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. -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
