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=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 AA379C433E6 for ; Wed, 10 Mar 2021 21:47:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6C28C64FCE for ; Wed, 10 Mar 2021 21:47:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232106AbhCJVrG (ORCPT ); Wed, 10 Mar 2021 16:47:06 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:40358 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231221AbhCJVqn (ORCPT ); Wed, 10 Mar 2021 16:46:43 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615412802; 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: in-reply-to:in-reply-to:references:references; bh=/4BAvAYb0p56VURUt0aneYd5tRaSp4726siIe8mGwLs=; b=hrbdYuYlAfjS1NRSbqxSDM9De1BOFaVEiyq0w6OvfgTuz7h0qjKh/RSw9s1+YK7s0vV+w7 9cvDWVvPwm7gbFpZSU002ORLf2hBOoRxJ7sCuh9OM/Y5vnLN0g2SIkr80e8qlwlaSCmVwo oFLQtDgNiXq8JINUqPyLnXpuTPRQe7U= Received: from mail-qv1-f71.google.com (mail-qv1-f71.google.com [209.85.219.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-501-6gNMjfExOm-TlpTTD46FhA-1; Wed, 10 Mar 2021 16:46:40 -0500 X-MC-Unique: 6gNMjfExOm-TlpTTD46FhA-1 Received: by mail-qv1-f71.google.com with SMTP id dz17so13703982qvb.14 for ; Wed, 10 Mar 2021 13:46:40 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=/4BAvAYb0p56VURUt0aneYd5tRaSp4726siIe8mGwLs=; b=bi0PuJHLtNEUXH2F7INlixcDvcbyn5ZO9RFpPTbgziXe3eK5yoCb1o76lMjX96nrjy syqUccOntdfCkPbvLtEPLNlMNilnESmNhKj7rWnw3OHFU9xAx1FAOcrpekLHsDLxzX7G VRaVTlSKuu54jT/68L4ZgPGMt6ABTf8yPl7fisr0bcfwuc4FCDCr1ZogX8l4PjUZQp3Q yd1blNrj9IAaLf/s4zBi+uEylEAfpvEG4jbj76hT4/OITewqNWqE9vqold/cw4DJ6Bfp tTlR7Tw+dLiiBPT3beftFl2LMgwmd3zPKEFtPpPrGxBu+UvWQeD2PEkzEZgOxoniG7wq 5GnA== X-Gm-Message-State: AOAM532MvFkMYk9w98DuXFXv83S9QcIAn4KYpsdTBK1rrjl/21boNovQ gMyftbrRnEzeMNmiXoW+kHrWAzmfWF4eM2OSGLzAzvsGy2YA7IQYQ6jjuGdKBov6m07AHb61EoM EEC2666geo2mToDx846p+AJFG X-Received: by 2002:a05:6214:194f:: with SMTP id q15mr5148356qvk.46.1615412800305; Wed, 10 Mar 2021 13:46:40 -0800 (PST) X-Google-Smtp-Source: ABdhPJzNyEKmeMSTe/8AHX91In05+hEnDecNNNxFfngMdnwhuXY0MXGy87XhxBOkq6T5f0r9VUyHQA== X-Received: by 2002:a05:6214:194f:: with SMTP id q15mr5148336qvk.46.1615412799955; Wed, 10 Mar 2021 13:46:39 -0800 (PST) Received: from xz-x1 ([142.126.89.138]) by smtp.gmail.com with ESMTPSA id a14sm384686qtw.80.2021.03.10.13.46.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Mar 2021 13:46:39 -0800 (PST) Date: Wed, 10 Mar 2021 16:46:38 -0500 From: Peter Xu To: "Alejandro Colomar (man-pages)" Cc: linux-man@vger.kernel.org, Nadav Amit , Andrea Arcangeli , linux-kernel@vger.kernel.org, Michael Kerrisk , Mike Rapoport , Axel Rasmussen , Andrew Morton , Linux MM Mailing List Subject: Re: [PATCH v2 2/4] userfaultfd.2: Add write-protect mode Message-ID: <20210310214638.GA194839@xz-x1> References: <20210304163140.543171-1-peterx@redhat.com> <20210304163140.543171-3-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 10, 2021 at 08:16:24PM +0100, Alejandro Colomar (man-pages) wrote: > Hi Peter, > > Please see a few comments below. > > Thanks, > > Alex > > On 3/4/21 5:31 PM, Peter Xu wrote: > > Write-protect mode is supported starting from Linux 5.7. > > > > Signed-off-by: Peter Xu > > --- > > man2/userfaultfd.2 | 98 +++++++++++++++++++++++++++++++++++++++++++++- > > 1 file changed, 96 insertions(+), 2 deletions(-) > > > > diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 > > index 0cd426a8a..426307bcf 100644 > > --- a/man2/userfaultfd.2 > > +++ b/man2/userfaultfd.2 > > @@ -78,6 +78,30 @@ all memory ranges that were registered with the object are unregistered > > and unread events are flushed. > > .