From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 27AC9C433DB for ; Wed, 10 Mar 2021 22:23:10 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C189164FB9 for ; Wed, 10 Mar 2021 22:23:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C189164FB9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A70988D023C; Wed, 10 Mar 2021 17:23:08 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A44868D0243; Wed, 10 Mar 2021 17:23:08 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 822478D023C; Wed, 10 Mar 2021 17:23:08 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0243.hostedemail.com [216.40.44.243]) by kanga.kvack.org (Postfix) with ESMTP id 67A7B8D0243 for ; Wed, 10 Mar 2021 17:23:08 -0500 (EST) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 30B61180ACC31 for ; Wed, 10 Mar 2021 22:23:08 +0000 (UTC) X-FDA: 77905391256.13.60DFF95 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf21.hostedemail.com (Postfix) with ESMTP id 8DDB7E000106 for ; Wed, 10 Mar 2021 22:23:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615414986; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+HBMhwNDuSkuTKHptQidlV5B3gcNKniJIMjHDTB7rlE=; b=dRXKqA8J3tFZuwwnv4RIWmn9ziaQOR9/fpAQhJrs+lY3AT/JhjgKmPd3If0MZ69xfUoMLk 5UXb718x/kSIkR3ZE3rU4wRHmO+HO4/Pj0+Cg7nvZX/IR+Aezf6xJTuKiKO1SWKgjqIKxW VsxdiV9BS1P91i03LgfLdVMSRQF8EqM= Received: from mail-qt1-f199.google.com (mail-qt1-f199.google.com [209.85.160.199]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-569-dIVJe_8PMsmdGJvJ0Uv7Aw-1; Wed, 10 Mar 2021 17:23:05 -0500 X-MC-Unique: dIVJe_8PMsmdGJvJ0Uv7Aw-1 Received: by mail-qt1-f199.google.com with SMTP id t19so14058529qta.2 for ; Wed, 10 Mar 2021 14:23:05 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=+HBMhwNDuSkuTKHptQidlV5B3gcNKniJIMjHDTB7rlE=; b=UbVJG5Oh1HRiEatUSp06X+C6RvHs6zKTvs9hlM01mho7wOqpcOl/JfgptqeIHyhYPL b66Yj/x5BdjqM1LiM0ZOCngtuddZWpcZDKHYWqFglOfNY6siXW3+Arq1AENG0Vr6asiG rRtkp0c4i27Hg0MnEp55iGZn+pciJRgSHLEQe9nTTHOBbM6xJFUq3I2BGXpPH9LXt43D RnH7IoSbdS6ZQ1uXmInjk6ouQQUZWhdMSCnjGUXvbHKS3GDa/syle8MzRVM0ApEM9T+p shmg+vnvEL8Y3gTTZaAwuEsuCoLa2WCkb/f8hTYYlm2vdC8H4lSaDxa6i+ShkCTd/hEo 4KxA== X-Gm-Message-State: AOAM5303zEVAGOH/4qQeRwP62l+vddtPZjGJJh6hxgeLYevD9c9VM5uD MivNME0JBOU/bY7iTCDqREOME/gXlvdhiaAeHU94GQd5N1HAAuXVIvvNHl+XKBIFYO5krI39kYj pKhEjl1FQsmI= X-Received: by 2002:a37:5289:: with SMTP id g131mr4833597qkb.26.1615414984862; Wed, 10 Mar 2021 14:23:04 -0800 (PST) X-Google-Smtp-Source: ABdhPJzAN3mDdBjKseLO5fmQHxuMXQeVPdNIXECiyhfVTWLlynM+To1wjlluNwci20PAJP2f7jI0tQ== X-Received: by 2002:a37:5289:: with SMTP id g131mr4833582qkb.26.1615414984522; Wed, 10 Mar 2021 14:23:04 -0800 (PST) Received: from xz-x1.redhat.com ([142.126.89.138]) by smtp.gmail.com with ESMTPSA id e18sm451364qtr.52.2021.03.10.14.23.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Mar 2021 14:23:04 -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 2/4] userfaultfd.2: Add write-protect mode Date: Wed, 10 Mar 2021 17:22:58 -0500 Message-Id: <20210310222300.200054-3-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: 55jkpfswdt9jxmx5ufrq4nitgs34b8sq X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 8DDB7E000106 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf21; 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: 1615414985-44872 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: Write-protect mode is supported starting from Linux 5.7. Signed-off-by: Peter Xu --- man2/userfaultfd.2 | 103 ++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 101 insertions(+), 2 deletions(-) diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 index 555e37409..d1f9aad24 100644 --- a/man2/userfaultfd.2 +++ b/man2/userfaultfd.2 @@ -78,6 +78,32 @@ all memory ranges that were registered with the object= are unregistered and unread events are flushed. .