I have this problem with my unsupported iommu motherboard. My solution was change my vms to pv in a dom0 terminal with qvm-prefs vm-name (sys-net,sys-firewall,personal,work) virt_mod pv
and insert ip commands in rw-config-rc.local (sorry but this mac has no slash)
In sys-net edit rw-config-rc.local
ip link set vif2.0 up
ip addr add
10.137.0.4/255.255.255.255 dev vif2.0
ip route add
10.137.0.6/255..255.255.255 dev vif2.0
then save it and change it with chmod +x
do the same In sys-firewall too and change the vif# to the one created to connect to work or personal - run ifconfig -a
change the ip. the first is the vm you are editing and the other is the vm will connects thru it.
Mos of the times it runs ok, but if you has no network, you should manually run rc.local with sudo