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@linux-foundation.org Cc: Matthew Wilcox willy@infradead.org Cc: Will Deacon will.deacon@arm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Rik van Riel riel@surriel.com Cc: Minchan Kim minchan@kernel.org Cc: Michal Hocko mhocko@suse.com Cc: Huang Ying ying.huang@intel.com Cc: Souptick Joarder jrdr.linux@gmail.com Cc: "Jérôme Glisse" jglisse@redhat.com Cc: "Christian König" christian.koenig@amd.com Cc: linux-mm@kvack.org