[PATCH 0/9] Emulated coherent graphics memory v2

Thomas Hellstrom thellstrom at vmware.com
Wed Apr 24 12:00:09 UTC 2019

Graphics APIs like OpenGL 4.4 and Vulkan require the graphics driver
to provide coherent graphics memory, meaning that the GPU sees any
content written to the coherent memory on the next GPU operation that
touches that memory, and the CPU sees any content written by the GPU
to that memory immediately after any fence object trailing the GPU
operation has signaled.

Paravirtual drivers that otherwise require explicit synchronization
needs to do this by hooking up dirty tracking to pagefault handlers
and buffer object validation. This is a first attempt to do that for
the vmwgfx driver.

The mm patches has been out for RFC. I think I have addressed all the
feedback I got, except a possible softdirty breakage. But although the
dirty-tracking and softdirty may write-protect PTEs both care about,
that shouldn't really cause any operation interference. In particular
since we use the hardware dirty PTE bits and softdirty uses other PTE bits.

For the TTM changes they are hopefully in line with the long-term
strategy of making helpers out of what's left of TTM.

The code has been tested and excercised by a tailored version of mesa
where we disable all explicit synchronization and assume graphics memory
is coherent. The performance loss varies of course; a typical number is
around 5%.

Any feedback greatly appreciated.

Changes v1-v2:
- Addressed a number of typos and formatting issues.
- Added a usage warning for apply_to_pfn_range() and apply_to_page_range()
- Re-evaluated the decision to use apply_to_pfn_range() rather than
  modifying the pagewalk.c. It still looks like generically handling the
  transparent huge page cases requires the mmap_sem to be held at least
  in read mode, so sticking with apply_to_pfn_range() for now.
- The TTM page-fault helper vma copy argument was scratched in favour of
  a pageprot_t argument.
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Matthew Wilcox <willy at infradead.org>
Cc: Will Deacon <will.deacon at arm.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Rik van Riel <riel at surriel.com>
Cc: Minchan Kim <minchan at kernel.org>
Cc: Michal Hocko <mhocko at suse.com>
Cc: Huang Ying <ying.huang at intel.com>
Cc: Souptick Joarder <jrdr.linux at gmail.com>
Cc: "Jérôme Glisse" <jglisse at redhat.com>
Cc: "Christian König" <christian.koenig at amd.com>
Cc: linux-mm at kvack.org

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