Hello,
I'm also seeing this exact same problem. I've posted on xen-users, but did 
not get an answer. Venkat seems to be experiencing the same problem as me. I 
have the latest BIOS for my motherboard DQ35JO. (BIOS ver 933) I'm running a 
Q6600 as well. It hangs at "Brought up 4 CPUs." I've tried all sorts of 
combinations of Xen versions and kernels to get this working. And, yes, VT and 
VT-d are enabled in my BIOS.
1) CentOS 5.2 SRPMS compiled with Xen 3.2.1. 
Adding pci=nommconf does not get it to boot.
2) Mercurial Xen-3.2-testing. Here, after adding pci=nommconf, I get:
(XEN) [VT-D]dmar.c:441: RMRR is incorrect.
(XEN) Failed to parse ACPI 
DMAR.  Disabling VT-d.
(XEN) [VT-D]ACPI DMAR:No DMAR devices found
3) Mercurial Xen-unstable, I get "I/O Virtualisation disabled" I can't find 
any reason why this is the case. VT-D is not enabled.
I would really like to find the cause for this. I don't know if this is a 
BIOS bug or what. This board is supposedly supported on Xen per the VT-D wiki. 
Other people seem to have the same problem as me:
http://forums12.itrc.hp.com/service/forums/bizsupport/questionanswer.do?admit=109447627+1217898320366+28353475&threadId=1234588
Thanks for any and all help,
-Bryan
  
The BIOS version I use may be not the exact one as yours. I mean I expect 
you're
not using a very old BIOS. :-) 
How about trying the xen 3.2.2-rc2 and the latest xen-unstable first? There 
are some VT-d bug fixes between 3.2.1 (you're using it) and 3.2.2-rc2. 
Thanks, 
-- Dexuan 
________________________________ 
From: Kumar, Venkat [mailto:Venkat.Kumar@xxxxxxx] Sent: 
2008年8月5日 14:37 To: Cui, Dexuan; xen-devel@xxxxxxxxxxxxxxxxxxx 
Subject: RE: [Xen-devel] Xen-3.2.1 VT-d Support (NOT SURE WHETHER IT'S A 
BUG
OR...) 
If you don't mind can you send me the BIOS version you are using? 
Thx, 
Venkat 
================================ 
Venkata Kumar Duvvuru, 
LSI Engenio, 
Adv. Development, 
Bangalore. 
Mob: +91-9880318542 
Off : +91-80-41978700 ( Extn : 3544 ) 
________________________________ 
From: Cui, Dexuan [mailto:dexuan.cui@xxxxxxxxx] Sent: 
Tuesday, August 05, 2008 12:03 PM To: Kumar, Venkat; xen-devel@xxxxxxxxxxxxxxxxxxx 
Subject: RE: [Xen-devel] Xen-3.2.1 VT-d Support (NOT SURE WHETHER IT'S A 
BUG
OR...) 
Hi Venkat, 
Can you confirm you're using the latest BIOS? Can you try the xen 3.2.2-rc2 
and
the latest xen-unstable on the same host? 
I have the similar host. Xen 3.2.2-rc2 and the latest xen-unstable both 
work
well on it. 
Thanks, 
-- Dexuan 
________________________________ 
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] 
On Behalf Of Kumar, Venkat Sent: 2008年8月5日 12:21 To: xen-devel@xxxxxxxxxxxxxxxxxxx 
Subject: [Xen-devel] Xen-3.2.1 VT-d Support (NOT SURE WHETHER IT'S A BUG 
OR...) 
After building Xen-3.2.1 I could successfully boot into it if I avoid 
giving
vtd=1 as the boot parameter. 
If I pass vtd=1 as the boot parameter to xen, the system hangs while booting. 
The system hangs after the following messages 
============================ 
Boot messages 
[XEN]….. 
[Xen] Brought up 2 CPUs... 
========================= 
My chipset DQ35 series is having VT-d support and is enabled in the 
BIOS as
well. 
My domain0 is CentOS-5.2(2.6.18.8-xen). 
Is this a possible bug or some thing else?? 
Any Idea?? 
Thx,