linux-kernel - [PATCH 5/5] usefaultfd.2: add brief description of "non-cooperative" mode

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Message-Id: <1493137748-32452-6-git-send-email-rppt@linux.vnet.ibm.com>
Date:   Tue, 25 Apr 2017 19:29:08 +0300
From:   Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-man@...r.kernel.org, Mike Rapoport <rppt@...ux.vnet.ibm.com>
Subject: [PATCH 5/5] usefaultfd.2: add brief description of "non-cooperative" mode

Signed-off-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
---
 man2/userfaultfd.2 | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
index dc37319..291dd10 100644
--- a/man2/userfaultfd.2
+++ b/man2/userfaultfd.2
@@ -89,6 +89,20 @@ them using the operations described in
 .BR ioctl_userfaultfd (2).
 When servicing the page fault events,
 the fault-handling thread can trigger a wake-up for the sleeping thread.
+
+It is possible for the faulting threads and the fault-handling threads
+to run in the context of different processes.
+In this case, these threads may belong to different programs,
+and the program that executes the faulting threads
+will not necessarily cooperate with the program that handles the page faults.
+In such non-cooperative mode,
+the process that monitors userfaultfd and handles page faults,
+needs to be aware of the changes in the virtual memory layout
+of the faulting process to avoid memory corruption.
+.\" FIXME elaborate about non-cooperating mode, describe its limitations
+.\" for kerneles before 4.11, features added in 4.11
+.\" and limitations remaining in 4.11
+.\" Maybe it's worth adding a dedicated sub-section...
 .\"
 .SS Userfaultfd operation
 After the userfaultfd object is created with
-- 
1.9.1