Bug#691665: [squeeze] Under CentOS 6.3 as a host OS Debian kernel hangs as a guest OS (KVM-QEMU)

[Jonathan Nieder <jrnieder@gmail.com>]

Hi Zoltan,

Zoltan Frombach wrote:

> Generally kvm-qemu works. But my Debian guest OS's (Debian "squeeze"
> with 2.6.32 or 3.2.x.x kernel) won't boot up if I assign more than 4
> vcpus to the guest. What happens is the kernel starts to load then
> it freezes right where it should load the Linux agpgart module. It
> just hangs there.
[...]
> If I change the VM's config to have just 4 vcpus then it boots up
> most of the time. Sometimes it hangs with just 4 vcpus, too. When it
> hangs, it always hangs at the same point, so it is consistent.
[...]
> I've tried to blacklist the agpgart module inside my guest OS to no
> avail. Here is what I've added to the end of
> /etc/modprobe.d/blacklist.conf :
> blacklist agpgart
> blacklist intel-agp
>
> However, when the VM happens to boot up then I still see a reference
> to agpgart in dmesg (snippet):

Yes, AGP support is built in (not a module).  Luckily it's quite
possible that something else is the problem that just happens to
get initialized around the same time as AGP.

What happens if you boot in recovery mode (kernel commandline
argument "single")?

[...]
> PS: At least one other person is experiencing the exact same
> problem. He has pinned it down to the Debian kernel which runs as
> the guest. Please see his post about it:
> http://lists.centos.org/pipermail/centos-virt/2012-October/003084.html

Thanks for a clear report.

Could you try 3.5.5 or newer from experimental and let us know how it
goes?  If it's affected, we'll be better prepared to get help from
upstream, and if it isn't, we can try to find which patch fixed it and
apply the same to squeeze, so either result is a win.

Hope that helps,
Jonathan