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

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 ...

cheers, Gerd