Comment 20 for bug 1677398

I have the same problem using raw lvm logical volumes as disk on Ubuntu 18.04.
When i try to start a vm with virt-manager qemu says Permission denied on device.

The lvm uses device mapper to map the logical volumes so i need to handle devices like

brw-rw---- 1 libvirt-qemu kvm 253, 4 mar 17 13:24 /dev/dm-4

After a bunch of failure attempts to start the vm machine, the following steps was successful:

I run the aa-logprof (apparmor-utils package) util to update the apparmor profiles using the syslog, and
i add the following line in /etc/apparmor.d/abstractions/libvirt-qemu

...
  /dev/dm* krw,

just before the /dev/net/tun rw, line.

If the line already exists just replace "rw" with "krw" to permit file lock operations.

Now it seems vm runs well again.