On Thu, Sep 22, 2022 at 10:39:19AM -0600, Logan Gunthorpe wrote: > GUP Callers that expect PCI P2PDMA pages can now set FOLL_PCI_P2PDMA to > allow obtaining P2PDMA pages. If GUP is called without the flag and a > P2PDMA page is found, it will return an error. > > FOLL_PCI_P2PDMA cannot be set if FOLL_LONGTERM is set. What is causing this? It is really troublesome, I would like to fix it. eg I would like to have P2PDMA pages in VFIO iommu page tables and in RDMA MR's - both require longterm. Is it just because ZONE_DEVICE was created for DAX and carried that revocable assumption over? Does anything in your series require revocable? > @@ -2383,6 +2392,10 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, > VM_BUG_ON(!pfn_valid(pte_pfn(pte))); > page = pte_page(pte); > > + if (unlikely(!(flags & FOLL_PCI_P2PDMA) && > + is_pci_p2pdma_page(page))) > + goto pte_unmap; > + > folio = try_grab_folio(page, 1, flags); > if (!folio) > goto pte_unmap; On closer look this is not in the right place, we cannot touch the content of *page without holding a ref, and that doesn't happen until until try_grab_folio() completes. It would be simpler to put this check in try_grab_folio/try_grab_page after the ref has been obtained. That will naturally cover all the places that need it. Jason
