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[qvm86-devel] Re: [Qemu-devel] kqemu in 0.7.2 no longer boots Xen

From: Anthony Liguori
Subject: [qvm86-devel] Re: [Qemu-devel] kqemu in 0.7.2 no longer boots Xen
Date: Mon, 12 Sep 2005 19:17:42 -0500
User-agent: Mozilla Thunderbird 1.0.6 (X11/20050831)

Paul Brook wrote:

[redirected to the appropriate list]

FWIW, I've also tried to get Xen running under qvm86 with no success.
The accelerator module generates an error part-way into the Linux boot
sequence (right after disk probing).

dmesg shows that shadow faulting the GDT is failing but that's occuring
a bit before it bails out (according to the timestamps).

Hmm, interesting. This implies it's running ring3 code before the guest kernel finishes booting. I wonder if it's using the sgdt instruction. This will give incorrect results under qvm86.
The guest kernel should be running in ring1. I'm not familiar enough with the qvm86 code to know how that's going to affect things. AFAIK, the guest kernel will be using sgdt and friends since these can be done safely from a lower privilege.

I can provide a script that can take a built Xen tree and launchs qemu
with Xen automatically (you could provide an empty disk since it dies
long before it mounts the disk).  It's not as simple as just passing a
-kernel because Xen needs to be booted via multiboot.

I can't promise anything, but a script would be helpful.
Of course, I'll eventually get around to trying to get it to work myself. Still trying to get a grasp of the codebases.


You have two options, you can grab a source tree of xen-unstable[1] and after doing a make, invoke like:

qemu-xen /path/to/source/tree

Or you can install mbootpack[2] and grab a binary snapshot of xen-unstable[3] and invoke like:

qemu-xen --binary /path/to/snap/shot

In both cases, you'll need to create an empty base.img device.

[1] http://www.cl.cam.ac.uk/Research/SRG/netos/xen/downloads/xen-unstable-src.tgz
[2] http://www.freshmeat.net/projects/mbootpack/
[3] http://www.cl.cam.ac.uk/Research/SRG/netos/xen/downloads/xen-unstable-install-x86_32.tgz


Anthony Liguori


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