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

[Kiryl Shutsemau <kas@kernel.org>]

On Tue, May 12, 2026 at 07:48:57PM +0300, Mike Rapoport wrote:
> 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?

Yep.

> Worth noting here, IMHO.

Will do.

>  
> > 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?

Yep, make sense.

> Otherwise looks good to me
> 
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Thanks!

-- 
  Kiryl Shutsemau / Kirill A. Shutemov