On Wed, Sep 16, 2020 at 5:31 PM Christian König <ckoenig.leichtzumerken@xxxxxxxxx> wrote: > > Am 16.09.20 um 17:24 schrieb Daniel Vetter: > > On Wed, Sep 16, 2020 at 4:14 PM Christian König > > <christian.koenig@xxxxxxx> 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. Yes dma-buf, but that gets forwarded to the original drm chardev which originally exported the buffer. It's only there where the forwarding chain stops. The other thing is that iirc we have a singleton anon_inode behind all the dma-buf, so they'd share all the same address_space and so would all alias for unmap_mapping_range (I think at least). -Daniel > > 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@xxxxxxxxxxxxxxxxxxxxx > >> https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
