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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E70F5EB64DA for ; Wed, 14 Jun 2023 04:20:32 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 491466B0074; Wed, 14 Jun 2023 00:20:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 441426B0075; Wed, 14 Jun 2023 00:20:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 293966B0078; Wed, 14 Jun 2023 00:20:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 128D26B0074 for ; Wed, 14 Jun 2023 00:20:32 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id CE25316070E for ; Wed, 14 Jun 2023 04:20:31 +0000 (UTC) X-FDA: 80900051862.19.B3D4293 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf15.hostedemail.com (Postfix) with ESMTP id 186A8A0012 for ; Wed, 14 Jun 2023 04:20:29 +0000 (UTC) Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=ptry9IrR; spf=none (imf15.hostedemail.com: domain of rdunlap@infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=rdunlap@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1686716430; h=from:from:sender: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:dkim-signature; bh=D9e3x9i8rBKYm3toYXDRWUXq9796QOZEiqel4E9RDSQ=; b=kT1jhpRn2oSA9tsSz2wAAUf88cFdKTsTEkp5zBO8QErln8lWTy3bxXuJpxz3E7ydMUlXhJ IzI90xyaNYBWs9sMnVk82R/qSpUYhiOTJT5/IM8dccR2FH54Z9b8W5SoqhgQEuCnreKydH kBr5DUdMGDTEoFV8SIJSqapNIJQKHz8= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1686716430; a=rsa-sha256; cv=none; b=bvLcptGO8lhsX+U6PR8uTDkfyJu3w6ymNOxTXkUFTWjcxNNz9YkDX2aIjr5KMFWp33MMyz yy3YWVQs2EkHzoB9woB/J7SwfXt01IeFZqA1JzHMbcbU1gmBNWCH4RnF5SuteB6PPb29NJ MqywbCjTQH5zdGy2l5xqxzDbjUxdTPo= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=ptry9IrR; spf=none (imf15.hostedemail.com: domain of rdunlap@infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=rdunlap@infradead.org; dmarc=none DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Sender:Reply-To:Content-ID:Content-Description; bh=D9e3x9i8rBKYm3toYXDRWUXq9796QOZEiqel4E9RDSQ=; b=ptry9IrRJnz/Kqmd1+0osrL1CQ iSA86OAjUouPrH3MIaIdajDF8MeIKN16meKgjfkpQXUtlmG7+YfL6VwgPDRLPo2YUvfn4WZ4hGNI+ DzkxISScnE7H0Hm70ysbCXZkG6iQcxhJst84nH5UEwSVp4ZS/TyvG8/3/GnsTNa/Nu2+5EXlQruEz GAMeK7rfui/COGK3C8/0lpbQYHJB79vqlU7aK02zJhMrzjKLaMKyWXXTnhRilEDJMxPfkuiWHaDVX ED9HhmateLa2wPxWCmaSd08C2s/sflld2Y2YwrlC4Ss6MkQRCL/5T8TIGihDngwMXn5db+ottR/U6 aDuqAwpw==; Received: from [2601:1c2:980:9ec0::2764] by bombadil.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1q9HzO-009xON-2S; Wed, 14 Jun 2023 04:20:10 +0000 Message-ID: <57358041-0e36-deaa-e2ec-06dcfc92ba4d@infradead.org> Date: Tue, 13 Jun 2023 21:20:09 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.2 Subject: Re: [PATCH v18 4/5] mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL Content-Language: en-US To: Muhammad Usama Anjum , Peter Xu , David Hildenbrand , Andrew Morton , =?UTF-8?B?TWljaGHFgiBNaXJvc8WC?= =?UTF-8?Q?aw?= , Andrei Vagin , Danylo Mocherniuk , Paul Gofman , Cyrill Gorcunov , Mike Rapoport , Nadav Amit Cc: Alexander Viro , Shuah Khan , Christian Brauner , Yang Shi , Vlastimil Babka , "Liam R . Howlett" , Yun Zhou , Suren Baghdasaryan , Alex Sierra , Matthew Wilcox , Pasha Tatashin , Axel Rasmussen , "Gustavo A . R . Silva" , Dan Williams , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Greg KH , kernel@collabora.com References: <20230613102905.2808371-1-usama.anjum@collabora.com> <20230613102905.2808371-5-usama.anjum@collabora.com> From: Randy Dunlap In-Reply-To: <20230613102905.2808371-5-usama.anjum@collabora.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 186A8A0012 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: d61183j9ja6ou9nbioayc1gq59tf5zr9 X-HE-Tag: 1686716429-439579 X-HE-Meta: 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 iIRYeiFu dAm/LtwgM7Ia3sf24jhpX6prXwgFCWk0I6cSuAEdLzVmW1dIiRWvMBHeeZ5aIlclBnlTo4C/HHiNePw8lRH+fbZA+JZ+6b5rB+Fe19t7aXCbe72sr13y0vgY7jXmIy/xnrbOaRZGBeFCSFebOT/eNBp19zafXoRPBlc2pRnV6vjKLBXxA/H0/a/Bu9naBVtMFpWdg06EAhvqTHA1BvYj7uRpLI3bqudglYZZkGw9iggUY7dCb6+sL+Utdrx7evZ6zdoZQuhnrXxtta67rL1IKgTrTzbDBS3XFRviHuHE1atZjMI0F0fKxCGzJ8Q== 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: Hi-- On 6/13/23 03:29, Muhammad Usama Anjum wrote: > Add some explanation and method to use write-protection and written-to > on memory range. > > Signed-off-by: Muhammad Usama Anjum > --- > Changes