This sounds like you need to adjust the libvirtd apparmor profile.
Edit
/etc/apparmor.d/abstractions/libvirt-qemu
and add the following line:
/usr/bin/kvm-balloon rmix,
--
kvm memory ballooning is unusable in Lucid
https://bugs.launchpad.net/bugs/579723
You received this bug notification because you are a member of Ubuntu
Server Team, which is subscribed to libvirt in ubuntu.
--
Ubuntu-server-bugs mailing list
[email protected]
Modify settings or unsubscribe at:
https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs