[PATCH 1/2] userfaultfd.2: Add section for UFFD_USER_MODE_ONLY

[Peter Xu <peterx@redhat.com>]

Add a paragraph for UFFD_USER_MODE_ONLY flag that was introduced in
Linux 5.11.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 man2/userfaultfd.2 | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
index cee7c01d2..0928a76d2 100644
--- a/man2/userfaultfd.2
+++ b/man2/userfaultfd.2
@@ -29,8 +29,9 @@
 userfaultfd \- create a file descriptor for handling page faults in user space
 .SH SYNOPSIS
 .nf
-.BR "#include <fcntl.h>" "            /* Definition of " O_* " constants */"
-.BR "#include <sys/syscall.h>" "      /* Definition of " SYS_* " constants */"
+.BR "#include <fcntl.h>" "             /* Definition of " O_* " constants */"
+.BR "#include <sys/syscall.h>" "       /* Definition of " SYS_* " constants */"
+.BR "#include <linux/userfaultfd.h>" " /* Definition of " UFFD_* " constants */"
 .B #include <unistd.h>
 .PP
 .BI "int syscall(SYS_userfaultfd, int " flags );
@@ -76,6 +77,15 @@ See the description of the
 .BR O_NONBLOCK
 flag in
 .BR open (2).
+.TP
+.BR UFFD_USER_MODE_ONLY
+This is an userfaultfd specific flag that was introduced since Linux 5.11.
+When set, the userfaultfd object will only be able to handle page faults
+originated from the userspace on the registered regions.
+When a kernel originated fault was triggered on the registered range with
+this userfaultfd, a
+.BR SIGBUS
+signal will be delivered.
 .PP
 When the last file descriptor referring to a userfaultfd object is closed,
 all memory ranges that were registered with the object are unregistered
-- 
2.32.0