From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dave McCracken <dcm@mccr.org>
Subject: Re: [PATCH xen-unstable] Remove PSE flag from guest CR4
Date: Mon, 14 Sep 2009 12:53:38 -0500
Message-ID: <200909141253.38621.dcm@mccr.org>
References: <C6D43F08.14B08%keir.fraser@eu.citrix.com>
Mime-Version: 1.0
Content-Type: Text/Plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xensource.com>
In-Reply-To: <C6D43F08.14B08%keir.fraser@eu.citrix.com>
List-Unsubscribe: <http://lists.xensource.com/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/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: Keir Fraser <keir.fraser@eu.citrix.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>, Xen Developers List <xen-devel@lists.xensource.com>
List-Id: xen-devel@lists.xenproject.org

On Monday 14 September 2009, Keir Fraser wrote:
> If you hide PSE in CR4 and CPUID, how does the guest know it can use
> superpages?

Linux assumes it will just work.

Since hugepages in Linux are an optional feature the kernel will boot even on 
a machine that doesn't support PSE.  Applications that use hugepages will get 
a nasty error.

With the PSE bit set in CPUID Linux tries to do things like map the entire 
kernel in hugepages.

Dave McCracken