Hi all I just encountered a problem in libvirt while was trying to attach and detach a sr-iov vf to my VM The version of my libvirt is 1.1.1-0ubuntu8.5 I tried to attach the device using following xml <interface type='hostdev' managed='yes'> <mac address='5c:01:fd:12:34:58'/> <source> <address type='pci' domain='0x0000' bus='0x04' slot='0x01' function='0x1'/> </source> </interface> When i attached device it worked properly and i managed to ping another host. virsh # attach-device t5 1.xml Device attached successfully But when i detached it still i had network traffic in my VM but libvirt (virsh) said that virsh # detach-device t5 1.xml Device detached successfully The next time i tried to attach it libvirt said that virsh # attach-device t5 1.xml error: Failed to attach device from 1.xml error: Requested operation is not valid: PCI device 0000:04:01.1 is in use by domain t5 I tried it with different VMs and different guest OSs that the same happend. The same action was done with another host running libvirt version Installed: 1.0.2-0ubuntu11.13.04.5~cloud1 Candidate: 1.0.2-0ubuntu11.13.04.5~cloud1 and it worked pretty OK. No problem. Do you have any idea what is wrong? More information: Kernel : 3.8.0-37-generic /etc/libvirt/qemu.conf : security_driver = "none” root@compute01:~# ethtool -i eth5 driver: bnx2x version: 1.78.58 firmware-version: bc 7.4.22 phy 1.34 bus-info: 0000:04:00.1 supports-statistics: yes supports-test: yes supports-eeprom-access: yes supports-register-dump: yes