Re: [PATCH v2 04/14] mm: add VM_UFFD_RWP VMA flag

[Mike Rapoport <rppt@kernel.org>]

On Fri, May 08, 2026 at 04:55:16PM +0100, Kiryl Shutsemau (Meta) wrote:
> Preparatory patch for userfaultfd read-write protection (RWP). RWP
> extends userfaultfd protection from plain write-protection (WP) to
> full read-write protection: accesses to an RWP-protected range --
> reads as well as writes -- trap through userfaultfd.
> 
> RWP marks ranges by combining PAGE_NONE with the uffd PTE bit, so
> the flag is only meaningful when both primitives exist. A new
> CONFIG_USERFAULTFD_RWP Kconfig symbol auto-selects when CONFIG_64BIT,
> CONFIG_ARCH_HAS_PTE_PROTNONE, and CONFIG_HAVE_ARCH_USERFAULTFD_WP
> are all set; call sites that gate on the flag depend on the symbol.
> Elsewhere VM_UFFD_RWP aliases VM_NONE and every downstream check
> folds to dead code.
> 
> Nothing sets the flag yet.

And nothing check for it as well, am I right?
Worth noting here, IMHO.
 
> Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
> Assisted-by: Claude:claude-opus-4-6
> ---
>  Documentation/filesystems/proc.rst |  1 +
>  fs/proc/task_mmu.c                 |  3 +++
>  include/linux/mm.h                 | 28 +++++++++++++++++----------
>  include/linux/userfaultfd_k.h      | 31 +++++++++++++++++++++++++-----
>  include/trace/events/mmflags.h     |  7 +++++++
>  mm/Kconfig                         |  9 +++++++++
>  6 files changed, 64 insertions(+), 15 deletions(-)
> 
> diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
> index 98f546e83cd2..fcf308dba311 100644
> --- a/include/linux/userfaultfd_k.h
> +++ b/include/linux/userfaultfd_k.h
> @@ -21,10 +21,11 @@
>  #include <linux/hugetlb_inline.h>
>  
>  /* The set of all possible UFFD-related VM flags. */
> -#define __VM_UFFD_FLAGS (VM_UFFD_MISSING | VM_UFFD_WP | VM_UFFD_MINOR)
> +#define __VM_UFFD_FLAGS (VM_UFFD_MISSING | VM_UFFD_WP | VM_UFFD_MINOR | \
> +			 VM_UFFD_RWP)

Nit: can we keep mode bits together and protection bits together here and
in the below changes?

Otherwise looks good to me

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

>  #define __VMA_UFFD_FLAGS mk_vma_flags(VMA_UFFD_MISSING_BIT, VMA_UFFD_WP_BIT, \
> -				      VMA_UFFD_MINOR_BIT)
> +				      VMA_UFFD_MINOR_BIT, VMA_UFFD_RWP_BIT)
>  
>  /*
>   * CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining
> @@ -192,7 +193,7 @@ static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma,
>   */
>  static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma)
>  {
> -	return vma->vm_flags & (VM_UFFD_WP | VM_UFFD_MINOR);
> +	return vma->vm_flags & (VM_UFFD_WP | VM_UFFD_MINOR | VM_UFFD_RWP);
>  }
>  
>  /*
> @@ -222,6 +223,16 @@ static inline bool userfaultfd_minor(struct vm_area_struct *vma)
>  	return vma->vm_flags & VM_UFFD_MINOR;
>  }
>  
> +static inline bool userfaultfd_rwp(struct vm_area_struct *vma)
> +{
> +	return vma->vm_flags & VM_UFFD_RWP;
> +}
> +
> +static inline bool userfaultfd_protected(struct vm_area_struct *vma)
> +{
> +	return userfaultfd_wp(vma) || userfaultfd_rwp(vma);
> +}
> +
>  static inline bool userfaultfd_pte_wp(struct vm_area_struct *vma,
>  				      pte_t pte)
>  {

-- 
Sincerely yours,
Mike.