On Thu, Jun 24, 2021 at 10:07:14AM +0200, Christian König wrote: > The key point is that accessing the underlying pages even when DMA-bufs are > backed by system memory is illegal. Daniel even created a patch which > mangles the page pointers in sg_tables used by DMA-buf to make sure that > people don't try to use them. Which is another goddamn layering violation of a subsystem that has no business at all poking into the scatterlist structure, yes. > So the conclusion is that using sg_table in the DMA-buf framework was just > the wrong data structure and we should have invented a new one. I think so. > But then people would have complained that we have a duplicated > infrastructure (which is essentially true). I doubt it. At least if you had actually talked to the relevant people. Which seems to be a major issue with what is going on GPU land. > My best plan to get out of this mess is that we change the DMA-buf > interface to use an array of dma_addresses instead of the sg_table object > and I have already been working on this actively the last few month. Awesome! I have a bit of related work on the DMA mapping subsystems, so let's sync up as soon as you have some first sketches. Btw, one thing I noticed when looking over the dma-buf instances is that there is a lot of duplicated code for creating a sg_table from pages, and then mapping it. It would be good if we could move toward common helpers instead of duplicating that all over again.
