[PATCH v2] drm/gem: Fix mmap fake offset handling for drm_gem_object_funcs.mmap

[Daniel Vetter]

On Fri, Nov 15, 2019 at 10:37 AM Gerd Hoffmann <kraxel at redhat.com> wrote:
>
> > You need memory pressure, to force ttm to unmap the bo, not userspace. So
> > roughly
> > 1. create bo
> > 2. mmap it through drm fd, write some stuff
> > 3. export to dma-buf, mmap it, verify stuff is there
> > 4. create a pile more bo, mmap them write to them
> > 5. once you've thrashed all of vram enough, recheck your original bo. If
> > I'm right you should get the following:
> >    - drm fd mmap still show right content
> >    - dma-buf fd mmap shows random crap that you've written into other
> >      buffers
> >
> > Ofc you need to make sure that an mmap actually forces the buffer into
> > vram. So might need a combo of modeset+mmap, to make that happen. Plain
> > mmap might just give you ptes that point into system memory, which is not
> > managed by ttm like vram.
>
> Is any move buffer good enough to trigger this, i.e. will SYSTEM -> VRAM
> work too?  That'll be easier because all I need to do is map the buffer
> to a crtc to force pinning to vram, then check if the mappings are
> intact still ...

I think that should work too. Just make sure you actually write
through SYSTEM first (maybe with some printk or whatever).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch