#StackBounty: #linux #virtual-machine #qemu #pci #virsh Unable to detach PCI device from running virtual machine ("Device is alrea…

Bounty: 500

I’m forwarding a host USB hub using this virsh config:

<hostdev mode='subsystem' type='pci' managed='yes'>
  <source>
    <address domain='0x0000' bus='0x13' slot='0x00' function='0x3'/>
  </source>
  <address type='pci' domain='0x0000' bus='0x03' slot='0x00' function='0x0'/>
</hostdev>

This works perfectly. However, I want to be able to hot attach/detach this USB hub from the VM at any time. In theory this should work:

$ virsh detach-device my-vm-name pci-root-usb-hub.xml
Device detached successfully

Ok, looks promising, however the PCI device hasn’t actually been detached. I can still see my webcam and move my mouse around inside the VM. If I run the command again:

$ virsh detach-device my-vm-name pci-root-usb-hub.xml
error: Failed to detach device from pci-root-usb-hub.xml
error: internal error: unable to execute QEMU command 'device_del': Device hostdev2 is already in the process of unplug

And it seems to be frozen there. I’m unable to actually detach the PCI device from the VM without shutting the VM down.

I’m unable to find any errors in libvirtd.log or qemu/my-vm-name.log. Is there an obvious reason why this is not working?


  • Host OS: Arch Linux (kernel 5.13.12)
  • Guest OS: Windows 10


Get this bounty!!!

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