Since I upgraded my deployment from Havana to Icehouse, I can no longer launch VMs when libvirt's virt_type is set to "kvm" (in compute node's /etc/nova/nova-compute.conf). However, with if virt_type is set to "qemu" it works perfectly. Back in Havana I've always used "kvm".
The machines and operating systems are unchanged since Havana, and the OS is Ubuntu 12.04.4 LTS.
I can see the qemu-system-x86_64 process taking up 100% CPU. I can't find any relevant logs to further understand what's happening.
I am using Neutron for networking, which is also working properly.
Here is the Compute node's nova.conf: http://paste.openstack.org/show/76662/
Compute node's nova-compute.conf: http://paste.openstack.org/show/76663/
Controller node's nova.conf: http://paste.openstack.org/show/76664/
Compute's libvirt instance file: /etc/libvirt/qemu/instance-00000033.xml: http://paste.openstack.org/show/76674/
My bug report concerning this has recently been confirmed: https://bugs.launchpad.net/nova/+bug/... .