Originally Posted by Rcon
Your best bet is to spray it - if it's loose and you try to roll it the texture will likely peel off as you roll.
A good bonding primer and a couple of finish coats by spray application should do it.
Rcon is right; however, if you don't have access to a sprayer, roll the places that are firmly adhered and use your brush where it seems to be loose. If you're using a flat paint you won't even notice any brush marks. If some of that texture comes off the ceiling, you're gonna have trouble matching it if you go to repair it.