[PATCH v2 4/6] UFFDIO_API.2const: Document UFFD_FEATURE_RWP{,_ASYNC} and 1 << _UFFDIO_SET_MODE

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.

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 <[email protected]>
Acked-by: Mike Rapoport (Microsoft) <[email protected]>
---
 man/man2const/UFFDIO_API.2const | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/man/man2const/UFFDIO_API.2const b/man/man2const/UFFDIO_API.2const
index e894114bb8e2..46ee7e31fed9 100644
--- a/man/man2const/UFFDIO_API.2const
+++ b/man/man2const/UFFDIO_API.2const
@@ -213,6 +213,30 @@ .SH DESCRIPTION
 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 +258,13 @@ .SH DESCRIPTION
 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