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[174.95.95.253]) by smtp.gmail.com with ESMTPSA id b7sm18610766qkj.115.2021.03.03.17.59.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Mar 2021 17:59:50 -0800 (PST) From: Peter Xu To: linux-man@vger.kernel.org Cc: Mike Rapoport , Nadav Amit , linux-kernel@vger.kernel.org, Linux MM Mailing List , peterx@redhat.com, Axel Rasmussen , Alejandro Colomar , Andrea Arcangeli , Andrew Morton , Michael Kerrisk Subject: [PATCH 1/4] userfaultfd.2: Add UFFD_FEATURE_THREAD_ID docs Date: Wed, 3 Mar 2021 20:59:44 -0500 Message-Id: <20210304015947.517713-2-peterx@redhat.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210304015947.517713-1-peterx@redhat.com> References: <20210304015947.517713-1-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: 1jp6k7mwks51isryj5gofi6kqupifb4s X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 60A26E0011E1 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf30; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=216.205.24.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614823193-334386 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 | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 index e7dc9f813..2d14effc6 100644 --- a/man2/userfaultfd.2 +++ b/man2/userfaultfd.2 @@ -77,6 +77,12 @@ 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= ault +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, otherwise disable= d. .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 +235,9 @@ 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 +367,9 @@ 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