(In reply to comment #35)
> 
> Wait: according to http://dri.freedesktop.org/wiki/GART/ the GART seems to
> enable the video card to access the computer's memory, not the other way
> around.  So I don't see how this is relevant: we're getting a crash in a CPU
> instruction that is trying to access the video card's memory.

GART and VRAM are separate.  As I said in comment 12, I though there may have
been two issues at play at first, but upon further debugging, it appears to
just be the vram window.