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[174.91.135.175]) by smtp.gmail.com with ESMTPSA id i17sm12255215qtr.33.2021.03.29.15.18.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 29 Mar 2021 15:18:36 -0700 (PDT) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-man@vger.kernel.org Cc: Axel Rasmussen , peterx@redhat.com, Nadav Amit , Mike Rapoport , Alejandro Colomar , Andrea Arcangeli , Michael Kerrisk , Andrew Morton Subject: [PATCH v5 1/4] userfaultfd.2: Add UFFD_FEATURE_THREAD_ID docs Date: Mon, 29 Mar 2021 18:18:30 -0400 Message-Id: <20210329221833.517923-2-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210329221833.517923-1-peterx@redhat.com> References: <20210329221833.517923-1-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-Rspamd-Queue-Id: 441CB500152D X-Stat-Signature: jek5gzyhguhbux7oq4k1abs46fxaqqc3 X-Rspamd-Server: rspam02 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf01; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=63.128.21.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617056320-592701 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. Acked-by: Mike Rapoport 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..5c41e4816 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 disabled. .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