On Thu, Jan 19, 2023 at 12:15:44AM +0000, Al Viro wrote: > Actually, looking at that thing... Currently we use it only for > FOLL_PCI_P2PDMA. It alters behaviour of get_user_pages_fast(), but... > it is completely ignored for ITER_BVEC or ITER_PIPE. So how the > hell is it supposed to work? It broadens the acceptance criteria for UBUF/IOVEC types. It doesn't change behavior for already accepted memory for those or any others. > Could somebody give a braindump on that thing? It looks like we > have pages that should not be DMA'd to/from unless driver takes > some precautions and we want to make sure they won't be fed to > drivers that don't take such. With checks done in a very odd > place... Yes, normal gup excludes P2P pages. This flag allows it to get them.
