linux-kernel - Re: [PATCH 2/8] xen/mmu: Add the notion of identity (1-1) mapping.

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Date:	Tue, 04 Jan 2011 16:59:19 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"hpa@...or.com" <hpa@...or.com>, Jan Beulich <JBeulich@...ell.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Konrad Rzeszutek Wilk <konrad@...nel.org>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>
Subject: Re: [PATCH 2/8] xen/mmu: Add the notion of identity (1-1) mapping.

On Tue, 2011-01-04 at 16:53 +0000, Ian Campbell wrote:
> 
> If I do "__set_phys_to_machine(X, X)" where X happens to currently
> correspond to p2m_mid_missing won't that cause all pfn entries in the
> range covered by p2m_top[topidx] (i.e. quite a few, like 512^2 pages
> or
> something) to switch from missing to identity? Similarly for
> p2m_top[topidx][mididx]?
> 
> Perhaps ranges of identity bits are often well aligned with the
> boundaries in the p2m 3-level tree but wouldn't that just be
> coincidence? 

I wonder if it would make sense to have a debugfs file which exports the
p2m, for the purposes of eye-balling it for this sort of issue?
comparing to the e820 etc...

Maybe the whole thing in raw form would be overkill but spitting out a
list of ranges of identity, invalid, normal pages, plus annotation
regarding whether those come from a p2m_mid_identity style page or a
leaf node, might be occasionally useful.

Ian.
-- 
Ian Campbell
Current Noise: Place of Skulls - The Watchers

Call toll free number before digging.

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