in v16: > - Update the documentation > > Changes in v11: > - Add more documentation > --- > Documentation/admin-guide/mm/pagemap.rst | 58 ++++++++++++++++++++++++ > 1 file changed, 58 insertions(+) > > diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst > index c8f380271cad..3b977526d4b3 100644 > --- a/Documentation/admin-guide/mm/pagemap.rst > +++ b/Documentation/admin-guide/mm/pagemap.rst > @@ -227,3 +227,61 @@ Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is > always 12 at most architectures). Since Linux 3.11 their meaning changes > after first clear of soft-dirty bits. Since Linux 4.2 they are used for > flags unconditionally. > + > +Pagemap Scan IOCTL > +================== > + > +The ``PAGEMAP_SCAN`` IOCTL on the pagemap file can be used to get or optionally > +clear the info about page table entries. The following operations are supported > +in this IOCTL: > +- Get the information if the pages have been written-to (``PAGE_IS_WRITTEN``), written to > + file mapped (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``) or swapped > + (``PAGE_IS_SWAPPED``). > +- Find pages which have been written-to and/or write protect the pages atomically written to > + (atomic ``PM_SCAN_OP_GET + PM_SCAN_OP_WP``) > + > +The ``struct pm_scan_arg`` is used as the argument of the IOCTL. > + 1. The size of the ``struct pm_scan_arg`` must be specified in the ``size`` > + field. This field will be helpful in recognizing the structure if extensions > + are done later. > + 2. The flags can be specified in the ``flags`` field. The ``PM_SCAN_OP_GET`` > + and ``PM_SCAN_OP_WP`` are the only added flags at this time. > + 3. The range is specified through ``start`` and ``len``. > + 4. The output buffer of ``struct page_region`` array and size is specified in > + ``vec`` and ``vec_len``. > + 5. The optional maximum requested pages are specified in the ``max_pages``. > + 6. The masks are specified in ``required_mask``, ``anyof_mask``, > + ``excluded_ mask`` and ``return_mask``. > + 1. To find if ``PAGE_IS_WRITTEN`` flag is set for pages which have > + ``PAGE_IS_FILE`` set and ``PAGE_IS_SWAPPED`` un-set, ``required_mask`` unset, > + is set to ``PAGE_IS_FILE``, ``exclude_mask`` is set to > + ``PAGE_IS_SWAPPED`` and ``return_mask`` is set to ``PAGE_IS_WRITTEN``. > + The output buffer in ``vec`` and length must be specified in ``vec_len``. > + 2. To find pages which have either ``PAGE_IS_FILE`` or ``PAGE_IS_SWAPPED`` > + set, ``anyof_masks`` is set to ``PAGE_IS_FILE | PAGE_IS_SWAPPED``. > + 3. To find written pages and engage write protect, ``PAGE_IS_WRITTEN`` is > + specified in ``required_mask`` and ``return_mask``. In addition to > + specifying the output buffer in ``vec`` and length in ``vec_len``, the > + ``PM_SCAN_OP_WP`` is specified in ``flags`` to perform write protect > + on the range as well. > + > +The ``PAGE_IS_WRITTEN`` flag can be considered as the better and correct > +alternative of soft-dirty flag. It doesn't get affected by household chores (VMA housekeeping ? > +merging) of the kernel and hence the user can find the true soft-dirty pages > +only. This IOCTL adds the atomic way to find which pages have been written and > +write protect those pages again. This kind of operation is needed to efficiently > +find out which pages have changed in the memory. > + > +To get information about which pages have been written-to or optionally write written to > +protect the pages, following must be performed first in order: > + 1. The userfaultfd file descriptor is created with ``userfaultfd`` syscall. > + 2. The ``UFFD_FEATURE_WP_UNPOPULATED`` and ``UFFD_FEATURE_WP_ASYNC`` features > + are set by ``UFFDIO_API`` IOCTL. > + 3. The memory range is registered with ``UFFDIO_REGISTER_MODE_WP`` mode > + through ``UFFDIO_REGISTER`` IOCTL. > + 4. Then the any part of the registered memory or the whole memory region must "the" or "any". Probably "any". Not both. > + be write protected using ``PAGEMAP_SCAN`` IOCTL with flag ``PM_SCAN_OP_WP`` > + or the ``UFFDIO_WRITEPROTECT`` IOCTL can be used. Both of these perform the > + same operation. The former is better in terms of performance. > + 5. Now the ``PAGEMAP_SCAN`` IOCTL can be used to either just find pages which > + have been written-to and/or optionally write protect the pages as well. written to -- ~Randy