Messages in this thread | | | Subject | Re: [Linaro-mm-sig] Changing vma->vm_file in dma_buf_mmap() | From | Christian König <> | Date | Wed, 16 Sep 2020 17:31:31 +0200 |
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Am 16.09.20 um 17:24 schrieb Daniel Vetter: > On Wed, Sep 16, 2020 at 4:14 PM Christian König > <christian.koenig@amd.com> wrote: >> 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. > Not entirely, since dma-buf happened after drm chardev, so for that > historical reason the underlying struct file is shared, since it's the > drm chardev. But since that's per-device we don't have a problem in > practice with different vm_ops, since those are also per-device. But > yeah we could fish out some entirely hidden per-object struct file if > that's required for some mm internal reasons.
Hui? Ok that is just the handling in i915, isn't it?
As far as I know we create an unique struct file for each DMA-buf.
Regards, Christian.
> -Daniel > >>>> 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 >> _______________________________________________ >> dri-devel mailing list >> dri-devel@lists.freedesktop.org >> https://lists.freedesktop.org/mailman/listinfo/dri-devel > >
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