Without a doubt it's oil. It doesn't take much to make a cloud of smoke, maybe a drop or two, and you'd never notice it on the dip stick as being low on oil. Could be one or more valve stem seals leaking or an oil seal in the turbo. Most likely a valve stem seal though. A turbo oil seal would most likely smoke on acceleration. Pull the spark plugs one at a time and inspect them for a dark brown or black deposit on the porcelain insulator next to the center electrode. That will confirm which cylinder(s) is/are causing the problem.
Another test for valve seals is drive at a steady 60 or so mph for a minute or two. Then downshift one gear and decellerate, (foot off the throttle) to around 20mph, then accelerate and have someone behind you watch your tail pipe for a puff of smoke.