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

Jason Gunthorpe
2020-09-17T11:39:19Z

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.

Jason