If it's white, it's coolant, not oil. So it isn't the valve stem seals or the piston rings.
By any chance was the engine overheated?
Valve stem seal smoke is from oil getting down the valve stem. The amount is so small that it typically doesn't cause smoke when the engine is running. After the engine is shut off, oil goes from the top of the engine where it has been pumped down wherever gravity carries it. If the valve stem seals are shot (hard, cracked), oil seeps down the valve stems into the combustion chamber and "pools". When you fire it up the next time, there is enough of a concentration to produce visible smoke.