Most Generational GC's (including Hotspots, which is the origin of Azul's JVM) will have the JIT insert a write barriers for all pointer sets. This is to keep track of cross generational references (so you don't have to scan the entire heap).

The hard part has always been dealing with reads, (which are much more common and expensive to put a software barrier around), and Azul has quite brilliantly figured a way to handle this both in their specialized hardware, and now their VM.