There seems to be a problem with the apparmor profile of libvirt (see bug #54579). After adding the line
/dev/ttyS* rw,
to /etc/apparmor.d/abstractions/libvirt-qemu and reloading the profile it worked for me.
There seems to be a problem with the apparmor profile of libvirt (see bug #54579). After adding the line
/dev/ttyS* rw,
to /etc/apparmor. d/abstractions/ libvirt- qemu and reloading the profile it worked for me.