[libvirt] cgroup limits only affect kvm guest under certain conditions

[Dominik Klein]

> Did you just echo the main qemu-kvm PID, or did you also
> add the PIDs of every thread too ? From this description
> of the problem, I'd guess you've only confined the main
> process thread and thus the I/O & VCPU threads are not
> confined.

That was indeed correct. I was mislead by the fact that no child
_processes_ were shown in ps.

Once I added /proc/<qemu-pid>/tasks/* to tasks, it worked even when
libvirt started the process.

Thank you very much!
Dominik