\" .PP +Userfaultfd supports two modes of registration: +.TP +.BR UFFDIO_REGISTER_MODE_MISSING " (since 4.10)" +When registered with +.B UFFDIO_REGISTER_MODE_MISSING +mode, the userspace will receive a page fault message when a missing pag= e is +accessed. +The faulted thread will be stopped from execution until the page fault i= s +resolved from the userspace by either an +.B UFFDIO_COPY +or an +.B UFFDIO_ZEROPAGE +ioctl. +.TP +.BR UFFDIO_REGISTER_MODE_WP " (since 5.7)" +When registered with +.B UFFDIO_REGISTER_MODE_WP +mode, the userspace will receive a page fault message when a write-prote= cted +page is written. +The faulted thread will be stopped from execution until the userspace +un-write-protect the page using an +.B UFFDIO_WRITEPROTECT +ioctl. +.PP +Multiple modes can be enabled at the same time for the same memory range= . +.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 @@ -144,6 +170,17 @@ single threaded non-cooperative userfaultfd manager = implementations. .\" and limitations remaining in 4.11 .\" Maybe it's worth adding a dedicated sub-section... .\" +.PP +Starting from Linux 5.7, userfaultfd is able to do synchronous page dirt= y +tracking using the new write-protection register mode. +One should check against the feature bit +.B UFFD_FEATURE_PAGEFAULT_FLAG_WP +before using this feature. +Similar to the original userfaultfd missing mode, the write-protect mode= will +generate an userfaultfd message when the protected page is written. +The user needs to resolve the page fault by unprotecting the faulted pag= e and +kick the faulted thread to continue. +For more information, please refer to "Userfaultfd write-protect mode" s= ection. .SS Userfaultfd operation After the userfaultfd object is created with .BR userfaultfd (), @@ -219,6 +256,64 @@ userfaultfd can be used only with anonymous private = memory mappings. Since Linux 4.11, userfaultfd can be also used with hugetlbfs and shared memory mappings. .\" +.SS Userfaultfd write-protect mode (since 5.7) +Since Linux 5.7, userfaultfd supports write-protect mode. +The user needs to first check availability of this feature using +.B UFFDIO_API +ioctl against the feature bit +.B UFFD_FEATURE_PAGEFAULT_FLAG_WP +before using this feature. +.PP +To register with userfaultfd write-protect mode, the user needs to initi= ate the +.B UFFDIO_REGISTER +ioctl with mode +.B UFFDIO_REGISTER_MODE_WP +set. +Note that it's legal to monitor the same memory range with multiple mode= s. +For example, the user can do +.B UFFDIO_REGISTER +with the mode set to +.BR "UFFDIO_REGISTER_MODE_MISSING | UFFDIO_REGISTER_MODE_WP" . +When there is only +.B UFFDIO_REGISTER_MODE_WP +registered, the userspace will +.I not +receive any message when a missing page is written. +Instead, the userspace will only receive a write-protect page fault mess= age +when an existing but write-protected page got written. +.PP +After the +.B UFFDIO_REGISTER +ioctl completed with +.B UFFDIO_REGISTER_MODE_WP +mode set, the user can write-protect any existing memory within the rang= e using +the ioctl +.B UFFDIO_WRITEPROTECT +where +.I uffdio_writeprotect.mode +should be set to +.BR UFFDIO_WRITEPROTECT_MODE_WP . +.PP +When a write-protect event happens, the userspace will receive a page fa= ult +message whose +.I uffd_msg.pagefault.flags +will be with +.B UFFD_PAGEFAULT_FLAG_WP +flag set. Note: since only writes can trigger such kind of fault, +write-protect messages will always be with +.B UFFD_PAGEFAULT_FLAG_WRITE +bit set too along with bit +.BR UFFD_PAGEFAULT_FLAG_WP . +.PP +To resolve a write-protection page fault, the user should initiate anoth= er +.B UFFDIO_WRITEPROTECT +ioctl, whose +.I uffd_msg.pagefault.flags +should have the flag +.B UFFDIO_WRITEPROTECT_MODE_WP +cleared upon the faulted page or range. +.PP +Write-protect mode only supports private anonymous memory. .SS Reading from the userfaultfd structure Each .BR read (2) @@ -364,8 +459,12 @@ flag (see .BR ioctl_userfaultfd (2)) and this flag is set, this a write fault; otherwise it is a read fault. -.\" -.\" UFFD_PAGEFAULT_FLAG_WP is not yet supported. +.TP +.B UFFD_PAGEFAULT_FLAG_WP +If the address is in a range that was registered with the +.B UFFDIO_REGISTER_MODE_WP +flag, when this bit is set it means it's a write-protect fault. Otherwi= se it's +a page missing fault. .RE .TP .I pagefault.feat.pid --=20 2.26.2