linux-kernel - Re: [Xen-devel] [PATCH v5 2/2] xen: modify kernel mappings corresponding to granted pages

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Date:	Thu, 29 Sep 2011 15:18:04 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"jeremy@...p.org" <jeremy@...p.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH v5 2/2] xen: modify kernel mappings
 corresponding to granted pages

On Thu, 2011-09-29 at 14:55 +0100, Konrad Rzeszutek Wilk wrote:
> >  /* Xen machine address */
> > @@ -31,8 +32,10 @@ typedef struct xpaddr {
> >  #define INVALID_P2M_ENTRY	(~0UL)
> >  #define FOREIGN_FRAME_BIT	(1UL<<(BITS_PER_LONG-1))
> >  #define IDENTITY_FRAME_BIT	(1UL<<(BITS_PER_LONG-2))
> > +#define GRANT_FRAME_BIT	(1UL<<(BITS_PER_LONG-3))
> 
> I am going to change that to (BITS_PER_LONG-1) as we aren't
> using the P2M. (and add that comment in the file).

You should also move it away from/out of the "/**** MACHINE <-> PHYSICAL
CONVERSION MACROS ****/" section, otherwise it's just confusing.

The associated GRANT_FRAME macro seems to be unused.

But what is that bit in page->private actually used for? This patch adds
it in m2p_add_override and masks it off in m2p_find_override, but
doesn't otherwise appear to use it.

Ian.

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