[libvirt] Host device assignment driver name vfio/ kvm

Hi, I was testing Host device assignment in OpenStack environment where the driver name is vfio or kvm. My setup is as follow: 1. Fedora 21 2. Libvirt 1.3.0 which I compiled 3. OpenStack master I have also other setups with older Libvirt version and the same OpenStack environment. I notice that on my fedora environment the driver name is vfio were in my old environment the driver name is kvm. According to Libvirt documentation default is "vfio" on systems where the VFIO driver is available and loaded, see [1] I remove the vfio modules by removing vfio, vfio_iommu_type1, vfio_pci but when I boot a vm the drive name is vfio How can change the driver name to be kvm? Another thing that I encounter is an error when suspending VM (in OpenStack environment) when the driver name is vfio. In such case I am getting the following error from Libvirt: 2016-03-28 11:42:59.527 1966 ERROR oslo_messaging.rpc.dispatcher File "/usr/lib64/python2.7/site-packages/libvirt.py", line 560, in attachDeviceFlags 2016-03-28 11:42:59.527 1966 ERROR oslo_messaging.rpc.dispatcher if ret == -1: raise libvirtError ('virDomainAttachDeviceFlags() failed', dom=self) 2016-03-28 11:42:59.527 1966 ERROR oslo_messaging.rpc.dispatcher libvirtError: internal error: unable to execute QEMU command 'device_add': Device initialization failed. I would appreciate for some pointers on what can cause this issue. [1] https://libvirt.org/formatdomain.html#elementsHostDev