I did bisect between ddffeb8c4d0331..6f0c0580b7, skipping only=
 "23d4f1f -
drm/radeon: update comments to clarify VM setup (v2)" which is a trivi=
al step
IMO. The offending commit is this:

commit 90a51a329258e3c868f6f4c1fb264ca01c590c57
Author: Christian K=C3=B6nig <deathsimple@vodafone.de>
Date:   Tue Oct 9 13:31:17 2012 +0200

    drm/radeon: allocate page tables on demand v4

    Based on Dmitries work, but splitting the code into page
    directory and page table handling makes it far more
    readable and (hopefully) more reliable.

    Allocations of page tables are made from the SA on demand,
    that should still work fine since all page tables are of
    the same size.

    Also using the fact that allocations from the SA are mostly
    continuously (except for end of buffer wraps and under very
    high memory pressure) to group updates send to the chipset
    specific code into larger chunks.

    v3: mostly a rewrite of Dmitries previous patch.
    v4: fix some typos and coding style

    Signed-off-by: Dmitry Cherkasov <Dmitrii.Cherkasov@amd.com>
    Signed-off-by: Christian K=C3=B6nig <deathsimple@vodafone.de>
    Tested-by: Michel D=C3=A4nzer <michel.daenzer@amd.com>
    Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
    Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Trying to revert this commit for 3.7-rc2 using git revert failed.