Re: [Linaro-mm-sig] Changing vma->vm_file in dma_buf_mmap()

From: Christian König
Date: Thu Sep 17 2020 - 08:12:13 EST

Am 17.09.20 um 13:31 schrieb Jason Gunthorpe:
On Thu, Sep 17, 2020 at 10:09:12AM +0200, Daniel Vetter wrote:

Yeah, but it doesn't work when forwarding from the drm chardev to the
dma-buf on the importer side, since you'd need a ton of different
address spaces. And you still rely on the core code picking up your
pgoff mangling, which feels about as risky to me as the vma file
pointer wrangling - if it's not consistently applied the reverse map
is toast and unmap_mapping_range doesn't work correctly for our needs.
I would think the pgoff has to be translated at the same time the
vm->vm_file is changed?

The owner of the dma_buf should have one virtual address space and FD,
all its dma bufs should be linked to it, and all pgoffs translated to
that space.

Yeah, that is exactly like amdgpu is doing it.

Going to document that somehow when I'm done with TTM cleanups.


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