The approach used in installers / automation systems is to first exclude everything and then explicitly define a white list of devices that Linux should see and use. So something like
cio_ignore=all,!0.0.5000-0.5002,!0.0.4711
will significantly speed up the IPL boot process as only those four devices need to be scanned and initialized.
The drawback is that with a line like this under z/VM the console is not available. So you log into your green screen and it seems that Linux doesn't IPL as there are no messages. If you wait long enough you can log in using the normal network. The z/VM console has the number 0.0.0009, so the line above needs to be modified to
cio_ignore=all,!0.0009,!0.0.5000-0.5002,!0.0.4711
So in general for a z/VM guest cio_ignore is not really needed as the access to devices can be controlled through the z/VM user directory. For guests that should come fast up in LPAR and z/VM add the console to the white list.