From: Jason Gunthorpe <jgg@ziepe.ca>
To: christian.koenig@amd.com
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
dri-devel <dri-devel@lists.freedesktop.org>,
"moderated list:DMA BUFFER SHARING FRAMEWORK"
<linaro-mm-sig@lists.linaro.org>, Linux MM <linux-mm@kvack.org>,
Daniel Vetter <daniel@ffwll.ch>,
Andrew Morton <akpm@linux-foundation.org>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@vger.kernel.org>
Subject: Re: [Linaro-mm-sig] Changing vma->vm_file in dma_buf_mmap()
Date: Thu, 17 Sep 2020 11:35:51 -0300 [thread overview]
Message-ID: <20200917143551.GG8409@ziepe.ca> (raw)
In-Reply-To: <d82f08ee-2dec-18e8-fb06-d26f18ed777a@gmail.com>
On Thu, Sep 17, 2020 at 02:24:29PM +0200, Christian König wrote:
> Am 17.09.20 um 14:18 schrieb Jason Gunthorpe:
> > On Thu, Sep 17, 2020 at 02:03:48PM +0200, Christian König wrote:
> > > 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.
> > BTW, while people are looking at this, is there a way to go from a VMA
> > to a dma_buf that owns it?
>
> Only a driver specific one.
Sounds OK
> For TTM drivers vma->vm_private_data points to the buffer object. Not sure
> about the drivers using GEM only.
Why are drivers in control of the vma? I would think dma_buf should be
the vma owner. IIRC module lifetime correctness essentially hings on
the module owner of the struct file
> Why are you asking?
I'm thinking about using find_vma on something that is not
get_user_pages()'able to go to the underlying object, in this case dma
buf.
So, user VA -> find_vma -> dma_buf object -> dma_buf operations on the
memory it represents
Jason
next prev parent reply other threads:[~2020-09-17 14:39 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-14 13:29 Changing vma->vm_file in dma_buf_mmap() Christian König
2020-09-14 13:29 ` [PATCH 1/2] drm/shmem-helpers: revert "Redirect mmap for imported dma-buf" Christian König
2020-09-15 10:39 ` Daniel Vetter
2020-09-15 11:03 ` Christian König
2020-09-15 11:07 ` Daniel Vetter
2020-09-14 13:29 ` [PATCH 2/2] mm: introduce vma_set_file function Christian König
2020-09-15 9:19 ` kernel test robot
2020-09-15 11:57 ` kernel test robot
2020-09-14 13:30 ` Changing vma->vm_file in dma_buf_mmap() Christian König
2020-09-14 14:06 ` Jason Gunthorpe
2020-09-14 18:26 ` Christian König
2020-09-16 9:53 ` Daniel Vetter
[not found] ` <fc8f2af7-9fc2-cb55-3065-75a4060b7c82@amd.com>
[not found] ` <b621db68-30b9-cc3f-c2c0-237a7fe4db09@amd.com>
2020-09-16 12:41 ` Daniel Vetter
2020-09-16 14:07 ` Jason Gunthorpe
2020-09-16 14:14 ` Christian König
2020-09-16 15:24 ` Daniel Vetter
2020-09-16 15:31 ` [Linaro-mm-sig] " Christian König
2020-09-17 6:23 ` Daniel Vetter
2020-09-17 7:11 ` Christian König
2020-09-17 8:09 ` Daniel Vetter
2020-09-17 11:31 ` Jason Gunthorpe
2020-09-17 12:03 ` Christian König
2020-09-17 12:18 ` Jason Gunthorpe
2020-09-17 12:24 ` Christian König
2020-09-17 12:26 ` Daniel Vetter
2020-09-17 14:35 ` Jason Gunthorpe [this message]
2020-09-17 14:54 ` Christian König
2020-09-17 15:24 ` Jason Gunthorpe
2020-09-17 15:37 ` Daniel Vetter
2020-09-17 16:06 ` Christian König
2020-09-17 16:39 ` Jason Gunthorpe
2020-09-17 17:23 ` Daniel Vetter
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