From: "Christian König" <christian.koenig@amd.com>
To: Jason Gunthorpe <jgg@ziepe.ca>,
akpm@linux-foundation.org, sumit.semwal@linaro.org,
linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: Changing vma->vm_file in dma_buf_mmap()
Date: Wed, 16 Sep 2020 13:45:43 +0200 [thread overview]
Message-ID: <b621db68-30b9-cc3f-c2c0-237a7fe4db09@amd.com> (raw)
In-Reply-To: <fc8f2af7-9fc2-cb55-3065-75a4060b7c82@amd.com>
[-- Attachment #1: Type: text/plain, Size: 1444 bytes --]
[SNIP]
> But Jason pointed me to the right piece of code. See this comment in
> in mmap_region():
>
>> /* ->mmap() can change vma->vm_file, but must guarantee that
>> * vma_link() below can deny write-access if VM_DENYWRITE is set
>> * and map writably if VM_SHARED is set. This usually means the
>> * new file must not have been exposed to user-space, yet.
>> */
>> vma <https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/vma>->vm_file
>> <https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/vm_file> = get_file
>> <https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/get_file>(file
>> <https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/file>);
>> error = call_mmap
>> <https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/call_mmap>(file
>> <https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/file>, vma <https://elixir.bootlin.com/linux/v5.9-rc5/C/ident/vma>);
>
> So changing vma->vm_file is allowed at least under certain circumstances.
>
> Only the "file must not have been exposed to user-space, yet" part
> still needs double checking. Currently working on that.
Ok, I think we can guarantee for all DMA-bufs what is required here.
While searching the code I've found that at least vgem_prime_mmap() and
i915_gem_dmabuf_mmap() are doing the same thing of modifying vma->vm_file.
So I'm leaning towards that this works as expected and we should just
document this properly.
Daniel and Jason what do you think?
Christian.
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next prev parent reply other threads:[~2020-09-16 11:45 UTC|newest]
Thread overview: 34+ 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
2020-09-16 10:14 ` Christian König
2020-09-16 11:45 ` Christian König [this message]
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
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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