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Date: Thu, 5 Jul 2012 01:05:47 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
To: Rik van Riel <riel@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Hillf Danton <dhillf@gmail.com>, Dan Smith <danms@us.ibm.com>,
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        Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH 04/40] xen: document Xen is using an unused bit for the
 pagetables
Message-ID: <20120704230547.GO25743@redhat.com>
References: <1340888180-15355-1-git-send-email-aarcange@redhat.com>
 <1340888180-15355-5-git-send-email-aarcange@redhat.com>
 <4FEDB8AC.4000209@redhat.com>
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On Fri, Jun 29, 2012 at 10:16:12AM -0400, Rik van Riel wrote:
> On 06/28/2012 08:55 AM, Andrea Arcangeli wrote:
> > Xen has taken over the last reserved bit available for the pagetables
> > which is set through ioremap, this documents it and makes the code
> > more readable.
> >
> > Signed-off-by: Andrea Arcangeli<aarcange@redhat.com>
> > ---
> >   arch/x86/include/asm/pgtable_types.h |   11 +++++++++--
> >   1 files changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> > index 013286a..b74cac9 100644
> > --- a/arch/x86/include/asm/pgtable_types.h
> > +++ b/arch/x86/include/asm/pgtable_types.h
> > @@ -17,7 +17,7 @@
> >   #define _PAGE_BIT_PAT		7	/* on 4KB pages */
> >   #define _PAGE_BIT_GLOBAL	8	/* Global TLB entry PPro+ */
> >   #define _PAGE_BIT_UNUSED1	9	/* available for programmer */
> > -#define _PAGE_BIT_IOMAP		10	/* flag used to indicate IO mapping */
> > +#define _PAGE_BIT_UNUSED2	10
> 
> Considering that Xen is using it, it is not really
> unused, is it?

_PAGE_BIT_UNUSED1 is used too (_PAGE_BIT_SPECIAL). Unused stands for
unused by the CPU, not by the OS. But this patch is dropped.