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

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Message-ID: <alpine.DEB.2.00.1109291550250.3519@kaball-desktop>
Date:	Thu, 29 Sep 2011 15:53:47 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Ian Campbell <Ian.Campbell@...citrix.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	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, 29 Sep 2011, Ian Campbell wrote:
> 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.

It was needed by the previous version that was capable of handling
highmem pages, it is not required anymore.
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