[Xen-users] VM won't boot depending on processor

[Robert Bays <robert@xxxxxxxxxx>]

Hello all,

I am trying to troubleshoot problem with our VM where it will run on 
some processor/motherboard combinations and not others.  I'm not sure 
what to try next and thought I'd ask the list for any pointers.   Here 
are the details of the setup...
xen 3.3.1
dom0: linux-2.6.26 (based on the Debian lenny packages)
domU: linux-2.6.29 with pv_ops enabled, compiled from kernel source

This setup works great on a number of different systems, but on one 
system in particular the domU fails to boot.  The domU image uses pygrub 
as the bootloader.  When the domU is started, the grub menu is ok and 
the kernel appears to start to boot, however it never does.  "xm list" 
shows the vm in the running state and it stays that way until I kill it. 
 xenctx fails to show anything useful even if I set the VM to preserve 
state on shutdown.  There is nothing in "xm dmesg" or any of the xend 
log files that is helpful.
Here is the part I'm lost on.  This dom0/domU setup has always worked in 
the past on multiple different systems.  The one system where this is 
broken is a motherboard based on an Intel Q35 chipset and an Intel Q9400 
CPU.  If I replace the CPU in the system with an Intel E8400 everything 
works.  If I put the Q9400 in a system based on an Intel 3200 chipset 
everything also works.  So it works on the Q9400 CPU and it works on the 
Q35 chipset, just not when they are in the same system.
This issue seems to have started somewhere with the linux 2.6.28-29 
kernel.  Everything works fine if the domU kernel is 2.6.27.  My next 
step is to try an isolate which kernel patch set is causing the issue, 
but before I try that I thought I'd ask if anyone has had similar 
experiences or if anyone has any other suggestions before I start a 
kernel bug hunt.
Thanks in advance.

Cheers,
Robert.

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