Re: [PATCH v3 05/16] mm: add MM_CP_UFFD_RWP change_protection() flag

On Fri, May 22, 2026 at 02:38:46PM +0100, Kiryl Shutsemau wrote:
> From: "Kiryl Shutsemau (Meta)" <[email protected]>
> 
> Preparatory patch. Add the change_protection() primitive that
> userfaultfd RWP will use.
> 
> An RWP-protected PTE is PAGE_NONE with the uffd PTE bit set. The
> PROT_NONE half makes the CPU fault on any access; the uffd bit
> distinguishes an RWP fault from a plain mprotect(PROT_NONE) or NUMA
> hinting fault. MM_CP_UFFD_WP and MM_CP_UFFD_RWP share the same PTE
> bit, so the two cannot be used together on the same range.
> 
> Two new change_protection() flags:
> 
>   MM_CP_UFFD_RWP            install PAGE_NONE and set the uffd bit
>   MM_CP_UFFD_RWP_RESOLVE    restore vma->vm_page_prot, clear the uffd bit
> 
> Both are wired through change_pte_range(), change_huge_pmd(), and
> hugetlb_change_protection() so anon, shmem, THP, and hugetlb all
> share the same semantics.
> 
> Signed-off-by: Kiryl Shutsemau <[email protected]>
> Assisted-by: Claude:claude-opus-4-6

Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>

> ---
>  include/linux/mm.h            |  5 ++++
>  include/linux/userfaultfd_k.h |  1 -
>  mm/huge_memory.c              | 30 +++++++++++++----------
>  mm/hugetlb.c                  | 25 ++++++++++++++-----
>  mm/mprotect.c                 | 46 +++++++++++++++++++++++++++--------
>  5 files changed, 77 insertions(+), 30 deletions(-)

-- 
Sincerely yours,
Mike.