On Thu, Dec 03, 2020 at 11:10:18PM -0500, Andrea Arcangeli wrote: > from the pte, one that cannot ever be set in any swp entry today. I > assume it can't be _PAGE_SWP_UFFD_WP since that already can be set but > you may want to verify it... I thought more about the above, and I think the already existing pte_swp_mkuffd_wp will just be enough without having to reserve an extra bitflag if we encode it as a non migration entry. The check: if (!pte_present && !pte_none && pte_swp_uffd_wp && not_anonymous_vma && !is_migration_entry) should be enough to disambiguate it. When setting it, it'd be enough to set the pte to the value _PAGE_SWP_UFFD_WP. Although if you prefer to check for: if (!pte_present && !pte_none && swp_type == 1 && swp_offset == 0 && not_anonymous_vma && !is_migration_entry) that would do as well. It's up to you, just my preference is to reuse _PAGE_SWP_UFFD_WP since it has already to exist, there are already all the pte_swp_*uffd* methods available or uffd-wp cannot work. Thanks, Andrea
