On 09/15/2015 05:35 PM, M A Young wrote:
> On Tue, 15 Sep 2015, Cole Robinson wrote:
>> Anyone know how to get fedora + xen running in a KVM VM? I'd like to be able
>> to do basic xen/libxl/libvirt testing without needed to reboot a physical 
>> machine.
>> Trying with F23 AMD host, F22+xen L1, trying to boot into xen in the L1 VM
>> just reboots very soon after trying to boot the kernel. Tried disabling all
>> virtio for L1 VM, disabling virt extensions for the L1 VM, but it didn't seem
>> to change anything. Unfortunately the messages scroll by so quickly I can't
>> tell what's happening right before it reboots, and all efforts to convince it
>> to print more debugging haven't worked.
>> FWIW this does work with rhel5+xen L1, but that's a world away at this point.
>> So anyone know if it's even possible? Is there a trick to it? If not,
>> suggestions on getting more debug output from xen + grub2?
> It works for me after a basic and probably sub-optimal install, as follows
> * qemu-kvm -cdrom Fedora-Server-DVD-x86_64-22.iso -m 1024 -hda kvm.img
> * do a minimal install
> * after reboot dnf install xen xen-hypervisor
> * select "Fedora, with Xen hypervisor" in the boot menu

Thanks, the minimal command line worked for me. It allowed me to track it back
and and find the culprit.

It comes down the -cpu value; the default qemu64 works, but any Opteron_* or
-cpu host do not work. I had played around with this originally thinking maybe
it was a nested virt issue, and tried Opteron_G1 which lacks svm, but never
actually tried the default qemu64 cpu...

So this doesn't work:

  $ qemu-kvm -m 1024 -hda kvm.img -cpu Opteron_G1

However this does:

  $ qemu-kvm -m 1024 -hda kvm.img -cpu Opteron_G1,family=6

qemu64 uses family=6, but Opteron_G1 uses family=15. I see there's some bits
of qemu that trigger off family>6 regarding setting some bits about MCE, but I
tried disabling those in the code and things still errored. More data points:

- TCG works fine for every combo I tried
- cpu qemu64,family=15 fails
- None of this affects my intel host, all these work fine: -cpu host, -cpu
Opteron_G1, -cpu qemu64, -cpu qemu64,family=15

So given all that, anyone have a suggestion of whether this is a KVM or Xen bug?

> If you need more debugging, boot without xen, and edit the grub.cfg file,
> adding console=com1 after xen.gz and replacing rhgb quiet with 
> console=hvc0 in the 'Fedora, with Xen hypervisor' section, then boot kvm 
> with -serial eg. -serial file:boot.log which should give you xen logging 
> after grub has finished.

Unfortunately I couldn't get anything else extra out of xen using any of these
options or the ones Major recommended... in fact I couldn't get anything to
the serial console at all. console=con1 would seem to redirect messages since
they wouldn't show up on the graphical display, but nothing went to the serial
log. Maybe I'm missing something...

sync_console gives an extra message but that's all I could see. Is
console=hvc0 correct for a KVM guest, or is that only going to work for
xen-on-xen ? I tried console=ttyS0 as well but it didn't make a difference

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