linux-kernel - Re: [Xen-devel] [PATCH 03/10] xen/mmu: Add the notion of IDENTITY_P2M

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Date:	Wed, 22 Dec 2010 08:44:19 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jeremy@...p.org" <jeremy@...p.org>,
	"hpa@...or.com" <hpa@...or.com>,
	Konrad Rzeszutek Wilk <konrad@...nel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Jan Beulich <JBeulich@...ell.com>
Subject: Re: [Xen-devel] [PATCH 03/10] xen/mmu: Add the notion of
 IDENTITY_P2M_ENTRY.

On Tue, 2010-12-21 at 21:37 +0000, Konrad Rzeszutek Wilk wrote: 
> P.S.
> We cannot set the IDENTITY_P2M_ENTRY in the P2M tree. This is b/c
> the toolstack considers that invalid and would abort during
> migration of the PV guest.

What do we do instead, just write the actual identity MFN value?

Does using 1UL<<30 (or 1UL<<62 on 64 bit, note that Jeremy recently
fixed FOREIGN_FRAME_BIT too) as IDENTITY_P2M_ENTRY keep the toolstack
happy while still allowing us to distinguish from identity from
happens-to-be-the-same as necessary?

To some extent 1-1 I/O regions could be considered foreign mappings (of
"memory" owned by DOMIO) so perhaps it's possible that setting the
FOREIGN_FRAME_BIT is both sufficient and correct?

Ian.

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