On Thu, Sep 17, 2020 at 02:24:29PM +0200, Christian König wrote: > Am 17.09.20 um 14:18 schrieb Jason Gunthorpe: > > On Thu, Sep 17, 2020 at 02:03:48PM +0200, Christian König wrote: > > > Am 17.09.20 um 13:31 schrieb Jason Gunthorpe: > > > > On Thu, Sep 17, 2020 at 10:09:12AM +0200, Daniel Vetter wrote: > > > > > > > > > Yeah, but it doesn't work when forwarding from the drm chardev to the > > > > > dma-buf on the importer side, since you'd need a ton of different > > > > > address spaces. And you still rely on the core code picking up your > > > > > pgoff mangling, which feels about as risky to me as the vma file > > > > > pointer wrangling - if it's not consistently applied the reverse map > > > > > is toast and unmap_mapping_range doesn't work correctly for our needs. > > > > I would think the pgoff has to be translated at the same time the > > > > vm->vm_file is changed? > > > > > > > > The owner of the dma_buf should have one virtual address space and FD, > > > > all its dma bufs should be linked to it, and all pgoffs translated to > > > > that space. > > > Yeah, that is exactly like amdgpu is doing it. > > > > > > Going to document that somehow when I'm done with TTM cleanups. > > BTW, while people are looking at this, is there a way to go from a VMA > > to a dma_buf that owns it? > > Only a driver specific one. Sounds OK > For TTM drivers vma->vm_private_data points to the buffer object. Not sure > about the drivers using GEM only. Why are drivers in control of the vma? I would think dma_buf should be the vma owner. IIRC module lifetime correctness essentially hings on the module owner of the struct file > Why are you asking? I'm thinking about using find_vma on something that is not get_user_pages()'able to go to the underlying object, in this case dma buf. So, user VA -> find_vma -> dma_buf object -> dma_buf operations on the memory it represents Jason
