Quoting Daniel Vetter (2021-01-14 09:47:40) > On Thu, Jan 14, 2021 at 09:45:37AM +0000, Chris Wilson wrote: > > Quoting Daniel Vetter (2021-01-14 09:30:32) > > > On Thu, Jan 14, 2021 at 10:23 AM Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote: > > > > The only other problem I see with the implementation is that there's > > > > nothing that says that each dmabuf->ops->map_dma_buf() returns a new > > > > sg_table, so we may end up undoing the xor. Or should each dma-buf > > > > return a fresh dma-mapping for iommu isolation? > > > > > > Maybe I screwed it up, but that's why I extracted the little helpers: > > > We scramble when we get the sgtable from exporter, and unscramble > > > before we pass it back. dma-buf.c does some caching and will hand back > > > the same sgtable, but for that case we don't re-scramble. > > > > The attachment is only mapped once, but there can be more than one > > attachment, and the backend could return the same sg_table for each > > mapping. Conceivably, it could return its own private sg_table where it > > wants to maintain the struct page. Seems like just adding a sentence to > > @map_dma_buf to clarify that each call should return a new sg_table will > > suffice. > > Ah yes good point, will augment (once CI stops being angry at me). Fwiw, with a quick explanation of "don't do this" in the docs, Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> -Chris
