From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <jbeulich@novell.com>
Subject: mapping of memory below 16Mb
Date: Thu, 24 Jan 2008 15:15:49 +0000
Message-ID: <4798B9B5.76E4.0078.0@novell.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: quoted-printable
Return-path: <xen-devel-bounces@lists.xensource.com>
Content-Disposition: inline
List-Unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: xen-devel@lists.xensource.com
List-Id: xen-devel@lists.xenproject.org

One point I got a little surprised about while doing the 1Gb page support:
The 1:1 mapping of the low 16 Mb (and most significantly the first Mb)
created at boot time is being retained permanently. Shouldn't Xen be
following the E820 map also for this memory range (by either not
mapping non-RAM at all or at best mapping them UC/WP)?

The WP attribute raises another question: Are there any plans to make
Xen use PAT rather than (relying on) MTRRs? Linux folks seem to be
finally getting closer to this, too, so even virtual PAT support may be
needed in not too distant future...

Jan