RE: [Xen-users] HVMloader boots cdrom but get a blank screen.

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Edward Ing
> Sent: 18 December 2006 15:51
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] HVMloader boots cdrom but get a blank screen.
> 
> Hi,
> 
> I am trying to install several OSes using HVMloader/cdrom booting
> method.
> When I look at the console I see that the cdrom boot takes place, very
> quickly, however the domU boots into a blank/black screen when
> installing Ubuntu, Kbuntu. It boots into a console, but I can see that
> there is a boot loader error when booting to a FreeBSD cdrom. 
> Windows XP
> works fine.

Try using a "text-only" boot. I know for a fact that some of the
graphics boot routines use "tricky stuff" like "big real-mode", which
particularly on Intel platforms that don't have "real mode
virtualization" in hardware, it can be tricky to make it work. 

FreeBSD, I think, uses segments with base != 0 in protected mode, which
can also be a cause for problems. 

> 
> I don't think that there is much I can do about this. It is 
> the problem
> of distro boot cdrom. But generally, can anyone explain what is the
> problem with distros that run into this problem.

Generically, I would say that the problem is with either the
load-process (where the initial boot-loader loads the installation
kernel) or with graphical boot routines, depending on how far you get
into the boot/install process. 

The problem here is that the processor starts out in real mode, and
that's the only mode that supports BIOS for the purpose of reading the
disk (CD-ROM or otherwise). Since real-mode is restricted to 1MB of RAM,
it can be hard to fit everything into that limited amount of memory - so
the code-writer will have a few choices::
- switch to protected mode, which means no BIOS -> must have drivers
capable of reading the disk by itself. 

- switching back and forth between real-mode and protected-mode. Not too
bad, except it's a little bit of work to be done each switch, and you
can't (practically) use any code from one side of Prot/Real-mode fence
in the other mode. 

- Use "big-real-mode", which is done by switching to protected mode,
setting up a segment register that is not used by BIOS to access "all"
memory, and return to real mode. 

Unfortunately, if the processor doesn't support real mode
virtualization, then the big-real-mode will be a bit of a problem too,
since the Virtual 8086 mode that the processor is in for HVM "real-mode"
doesn't support certain operations such as going to protected mode and
back again and retaining the segment registers values!

This is of course just a GUESS on what the problem is. 

--
Mats
> 
> I am about to try SUSE.
> 
> 
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