sve dok

1. as long as
   Možeš da ostaneš sve dok ti treba. — You can stay as long as you need.
   Sve dok plaćaš na vreme, nema problema. — As long as you pay on time, there's no problem.
2. (with ne) until
   Čekaću sve dok ne dođeš. — I'll wait until you come.
   Mešajte sve dok se šećer ne istopi. — Stir until the sugar dissolves.

In the meaning "until" a perfective verb with ne is usually used; this ne does not make the meaning negative.