On Mon, Jan 25, 2016 at 4:46 AM, Julian Margetson <runaway@candw.ms> wrote:
> Oops starting Xorg with kernel 4.5-rc1 on Acube Sam460ex amcc460ex powerpc
> motherboard.
>
> ======================================================================================================================
> 01c8f1c44b83a0825b573e7c723b033cece37b86 is the first bad commit
> commit 01c8f1c44b83a0825b573e7c723b033cece37b86
> Author: Dan Williams <dan.j.williams@intel.com>
> Date:   Fri Jan 15 16:56:40 2016 -0800
>
>     mm, dax, gpu: convert vm_insert_mixed to pfn_t
>
>     Convert the raw unsigned long 'pfn' argument to pfn_t for the purpose of
>     evaluating the PFN_MAP and PFN_DEV flags.  When both are set it triggers
>     _PAGE_DEVMAP to be set in the resulting pte.
>
>     There are no functional changes to the gpu drivers as a result of this
>     conversion.
>
>     Signed-off-by: Dan Williams <dan.j.williams@intel.com>
>     Cc: Dave Hansen <dave@sr71.net>
>     Cc: David Airlie <airlied@linux.ie>
>     Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
>
> :040000 040000 dc71b6dc188dea4b6ce95f5fd1e4e73cc3663cbe
> 8a745459a14cd2a6f4e1c71fda3e54333d023f43 M arch
> :040000 040000 9e8103b65698f677e17becdac53914ca029a6197
> f656e15bffef4ea8c848176a79eb50a071ec323e M drivers
> :040000 040000 3ffc222d7e0f1067772798d08777aeb54136026e
> e2b423f85aaaf0cb25d48d1e15771fc5bddf7981 M fs
> :040000 040000 392d2dea8185ba8f0d1c101782831ceed9aa9812
> 9e3001b04052daa1b3204b6f2a6e26138a4ed7dd M include
> :040000 040000 f81d8cfe3052b7259b75a58656a65efdaad40284
> 969d0ff262020f27a695172ce89ae5f6088e8d44 M mm
>

Hmm, this commit could only cause a behavior change if it modifies the
value of the pfn as seen by insert_pfn().  Can you try the attached
debug patch to see if that assumption is being violated?