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

To: <xen-devel@xxxxxxxxxxxxxxxxxxx>,"Keir Fraser" <keir@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 2/3] x86: real mode support: get EDD info
From: "Jan Beulich" <jbeulich@xxxxxxxxxx>
Date: Fri, 02 Mar 2007 11:26:10 +0000
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>>> Keir Fraser <keir@xxxxxxxxxxxxx> 02.03.07 12:15 >>>
>On 2/3/07 10:32, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>> Obtain EDD info from BIOS and pass it up to Dom0.
>What data format are the EDD/EDID buffers filled with? The format is not
>defined in the public headers. Is it simply whatever Linux happens to be
>using internally?

No, this is the BIOS format. Linux uses this directly. I specifically (based
on past comment from you) avoided introducing Linux specifics.

>I am still interested in trying out an interface to let dom0 request code to
>be run in various modes and on various CPUs. This would be attractive in
>this case, assuming that these BIOS calls could be made later than very
>early bootstrap, as it would avoid piling code into Xen, and assumptions
>about info data formats, just because of the environment that the
>interrogating code needs to be executed in. No doubt it is a larger initial
>amount of engineering effort up front though. Also I'm not sure if there
>would be any subtle gotchas to running this skanky BIOS code later in the
>boot sequence (I'd be optimistic that it'd just work though).

Possible, but especially on x86-64 undesirable in my opinion. 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.


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