port-xen/46634: X does not work anymore with Xen (DOM0, amd64)

[Pierre Pronchery <pierre.pronchery%duekin.com@localhost>]

>Number:         46634
>Category:       port-xen
>Synopsis:       X does not work anymore with Xen (DOM0, amd64)
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    port-xen-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jun 27 19:00:00 +0000 2012
>Originator:     Pierre Pronchery <pierre.pronchery%duekin.com@localhost>
>Release:        NetBSD 6.0_BETA2
>Organization:
DUEKIN Consulting
>Environment:
System: NetBSD syn.defora.rom 6.0_BETA2 NetBSD 6.0_BETA2 (XEN3_DOM0) #6: Wed 
Jun 27 15:59:01 CEST 2012 
khorben%kwarx.defora.lan@localhost:/home/amd64/obj/sys/arch/amd64/compile/XEN3_DOM0
 amd64
Architecture: x86_64
Machine: amd64
>Description:
As observed by a few other users already (on port-xen@), Xorg no longer
works when running a NetBSD DOM0 kernel for Xen. The log shows this:

=== BEGIN PASTE ===
(II) RADEONHD(0): Getting BIOS copy from legacy VBIOS location
(EE) RADEONHD(0): Cannot allocate 0 bytes of memory for BIOS image
(EE) RADEONHD(0): Cannot allocate 0 bytes of memory for BIOS image
(II) RADEONHD(0): Query for AtomBIOS Init: failed
[...]
(EE) Screen(s) found, but none have a usable configuration.

Fatal server error:
no screens found
=== END PASTE ===

The same happens with both the vesa and radeonhd drivers on this machine
(Lenovo ThinkPad T60 2007).

After reading the source code for xf86-video-vesa, xf86-video-radeonhd
and xorg-server, it seems that the Video BIOS is no longer available at
the expected address.

Dumping 64KB of memory at 0xc0000 results in all zeros, whereas I would
be expecting a copy of the Video BIOS to be found there (as confirmed
with a GENERIC kernel).

>How-To-Repeat:
Install, configure and attempt to run Xorg on NetBSD/amd64 with a
XEN3_DOM0 kernel.

>Fix:
Unknown.