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 16:14:19 +0200 [thread overview]
Message-ID: <8db2474f-ecb7-0e17-5f5b-145708fe44d5@amd.com> (raw)
In-Reply-To: <20200916140710.GA8409@ziepe.ca>
Am 16.09.20 um 16:07 schrieb Jason Gunthorpe:
> On Wed, Sep 16, 2020 at 11:53:59AM +0200, Daniel Vetter wrote:
>
>> But within the driver, we generally need thousands of these, and that
>> tends to bring fd exhaustion problems with it. That's why all the private
>> buffer objects which aren't shared with other process or other drivers are
>> handles only valid for a specific fd instance of the drm chardev (each
>> open gets their own namespace), and only for ioctls done on that chardev.
>> And for mmap we assign fake (but unique across all open fd on it) offsets
>> within the overall chardev. Hence all the pgoff mangling and re-mangling.
> Are they still unique struct files? Just without a fdno?
Yes, exactly.
>> Hence why we'd like to be able to forward aliasing mappings and adjust the
>> file and pgoff, while hopefully everything keeps working. I thought this
>> would work, but Christian noticed it doesn't really.
> It seems reasonable to me that the dma buf should be the owner of the
> VMA, otherwise like you say, there is a big mess attaching the custom
> vma ops and what not to the proper dma buf.
>
> I don't see anything obviously against this in mmap_region() - why did
> Chritian notice it doesn't really work?
To clarify I think this might work.
I just had the same "Is that legal?", "What about security?", etc..
questions you raised as well.
It seems like a source of trouble so I thought better ask somebody more
familiar with that.
Christian.
>
> Jason
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WARNING: multiple messages have this Message-ID (diff)
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 16:14:19 +0200 [thread overview]
Message-ID: <8db2474f-ecb7-0e17-5f5b-145708fe44d5@amd.com> (raw)
In-Reply-To: <20200916140710.GA8409@ziepe.ca>
Am 16.09.20 um 16:07 schrieb Jason Gunthorpe:
> On Wed, Sep 16, 2020 at 11:53:59AM +0200, Daniel Vetter wrote:
>
>> But within the driver, we generally need thousands of these, and that
>> tends to bring fd exhaustion problems with it. That's why all the private
>> buffer objects which aren't shared with other process or other drivers are
>> handles only valid for a specific fd instance of the drm chardev (each
>> open gets their own namespace), and only for ioctls done on that chardev.
>> And for mmap we assign fake (but unique across all open fd on it) offsets
>> within the overall chardev. Hence all the pgoff mangling and re-mangling.
> Are they still unique struct files? Just without a fdno?
Yes, exactly.
>> Hence why we'd like to be able to forward aliasing mappings and adjust the
>> file and pgoff, while hopefully everything keeps working. I thought this
>> would work, but Christian noticed it doesn't really.
> It seems reasonable to me that the dma buf should be the owner of the
> VMA, otherwise like you say, there is a big mess attaching the custom
> vma ops and what not to the proper dma buf.
>
> I don't see anything obviously against this in mmap_region() - why did
> Chritian notice it doesn't really work?
To clarify I think this might work.
I just had the same "Is that legal?", "What about security?", etc..
questions you raised as well.
It seems like a source of trouble so I thought better ask somebody more
familiar with that.
Christian.
>
> Jason
next prev parent reply other threads:[~2020-09-16 14:14 UTC|newest]
Thread overview: 70+ 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 ` Christian König
2020-09-14 13:29 ` [PATCH 1/2] drm/shmem-helpers: revert "Redirect mmap for imported dma-buf" Christian König
2020-09-14 13:29 ` Christian König
2020-09-15 10:39 ` Daniel Vetter
2020-09-15 10:39 ` Daniel Vetter
2020-09-15 11:03 ` Christian König
2020-09-15 11:03 ` Christian König
2020-09-15 11:07 ` Daniel Vetter
2020-09-15 11:07 ` Daniel Vetter
2020-09-14 13:29 ` [PATCH 2/2] mm: introduce vma_set_file function Christian König
2020-09-14 13:29 ` Christian König
2020-09-15 9:19 ` kernel test robot
2020-09-15 9:19 ` kernel test robot
2020-09-15 9:19 ` kernel test robot
2020-09-15 11:57 ` kernel test robot
2020-09-15 11:57 ` 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 13:30 ` Christian König
2020-09-14 14:06 ` Jason Gunthorpe
2020-09-14 14:06 ` Jason Gunthorpe
2020-09-14 18:26 ` Christian König
2020-09-14 18:26 ` Christian König
2020-09-16 9:53 ` Daniel Vetter
2020-09-16 9:53 ` Daniel Vetter
2020-09-16 10:14 ` Christian König
2020-09-16 10:14 ` Christian König
2020-09-16 11:45 ` Christian König
2020-09-16 11:45 ` Christian König
2020-09-16 12:41 ` Daniel Vetter
2020-09-16 12:41 ` Daniel Vetter
2020-09-16 14:07 ` Jason Gunthorpe
2020-09-16 14:07 ` Jason Gunthorpe
2020-09-16 14:14 ` Christian König [this message]
2020-09-16 14:14 ` Christian König
2020-09-16 15:24 ` Daniel Vetter
2020-09-16 15:24 ` Daniel Vetter
2020-09-16 15:31 ` [Linaro-mm-sig] " Christian König
2020-09-16 15:31 ` Christian König
2020-09-17 6:23 ` Daniel Vetter
2020-09-17 6:23 ` Daniel Vetter
2020-09-17 7:11 ` Christian König
2020-09-17 7:11 ` Christian König
2020-09-17 8:09 ` Daniel Vetter
2020-09-17 8:09 ` Daniel Vetter
2020-09-17 11:31 ` Jason Gunthorpe
2020-09-17 11:31 ` Jason Gunthorpe
2020-09-17 12:03 ` Christian König
2020-09-17 12:03 ` Christian König
2020-09-17 12:18 ` Jason Gunthorpe
2020-09-17 12:18 ` Jason Gunthorpe
2020-09-17 12:24 ` Christian König
2020-09-17 12:24 ` Christian König
2020-09-17 12:26 ` Daniel Vetter
2020-09-17 12:26 ` Daniel Vetter
2020-09-17 14:35 ` Jason Gunthorpe
2020-09-17 14:35 ` Jason Gunthorpe
2020-09-17 14:54 ` Christian König
2020-09-17 14:54 ` Christian König
2020-09-17 15:24 ` Jason Gunthorpe
2020-09-17 15:24 ` Jason Gunthorpe
2020-09-17 15:37 ` Daniel Vetter
2020-09-17 15:37 ` Daniel Vetter
2020-09-17 16:06 ` Christian König
2020-09-17 16:06 ` Christian König
2020-09-17 16:39 ` Jason Gunthorpe
2020-09-17 16:39 ` Jason Gunthorpe
2020-09-17 17:23 ` Daniel Vetter
2020-09-17 17:23 ` Daniel Vetter
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