.rusty@rustcorp.com.au>
Date:	Fri, 27 Mar 2009 11:54:20 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	lguest@...abs.org, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 3/5] lguest: avoid accidental recycling of pgdir pages

On Friday 27 March 2009 10:47:32 Jeremy Fitzhardinge wrote:
> Rusty Russell wrote:
> > Impact: potential bugfix
> >
> > In theory, the kernel could reuse the same page as pgdir for a new process
> > while the hypervisor keeps it cached.  This would have undesirable results.
> >   
> 
> You can't just do this in tlb flush?

I don't think so.  The problem is that lguest tracks 4 toplevels, using random
replacement.  This cache is indexed by cr3 value.

Lguest assumes it's told about all pte removals or changes, but simple
additions get faulted in.  If a pgdir page gets reused we'll potentially have
stale values from its previous life as a pgdir, no?

Now, I haven't *seen* this happen...
Rusty.
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