On Fri, Jul 12, 2024 at 09:42:37AM -0300, Jason Gunthorpe wrote: > On Fri, Jul 12, 2024 at 06:54:22AM +0200, Christoph Hellwig wrote: > > > This is all purely hypothetical, and I'm happy to just check for it > > and reject it for it now. > > I do know a patch set is cooking to allow mixing ZONE_DEVICE P2P and > anon memory in the same VMA ala HMM with transparent migration of > ZONE_DEVICE to anon. > > In this situation userspace will be generating IO with no idea about > any P2P/!P2P boundaries. Yes. And as said from the beginning of these discussion I think the right way is to change the gup code so that for a single call to get/pin_user_pages it always returns either only P2P pages or non-P2P pages only, with the FOLL_PCI_P2PDMA just allowing P2P pages at all. Similarly they could easily just return one kind of P2P pages per call only.
