CS-P 220 Feathering Propellers
(a) Feathering Propellers must be designed to feather from all conditions in flight, while taking into account likely wear and leakage. Feathering and unfeathering limitations must be documented in the appropriate manual(s).
(b) Propeller pitch control systems that use engine oil to feather must incorporate a method to allow the Propeller to feather if the engine oil system fails.
(c) Feathering Propellers must be designed to be capable of unfeathering after being feathered for the maximum expected diversion time at the minimum declared steady state outside air temperature.
(d) Where there is a minimum Engine/Propeller rotational speed and/or associated aircraft speed below which Propeller feathering cannot be accomplished, the Propeller type-certificate data sheet must be endorsed
accordingly.
(My italicization)
This is usually done through a separate feathering pump which draws oil from a part of the sump which is not accessible to the engine oil pump.