https://bugs.freedesktop.org/show_bug.cgi?id=62959
--- Comment #37 from Alexandre Demers alexandre.f.demers@gmail.com --- (In reply to comment #36)
Alex, despite having your 2nd patch in, the box just crashed and rebooted. I'll revert to your first patch to see if that one still helps.
By reading bug 62997 you've reported, you may be hitting more than one bug. I had to report a couple of bugs myself about VM and DMA for Cayman.
Could you try kernel 3.9-rc7? I know a couple of patches went in there that could help you.