Is there anything else I could try to help track this down?

I tried running the game with R600_DEBUG=nodma and while that seemed to fix the
issue at first, I still got a lockup after a couple of runs. Perhaps nodma just
made the lockup less likely by slowing things down (although perf was not
*that* different).

Btw, jaycee1980 in #radeon seemed open to providing AMD Mesa devs keys to
Virtual Programming games, so you could try to reproduce this on your end as
well.