linux-kernel - Re: [PATCH 04/40] xen: document Xen is using an unused bit for the pagetables

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Date:	Tue, 3 Jul 2012 12:45:39 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Konrad Rzeszutek Wilk <konrad@...nok.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Alex Shi <alex.shi@...el.com>,
	Mauricio Faria de Oliveira <mauricfo@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Don Morris <don.morris@...com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 04/40] xen: document Xen is using an unused bit for the
 pagetables

Hi Konrad,

On Sat, Jun 30, 2012 at 12:47:18AM -0400, Konrad Rzeszutek Wilk wrote:
> On Thu, Jun 28, 2012 at 02:55:44PM +0200, Andrea Arcangeli wrote:
> > Xen has taken over the last reserved bit available for the pagetables
> 
> Some time ago when I saw this patch I asked about it (if there is way
> to actually stop using this bit) and you mentioned it is not the last
> bit available for pagemaps. Perhaps you should alter the comment
> in this description?

As far as I can tell the comment is correct, it is the last bit
available. Simply I don't need to use it anymore. There are 3 reserved
bits, one is used by Xen, the second is used by SPECIAL the third is
used by kmemcheck.

> > which is set through ioremap, this documents it and makes the code
> 
> It actually is through ioremap, gntdev (to map another guest memory),
> and on pfns which fall in E820 on the non-RAM and gap sections.

Well I dropped this patch, there's too much other important work to
do, this is only a documentation improvement and a cleanup and I don't
need it.
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