On 17 October 2016 at 04:41, Marek Olšák <mar...@gmail.com> wrote:
> On Fri, Oct 14, 2016 at 3:33 AM, Michel Dänzer <mic...@daenzer.net> wrote:
>> [ 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
>>> 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.willi...@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/
>>> Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
>>> Cc: David Airlie <airl...@linux.ie>
>>> Cc: Matthew Wilcox <mawil...@microsoft.com>
>>> Cc: Ross Zwisler <ross.zwis...@linux.intel.com>
>>> Signed-off-by: Andrew Morton <a...@linux-foundation.org>
>>> Signed-off-by: Linus Torvalds <torva...@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.
* We'd like to use VM_PFNMAP on shared mappings, where
* (vma->vm_flags & VM_SHARED) != 0, for performance reasons,
* but for some reason VM_PFNMAP + x86 PAT + write-combine is very
* bad for performance. Until that has been sorted out, use
* VM_MIXEDMAP on all mappings. See freedesktop.org bug #75719
vma->vm_flags |= VM_MIXEDMAP;
We have that comment in the ttm code, which to me implies that mixed is
doing the right thing now, but that is slow, as the interface we
should be using.
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