On Thu, Jan 14, 2021 at 1:03 AM Daniel Vetter <daniel.vetter@xxxxxxxx> wrote: > > On Wed, Jan 13, 2021 at 10:08 PM Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote: > > Quoting Daniel Vetter (2021-01-13 20:50:11) > > > On Wed, Jan 13, 2021 at 4:43 PM Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > Quoting Daniel Vetter (2021-01-13 14:06:04) > > > > > We have too many people abusing the struct page they can get at but > > > > > really shouldn't in importers. Aside from that the backing page might > > > > > simply not exist (for dynamic p2p mappings) looking at it and using it > > > > > e.g. for mmap can also wreak the page handling of the exporter > > > > > completely. Importers really must go through the proper interface like > > > > > dma_buf_mmap for everything. > > > > > > > > If the exporter doesn't want to expose the struct page, why are they > > > > setting it in the exported sg_table? > > > > > > You need to store it somewhere, otherwise the dma-api doesn't work. > > > Essentially this achieves clearing/resetting the struct page pointer, > > > without additional allocations somewhere, or tons of driver changes > > > (since presumably the driver does keep track of the struct page > > > somewhere too). > > > > Only for mapping, and that's before the export -- if there's even a > > struct page to begin with. > > > > > Also as long as we have random importers looking at struct page we > > > can't just remove it, or crashes everywhere. So it has to be some > > > debug option you can disable. > > > > Totally agreed that nothing generic can rely on pages being transported > > via dma-buf, and memfd is there if you do want a suitable transport. The > > one I don't know about is dma-buf heap, do both parties there consent to > > transport pages via the dma-buf? i.e. do they have special cases for > > import/export between heaps? > > heaps shouldn't be any different wrt the interface exposed to > importers. Adding John just in case I missed something. I'm not aware of how this would be an issue right off for dma-buf heaps. Obviously there may be some corner cases with things like secure heaps, but I've not gotten to work on any of those yet and there's none in-tree. I did test out the patch on HiKey960 (using the cma and system heap for display and gpu buffers - admittedly not particularly complex) and didn't see any issues with it enabled. I've added Suren and Hridya for more input but don't have any objections right off. thanks -john
