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RE: [Xen-users] How do I find out why Dom0 crashes on guest startup?

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Subject: RE: [Xen-users] How do I find out why Dom0 crashes on guest startup?
From: "Schober Walter" <Walter.Schober@xxxxxxxxx>
Date: Fri, 18 May 2007 14:10:25 +0200
Cc: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
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Thread-topic: [Xen-users] How do I find out why Dom0 crashes on guest startup?
1. apic=0, vcpus=4     OK, no crash

2. apic=1, vcpus=1     OK, no crash

3. apic=1, vcpus=2     OK (?!?!?) But:
(XEN) This hvm_vlapic is for P4, no work for De-assert init
(XEN) (file=hvm.c, line=665) AP 1 bringup suceeded.
(XEN) vmx_do_launch(): GUEST_CR3<=00fbd7a0, HOST_CR3<=cc3ae000
(XEN) (GUEST: 4) Start AP 1 from 00006000 ...
(XEN) (GUEST: 4) Starting emulated 16-bit real-mode: ip=0600:0000

4. apic=1, vcpus=4     NOK, but no crash anymore ?!?!?
A lot of 
(XEN) <ioapic_inj_irq> error delivery mode 7
and on the guest:
..MP-BIOS bug: 8254 timer not connected to IO-APIC
Kenrel panic - not syncing: IO-APIC + timer doesn't work! Try using the
noapic kernel parameter

5. apic=1, vcpus=4, 'xm create' right after reboot      NOK, Dom0
crashes as before

6. starting at least one another VM with apic=0 or commented out apic ->
See 3. + 4., but no Dom0 crash.

=> Dom0 crashes only, if the hvm wasn't started with apic=0 once before.

That brings me back to time when I installed that VM: Installation was
possible only with vcpus=1 (stale after Centos 5 Install Screen). After
that I set vcpus=4 and rebootet the VM.

On Wednesday I had to reboot the Dom0 for that HP management thing and
started the VM the first time directly with apic=1, vcpus=4 causing the
crash. So it had nothing to do with the HP drivers nor QEMU package.

I guess, I have to wait for a fix in the Xen kernel or maybe try to
compile my own 3.0.4.

Thanks, Mats for you help!

-----Original Message-----
From: Petersson, Mats [mailto:Mats.Petersson@xxxxxxx] 
Sent: Friday, May 18, 2007 1:22 PM
To: Schober Walter; xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] How do I find out why Dom0 crashes on guest

[snip big log]
> (XEN) Xen call trace:
> (XEN)    [<ffff830000142da7>] vlapic_range+0x7/0x30

So, the code here does very few things (at least in the current version,
but I doubt that the older code is MUCH different). This in turn means
that it's pretty easy to determine what could be wrong:
1. VCPU = NULL - quite likely, as it's one of the first steps. 
2. vlapic field in vcpu = NULL - even more likely. 

I'd try running your guest with "apic=0" to see if that makes any
difference. [That will of course screw up SMP on your guest, but at
least it will hopefully tell us if it's APIC that is a problem or not]

I doubt that having installed a newer QEMU would make any difference. 


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