\" > > .PP > > +Currently, userfaultfd supports two modes of registration: > > "Currently" > > Than word is quite unstable and unprecise. > I think it would be better to use an absolute reference, such as "Since > Linux x.y, ...". I decided to remove the "Currently" and put the "(since x.y)" into each mode: diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 index 426307bcf..1132f52a3 100644 --- a/man2/userfaultfd.2 +++ b/man2/userfaultfd.2 @@ -78,9 +78,9 @@ all memory ranges that were registered with the object are unregistered and unread events are flushed. .\" .PP -Currently, userfaultfd supports two modes of registration: +Userfaultfd supports two modes of registration: .TP -.B UFFDIO_REGISTER_MODE_MISSING +.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 page is @@ -91,7 +91,7 @@ or an .B UFFDIO_ZEROPAGE ioctl. .TP -.B UFFDIO_REGISTER_MODE_WP +.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-protected > > > +.TP > > +.B UFFDIO_REGISTER_MODE_MISSING > > +When registered with > > +.B UFFDIO_REGISTER_MODE_MISSING > > +mode, the userspace will receive a page fault message when a missing page is > > +accessed. The faulted thread will be stopped from execution until the page > > +fault is resolved from the userspace by either an > > +.B UFFDIO_COPY > > +or an > > +.B UFFDIO_ZEROPAGE > > +ioctl. > > +.TP > > +.B UFFDIO_REGISTER_MODE_WP > > +When registered with > > +.B UFFDIO_REGISTER_MODE_WP > > +mode, the userspace will receive a page fault message when a write-protected > > +page is written. The faulted thread will be stopped from execution until the > > Please, use "semantic newlines". > > $ man 7 man-pages |sed -n '/semantic newlines/,/^$/p' > Use semantic newlines > In the source of a manual page, new sentences should be > started on new lines, and long sentences should split into > lines at clause breaks (commas, semicolons, colons, and so > on). This convention, sometimes known as "semantic new- > lines", makes it easier to see the effect of patches, which > often operate at the level of individual sentences or sen- > tence clauses. Will do. > > > > > +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 faulting > > thread ID information into the fault message. One needs to enable this feature > > explicitly using the > > @@ -144,6 +168,16 @@ 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 dirty > > +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 page and kick the faulted thread to continue. For more information, > > +please read the "Userfaultfd write-protect mode" section below. > > .SS Userfaultfd operation > > After the userfaultfd object is created with > > .BR userfaultfd (), > > @@ -219,6 +253,62 @@ 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 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 > > +.BR UFFD_FEATURE_PAGEFAULT_FLAG_WP . > > +.PP > > +To register with userfaultfd write-protect mode, the user needs to initiate 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 > > +modes. For example, the user can do > > +.B UFFDIO_REGISTER > > +with the mode set to > > +.BR UFFDIO_REGISTER_MODE_MISSING\ |\ UFFDIO_REGISTER_MODE_WP . > > Please use quotes when possible: > > .BR "asdasd asdsadf dfgsdfg dsf" . Fixed. > > > +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 message 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 range 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 fault > > +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 > > +.BR UFFD_PAGEFAULT_FLAG_WP . > > +.PP > > +To resolve a write-protection page fault, the user should initiate another > > +.B UFFDIO_WRITEPROTECT > > +ioctl whose > > +.I uffd_msg.pagefault.flags > > +should have the flag > > +.BR UFFDIO_WRITEPROTECT_MODE_WP > > .B Fixed. Thanks, -- Peter Xu