I say you overfilled the engine with oil hence the white smoke, especially if it has just happened. If not, somebody with a hell of a lot more mechanical knowledge than I will probably know exactly but white smoke could also indicate a fucked head / gasket with water getting into places where oil should only be

Also it doesn't sound right using that much oil. If I were you the next stop should be Subaru (if under warranty still) or any of the workshops listed in the sticky.