I've looked through this thread and can't find the answer - is yours an auto? If so, read on - if yours is a manual, just forget this post altogether!
Quickly take a note of how many km on your odometer, and subtract however much km you've done since it stopped smoking (so if your odo reads 110,590 and you just did 120km, the magic number is 110,470). Now, add 200 to that number.
When your odo passes this magic number, start checking your mirrors. If you notice clouds (and I mean CLOUDS) of whitish/greyish "smoke", there's an excellent chance your DPF is not regenerating properly. My own car did this. In fact, I was stopped by the Highway Patrol for a random breast test and it started billowing clouds - I shut the engine down to stop it, and noticed that as I drove away the smoke was gone! It did return later.
Turns out my DPF sensors had packed it in. A replacement set from
@auggie on this forum fixed it right up, no dramas, just plug and play, didn't have to do anything else and the car's been perfect ever since.