(In reply to comment #7)
> Created attachment 71883 [details]
> dmesg with drm-fixes-3.8
> 
> The dmesg message changed after merging in drm-fixes-3.8:
> 
> [drm:evergreen_vm_reg_valid] *ERROR* Invalid register 0x8040 in CS

That's a different bug.  Please file a new one for that.  what you are seeing
is due to a change in mesa:
http://cgit.freedesktop.org/mesa/mesa/commit/?id=24b1206ab2dcd506aaac3ef656aebc8bc20cd27a