linux-kernel - [PATCH v2 1/2] userfaultfd.2: Add section for UFFD_USER_MODE

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Date:   Fri,  3 Jun 2022 13:37:35 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-man@...r.kernel.org,
        linux-mm@...ck.org
Cc:     Michael Kerrisk <mtk.manpages@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alejandro Colomar <alx.manpages@...il.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, peterx@...hat.com
Subject: [PATCH v2 1/2] userfaultfd.2: Add section for UFFD_USER_MODE_ONLY

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

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

diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
index 93dca009f..6b9412aaf 100644
--- a/man2/userfaultfd.2
+++ b/man2/userfaultfd.2
@@ -12,8 +12,9 @@ Standard C library
 .RI ( libc ", " \-lc )
 .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 );
@@ -59,6 +60,15 @@ See the description of the
 .B O_NONBLOCK
 flag in
 .BR open (2).
+.TP
+.B 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
+.B 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