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Wed, 10 Mar 2021 14:23:02 -0800 (PST) From: Peter Xu To: linux-man@vger.kernel.org Cc: Andrea Arcangeli , Michael Kerrisk , Axel Rasmussen , linux-kernel@vger.kernel.org, peterx@redhat.com, Linux MM Mailing List , Andrew Morton , Alejandro Colomar , Nadav Amit , Mike Rapoport Subject: [PATCH v3 1/4] userfaultfd.2: Add UFFD_FEATURE_THREAD_ID docs Date: Wed, 10 Mar 2021 17:22:57 -0500 Message-Id: <20210310222300.200054-2-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210310222300.200054-1-peterx@redhat.com> References: <20210310222300.200054-1-peterx@redhat.com> MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="US-ASCII" X-Stat-Signature: z94o9ezxuf167geyczak8c1hypwimtor X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: CD8302000391 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf28; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=170.10.133.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615414989-991728 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 userfault= fd 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 f= aulting +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 multithread= ed program to perform user-space paging for the other threads in the proces= s. @@ -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; =20 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 --=20 2.26.2