On Wed, Aug 14, 2024 at 11:23:41AM -0400, Peter Xu wrote: > On Wed, Aug 14, 2024 at 09:40:00AM -0300, Jason Gunthorpe wrote: > > On Fri, Aug 09, 2024 at 12:08:53PM -0400, Peter Xu wrote: > > > We need these special bits to be around to enable gup-fast on pfnmaps. > > > > It is not gup-fast you are after but follow_pfn/etc for KVM usage > > right? > > Gup-fast needs it to make sure we don't pmd_page() it and fail early. So > still needed in some sort.. Yes, but making gup-fast fail is not "enabling" it :) > But yeah, this comment is ambiguous and not describing the whole picture, > as multiple places will so far rely this bit, e.g. fork() to identify a > private page or pfnmap. Similarly we'll do that in folio_walk_start(), and > follow_pfnmap. I plan to simplify that to: > > We need these special bits to be around on pfnmaps. Mark properly for > !devmap case, reflecting that there's no page struct backing the entry. Yes Jason
