This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


RE: [Xen-devel] [PATCH 2/3] x86: real mode support: get EDD info

To: "Keir Fraser" <keir@xxxxxxxxxxxxx>, "Jan Beulich" <jbeulich@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-devel] [PATCH 2/3] x86: real mode support: get EDD info
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Fri, 2 Mar 2007 12:49:53 +0100
Delivery-date: Fri, 02 Mar 2007 03:50:20 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <C20DBC9D.A7BF%keir@xxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcdcvvGVMAXExsiyEduwRgAX8io7RQAAXtTA
Thread-topic: [Xen-devel] [PATCH 2/3] x86: real mode support: get EDD info

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Keir Fraser
> Sent: 02 March 2007 11:36
> To: Jan Beulich; xen-devel@xxxxxxxxxxxxxxxxxxx; Keir Fraser
> Subject: Re: [Xen-devel] [PATCH 2/3] x86: real mode support: 
> get EDD info
> On 2/3/07 11:26, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
> > Possible, but especially on x86-64 undesirable in my opinion.
> It's certainly more of a pain to make the mode switch, but 
> not impossible by
> any means.

It's not that much harder as long as you have some region of (below 1MB
is probably best) memory that is 1:1 mapped that you can put the code
into. Jump to a 32-bit segment (i.e. cs.attr.large-mode = 0) in low
memory, turn off LME in EFER and PG in CR0, then turn off PE in CR0 and
you're in real-mode. Of course to make the environment work for
real-mode, there's a whole bunch of other stuff that needs to be done
(interrupt vector table at address zero for example), but that should be
the same whether you run 64- or 32-bit code in the first place. 

> > Also, I'll want
> > the base real mode stuff in anyway (regardless of EDD/EDID) 
> in order to
> > be able to set up a VESA frame buffer mode for the console. 
> This clearly
> > should be done by Xen in order to ensure it knows how to access the
> > console in case it is allowed access past dom0 creation.
> Oh yes, we definitely want the mode-switching code in Xen. No 
> doubt about
> that. The question is whether we pull in the EDD/EDID stuff 
> as well. The
> fact that the data format is BIOS-defined does make the 
> current approach
> plausible if not particularly tasteful architecturally 
> speaking (but what
> BIOS stuff is? :-).
>  -- Keir
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel

Xen-devel mailing list

<Prev in Thread] Current Thread [Next in Thread>