First of all, if you notice white smoke while constant operation of the vehicle, it could be a different issue.
If there is white smoke from exhaust for few minutes after leaving a motorcycle unused for few days, then it could be wet sumping issue.
Put the motorcycle on centre stand.
Keep a tray under the engine.
Open the first strainer bolt from the front of the engine. (The strainer bolt closer to the oil pump and feeder system).
Use a 18mm socket wrench or ring spanner ( for better grip and access )
Rotate clockwise from above the engine viewpoint to loosen.
Note if there is oil dripping out of this hole. Keep a cup and contain the oil that is dripping. This may take a long time. Be patient and let the dripping come to complete stop.
Once the oil dripping stops, measure the collected oil. If there is a quantity more than 30ml, there is wet sumping occurring in your engine.
After cleaning the strainer bolt. Tighten the strainer bolt back and torque it to recommended torque value.
Use the decompressor lever and kick the kick start lever until the ammeter shows charged state.
Make it a habit to park your motorcycle with the piston at top dead centre (TDC) in the engine.
This procedure helps keep the valves closed, the big end bearing on the top position which shuts off oil siphoning to avoid excessive oil not drained by the return pump from burning.
This is a temporary fix and most users can live with this. For permanent fix a much deeper investigation is needed and a mechanic shop is advised.