linux-kernel - [PATCH 2/2] userfaultfd.2: Update on write-protection support

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Message-Id: <20220531011157.46868-3-peterx@redhat.com>
Date:   Mon, 30 May 2022 21:11:57 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-man@...r.kernel.org,
        linux-mm@...ck.org
Cc:     Alejandro Colomar <alx.manpages@...il.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>, peterx@...hat.com,
        Nadav Amit <nadav.amit@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 2/2] userfaultfd.2: Update on write-protection support

The shmem/hugetlbfs memory types are supported for write-protection
messages very lately.  Update the man page to reflect that.

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 man2/userfaultfd.2 | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
index 0928a76d2..99aae8b50 100644
--- a/man2/userfaultfd.2
+++ b/man2/userfaultfd.2
@@ -273,13 +273,17 @@ Since Linux 4.11,
 userfaultfd can be also used with hugetlbfs and shared memory mappings.
 .\"
 .SS Userfaultfd write-protect mode (since 5.7)
-Since Linux 5.7, userfaultfd supports write-protect mode.
+Since Linux 5.7, userfaultfd supports write-protect mode for anonymous memory.
 The user needs to first check availability of this feature using
 .B UFFDIO_API
 ioctl against the feature bit
 .B UFFD_FEATURE_PAGEFAULT_FLAG_WP
 before using this feature.
 .PP
+Since Linux 5.19, the write-protection mode was also supported on shmem and hugetlbfs
+memory types. It can be detected with the feature bit
+.BR UFFD_FEATURE_WP_HUGETLBFS_SHMEM .
+.PP
 To register with userfaultfd write-protect mode, the user needs to initiate the
 .B UFFDIO_REGISTER
 ioctl with mode
@@ -330,8 +334,6 @@ ioctl, whose
 should have the flag
 .B UFFDIO_WRITEPROTECT_MODE_WP
 cleared upon the faulted page or range.
-.PP
-Write-protect mode supports only private anonymous memory.
 .SS Reading from the userfaultfd structure
 Each
 .BR read (2)
-- 
2.32.0