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

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Message-ID: <6fd74b84-959c-8b3b-c27b-e9fbf66396c7@gmail.com>
Date:   Thu, 17 Sep 2020 14:03:48 +0200
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Jason Gunthorpe <jgg@...pe.ca>, Daniel Vetter <daniel@...ll.ch>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>, Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian König <christian.koenig@....com>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>
Subject: Re: [Linaro-mm-sig] Changing vma->vm_file in dma_buf_mmap()

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
> _______________________________________________
> Linaro-mm-sig mailing list
> Linaro-mm-sig@...ts.linaro.org
> https://lists.linaro.org/mailman/listinfo/linaro-mm-sig

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