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

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Message-ID: <1294161623.3831.643.camel@zakaz.uk.xensource.com>
Date:	Tue, 4 Jan 2011 17:20:23 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jn Beulich <JBeulich@...ell.com>,
	"Konrad Rzeszutek Wilk" <konrad@...nel.org>,
	"hpa@...or.com" <hpa@...or.com>
Subject: Re: [Xen-devel] Re: [PATCH 2/8] xen/mmu: Add the notion of
 identity (1-1) mapping.

On Tue, 2011-01-04 at 16:59 +0000, Ian Campbell wrote:
> 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.

I should have read patch 5/8 first...

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