On Wed, Jan 13, 2021 at 4:43 PM Chris Wilson chris@chris-wilson.co.uk 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).
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. -Daniel