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

[Stefano Stabellini]

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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