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[174.91.135.175]) by smtp.gmail.com with ESMTPSA id x1sm9627850qtr.97.2021.03.22.15.08.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Mar 2021 15:08:51 -0700 (PDT) From: Peter Xu To: linux-man@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Andrea Arcangeli , Mike Rapoport , Axel Rasmussen , Alejandro Colomar , peterx@redhat.com, Michael Kerrisk , Nadav Amit , Andrew Morton Subject: [PATCH v4 1/4] userfaultfd.2: Add UFFD_FEATURE_THREAD_ID docs Date: Mon, 22 Mar 2021 18:08:45 -0400 Message-Id: <20210322220848.52162-2-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210322220848.52162-1-peterx@redhat.com> References: <20210322220848.52162-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org UFFD_FEATURE_THREAD_ID is supported since Linux 4.14. Signed-off-by: Peter Xu --- man2/userfaultfd.2 | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 index e7dc9f813..555e37409 100644 --- a/man2/userfaultfd.2 +++ b/man2/userfaultfd.2 @@ -77,6 +77,13 @@ When the last file descriptor referring to a userfaultfd object is closed, all memory ranges that were registered with the object are unregistered and unread events are flushed. .\" +.PP +Since Linux 4.14, userfaultfd page fault message can selectively embed faulting +thread ID information into the fault message. +One needs to enable this feature explicitly using the +.BR UFFD_FEATURE_THREAD_ID +feature bit when initializing the userfaultfd context. +By default, thread ID reporting is diabled. .SS Usage The userfaultfd mechanism is designed to allow a thread in a multithreaded program to perform user-space paging for the other threads in the process. @@ -229,6 +236,9 @@ struct uffd_msg { struct { __u64 flags; /* Flags describing fault */ __u64 address; /* Faulting address */ + union { + __u32 ptid; /* Thread ID of the fault */ + } feat; } pagefault; struct { /* Since Linux 4.11 */ @@ -358,6 +368,9 @@ otherwise it is a read fault. .\" UFFD_PAGEFAULT_FLAG_WP is not yet supported. .RE .TP +.I pagefault.feat.pid +The thread ID that triggered the page fault. +.TP .I fork.ufd The file descriptor associated with the userfault object created for the child created by -- 2.26.2