Re: [PATCH man-pages v1 4/6] UFFDIO_API.2const: Document UFFD_FEATURE_RWP{,_ASYNC} and 1 << _UFFDIO_SET_MODE

[Alejandro Colomar <alx@kernel.org>]

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On 2026-05-25T16:00:37+0200, Alejandro Colomar wrote:
> Hi Kiryl,
> 
> On 2026-05-25T13:28:14+0100, Kiryl Shutsemau wrote:
> > Add the two RWP feature bits introduced in Linux 7.2:
> > 
> >   UFFD_FEATURE_RWP        gates UFFDIO_REGISTER_MODE_RWP and the
> >                           UFFDIO_RWPROTECT(2const) ioctl.
> >   UFFD_FEATURE_RWP_ASYNC  in-kernel resolution of RWP faults without
> >                           delivering a notification; requires
> >                           UFFD_FEATURE_RWP to be set in the same
> >                           UFFDIO_API call.
> > 
> > Also document 1 << _UFFDIO_SET_MODE in argp->ioctls, the
> > file-descriptor-level bit that advertises UFFDIO_SET_MODE(2const) for
> > toggling UFFD_FEATURE_RWP_ASYNC at runtime; it is independent of any
> > registered range.
> 
> Would you mind separating these into 3 patches?  Thanks!

Actually, I retire this.  I think it makes sense as a single patch.

Cheers,
Alex

> 
> > 
> > The existing page intro already describes UFFDIO_API returning EINVAL
> > on unsupported feature bits and the temporary-uffd probe pattern, so
> > the new TP entries do not re-state that.
> > 
> > Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
> 
> 
> Have a lovely day!
> Alex
> 
> > ---
> >  man/man2const/UFFDIO_API.2const | 29 +++++++++++++++++++++++++++++
> >  1 file changed, 29 insertions(+)
> > 
> > diff --git a/man/man2const/UFFDIO_API.2const b/man/man2const/UFFDIO_API.2const
> > index e894114bb8e2..d2819f009f97 100644
> > --- a/man/man2const/UFFDIO_API.2const
> > +++ b/man/man2const/UFFDIO_API.2const
> > @@ -213,6 +213,28 @@ If this feature bit is set,
> >  the kernel supports resolving faults with the
> >  .B UFFDIO_MOVE
> >  ioctl.
> > +.TP
> > +.BR UFFD_FEATURE_RWP " (since Linux 7.2)"
> > +If this feature bit is set,
> > +the kernel supports read-write protection tracking, and the
> > +.B UFFDIO_REGISTER_MODE_RWP
> > +registration mode and the
> > +.B UFFDIO_RWPROTECT
> > +ioctl become available.
> > +.TP
> > +.BR UFFD_FEATURE_RWP_ASYNC " (since Linux 7.2)"
> > +If this feature bit is set,
> > +the kernel will resolve read-write protect faults in place without
> > +delivering a notification, automatically restoring page permissions and
> > +letting the faulted thread continue.
> > +This bit requires
> > +.B UFFD_FEATURE_RWP
> > +to be set in the same
> > +.B UFFDIO_API
> > +call.
> > +The async mode can also be toggled at runtime using the
> > +.BR UFFDIO_SET_MODE (2const)
> > +ioctl.
> >  .P
> >  The returned
> >  .I argp->ioctls
> > @@ -234,6 +256,13 @@ operation is supported.
> >  The
> >  .B UFFDIO_UNREGISTER
> >  operation is supported.
> > +.TP
> > +.BR "1 << _UFFDIO_SET_MODE" " (since Linux 7.2)"
> > +The
> > +.B UFFDIO_SET_MODE
> > +operation is supported.
> > +This is a file-descriptor-level ioctl and is reported once per
> > +userfaultfd, independent of any registered range.
> >  .SH RETURN VALUE
> >  On success,
> >  0 is returned.
> > -- 
> > 2.54.0
> > 
> > 
> 
> -- 
> <https://www.alejandro-colomar.es>



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