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Subject: Re: [Linaro-mm-sig] Changing vma->vm_file in dma_buf_mmap()
To:     Jason Gunthorpe <jgg@ziepe.ca>, Daniel Vetter <daniel@ffwll.ch>
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From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <ckoenig.leichtzumerken@gmail.com>
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Date:   Thu, 17 Sep 2020 14:03:48 +0200
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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.

Christian.

>
> Jason
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