Re: [PATCH 0/5] Fixup pwrite/pread with gtt mmapped user addresses

[Ben Widawsky <ben@bwidawsk.net>]

On Sat, 17 Sep 2011 20:55:44 +0200
Daniel Vetter <daniel.vetter@ffwll.ch> wrote:

> Hi all,
> 
> Original bugreport: https://bugs.freedesktop.org/show_bug.cgi?id=38115
> 
> This bug can e.g. be hit with glBufferData(dst, glBufferMap(src))
> 
> Testcase is gem_mmap_gtt.
> 
> Neglecting the trivial cleanup patch 2, patch 1 converts the possible
> deadlock in an errornous -EFAULT. I've already submitted this, but
> include it here again for completeness.  Patches 3-5 then fix this up.
> Imo there's a bit more work left to do (like properly prefaulting,
> which would have papered over this bug).  But I think this is the
> minimal set required to fix the bug and I've wanted to get early
> feedback on the approach and on possible race issues.
> 
> I think patch 3-5 are not cc:stable material because they're too
> invasive (maybe even stuff for -next). The prefaulting patch will
> be much simpler, less invasive and it essentially reduces the issue to
> a tiny race, so I suggest that for backporting.
> 
> So review, comments highly appreciated.
> 
> Yours, Daniel
> 
> Daniel Vetter (5):
>   io-mapping: ensure io_mapping_map_atomic _is_ atomic
>   drm/i915: drop KM_USER0 argument to k(un)map_atomic
>   drm/i915: fall through pwrite_gtt_slow to the shmem slow path
>   drm/i915: rewrite shmem_pwrite_slow to use copy_from_user
>   drm/i915: rewrite shmem_pread_slow to use copy_to_user
> 
>  drivers/gpu/drm/i915/i915_gem.c       |  324
> ++++++++++++++-------------------
> drivers/gpu/drm/i915/i915_gem_debug.c |    6 +-
> include/linux/io-mapping.h            |    2 + 3 files changed, 140
> insertions(+), 192 deletions(-)
> 

Still in process of review, but:
Tested-by: Ben Widawsky <ben@bwidawsk.net>