mm: fix cache mode tracking in vm_insert_mixed() breaks AMDGPU [was: Re: Latest testing with drm-next-4.9-wip and latest LLVM/mesa stack - Regression in PowerPlay/DPM on CIK?]

[Michel Dänzer]

[ Adding Dan Williams and dri-devel ]

On 14/10/16 03:28 AM, Shawn Starr wrote:
> Hello AMD folks,
> 
> I have discovered a problem in Linus master that affects AMDGPU, nobody would 
> notice this in drm-next-4.9-wip since its not in this repo.

[...]

> 87744ab3832b83ba71b931f86f9cfdb000d07da5 is the first bad commit
> commit 87744ab3832b83ba71b931f86f9cfdb000d07da5
> Author: Dan Williams <dan.j.williams at intel.com>
> Date:   Fri Oct 7 17:00:18 2016 -0700
> 
>     mm: fix cache mode tracking in vm_insert_mixed()
>     
>     vm_insert_mixed() unlike vm_insert_pfn_prot() and vmf_insert_pfn_pmd(),
>     fails to check the pgprot_t it uses for the mapping against the one
>     recorded in the memtype tracking tree.  Add the missing call to
>     track_pfn_insert() to preclude cases where incompatible aliased mappings
>     are established for a given physical address range.
>     
>     Link: http://lkml.kernel.org/r/
> 147328717909.35069.14256589123570653697.stgit at dwillia2-
> desk3.amr.corp.intel.com
>     Signed-off-by: Dan Williams <dan.j.williams at intel.com>
>     Cc: David Airlie <airlied at linux.ie>
>     Cc: Matthew Wilcox <mawilcox at microsoft.com>
>     Cc: Ross Zwisler <ross.zwisler at linux.intel.com>
>     Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
>     Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> 
> :040000 040000 7517c0019fe49c1830b5a1d81f1dc099c5aab98a 
> fd497a604a2af5995db2b8ed1e9c640bede6adf3 M      mm
> 
> 
> Removal of this patch stops graphics stalls.

Thanks for bisecting this Shawn.


> A friend of mine mentions,
> 
> "looks like a graphics thingy you depend on is requesting a mapping with a 
> not-allowed cache mode, and now you are (rightfully) getting errors?"

It would be nice to get some more specific pointers what amdgpu (or
maybe ttm, since that calls vm_insert_mixed in ttm_bo_vm_fault) might be
doing wrong.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer