I get this error with xen 4.1:
(XEN) ****************************************
(XEN) Panic on CPU 0:
(XEN) FATAL PAGE FAULT
(XEN) [error_code=0000]
(XEN) Faulting linear address: 0000000000000000
(XEN) ****************************************

After disabling iommu it gets past that point, gets to the login.
At this point, tty7 and above is busy doing nothing, they don't work.
Sometimes tty0 gets busy and won't finish loading up to the login prompt.
However tty1-6 work.
Startx not working, wth..., gdm3 start is working though, even though I prefer kde plasma lol.
When trying gdm3, it loads up a bit, goes to a blank screen and just sits there like tty7+.

I'm using kali linux, which has given me nothing but probs.
Backtrack 5r3 was better in my opinion, less bugs, and much easier to setup.

I got many thing working again, but of all things, I have to install deb packs from the freakin cmd line.
Apt-get server list thingy had to be redone to get it to download anything at all...
I had to get rid of that darned nouveau thing, that made it a pain to get the real drivers working.
I could go on and on lol.

I'm still dl'ing ubuntu and debian.
From my understanding though they already have that nouveau crap installed :\.
I need to roll my own again like way back in the day, but I need good experience with a working os 1st.

My board is missing the acpi iommu rom as well.
Kind of ticks me off because that feature is something I wanted and figured I was getting when I bought this board+cpu a few years back now.
It's no wonder that I never got any pass through working on a windows baised os vm.
Real shame too, 6 core's, not really put to use when it comes to the os it's self.

Ohwell, at least eventually, hopefully, I'll get xen wokring to play with, even without passthrough.
Just without it it won't be the same, I won't beable to use that setup, just play with it as a toy.
I got this grid gpu and nothing to use it with lol, thanks asus ^^ :\.
Hopefully since the setting for it is in the bios, just no rom, maybe it'll be an easy fix by just inserting the module form another board.
But then again, being apart of acpi, it might be a real pain to insert and get it hooked up right in the bios.
This is like the sli mods, except it's a new thing to mess with .

But anyways I'm in the same situation as the thread op.
I want to get a hypervisor working with passthrough, and in the end, my grid gpu working.
So each os can share the same gpu.