From patchwork Tue Aug 8 10:43:08 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Muhammad Usama Anjum X-Patchwork-Id: 13345955 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 26B98C001DF for ; Tue, 8 Aug 2023 10:43:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BD1188D0001; Tue, 8 Aug 2023 06:43:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B5AA76B007E; Tue, 8 Aug 2023 06:43:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9AD178D0001; Tue, 8 Aug 2023 06:43:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 898AF6B007D for ; Tue, 8 Aug 2023 06:43:57 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 58F171204FE for ; Tue, 8 Aug 2023 10:43:57 +0000 (UTC) X-FDA: 81100602114.19.C4923F7 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by imf14.hostedemail.com (Postfix) with ESMTP id 80B1F100005 for ; Tue, 8 Aug 2023 10:43:55 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=k0FKLCXq; spf=pass (imf14.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com; dmarc=pass (policy=quarantine) header.from=collabora.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1691491435; 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-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=vQEABLOiYASfKGN+kJcFTbE8TxJb5utgEVWNwJV3QQM=; b=uhLjWUT7LvIiX8cbZ9MfkieLmykroDdlHrjXGl43rorj3EFxvXCPLb2R5uc4fy6j3q6D/n 6AyluE6yo+zBq4aeyNir5PlsYJZAg2AJ5n3dR0h3ZmKoLB/BGy6HZymfZPDBJf+p+LUtWw rdovLaEJSWvdXtGZhxthZkrdc0p6IcA= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1691491435; a=rsa-sha256; cv=none; b=JJVfCAFQHKSVFZwGM5S82HrMp46EOlbE107bowREkxD9Z1eGcHEx3rEjHL1RdUDbuSl6C0 mAcpiO5rwm1okWdEyPfvHviQXMU2+Ik1S1CtgG0mz2mHr4J5REhm7HAQ8kzVq04+1tCEzg AJyqqar3dg3NfUs3EPEZn2ONj9RCPo8= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=k0FKLCXq; spf=pass (imf14.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com; dmarc=pass (policy=quarantine) header.from=collabora.com Received: from localhost.localdomain (unknown [59.103.218.230]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: usama.anjum) by madras.collabora.co.uk (Postfix) with ESMTPSA id 949086607203; Tue, 8 Aug 2023 11:43:48 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1691491434; bh=Mo1XH1UBRenLTz5BwK9wfXpLgt7ICRwepxhynxV74M4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=k0FKLCXqy5zalIsSNo963PsSTgeTYuU9myTG4EXy/smDd6h3Bs8gvz+BjsChLuog/ v14FIXSSfpqWpzkT1tpzFBYLkEOXCYMwHCVXlAyv6iJFt1LXnqhqx+hf2HhPIVFJiB A94AjQlxHmHkv4TirftQqzzZObq1ySDs7aRcvLBURg5uRXE329fpfroJZWvrbzBFdC 7DeUPSjwy642Hl1lCfa4jh++YjM/xGLcrhM42akTIMgA439oyY9QRPFOboAW/dRhI0 gS9hzvbBTV1wlOOCoupQYMittCndBzhL89GgLAsVK/4ET5K9expMuwmYbuIqRj7LiH q2Zm0XOLtAICA== From: Muhammad Usama Anjum To: Peter Xu , David Hildenbrand , Andrew Morton , =?utf-8?b?TWljaGHFgiBNaXJvc8WC?= =?utf-8?b?YXc=?= , 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 , Muhammad Usama Anjum , 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 Subject: [PATCH v27 5/6] mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL Date: Tue, 8 Aug 2023 15:43:08 +0500 Message-Id: <20230808104309.357852-6-usama.anjum@collabora.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230808104309.357852-1-usama.anjum@collabora.com> References: <20230808104309.357852-1-usama.anjum@collabora.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: 80B1F100005 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: iazy3rh59yhq3adqj8p1os59wk6y9ea6 X-HE-Tag: 1691491435-46954 X-HE-Meta: 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 mb8vK0Lv uCG75ik37FiN7l1qfZ3Tj/Yok58i2Eu3MM1zszwpAqNlkSIc0AUZbi7x5sK1x8qRSpRr77BzAWlA5A6tZ5IWuYU7uCljAllUsKffOoBsl1RqiJ8sLZ5JeSJJnAwRoTqIzo7Ve4tCenaz52m8dwvRaM8O4LSY7nJlG7DEQT6V+D211hyufaH8okjDSPTl7IZQMNCU41tMcd5Jg0dTAbPuRNPEBSKZ0bmVLjoO8K4ZR2UI6bWjDZ21Lf02NI9fI7GTHhPzpkzbmRUPtPlMs8uV/VqJbYWIh6aOzHVgAsNG2eQ7wueY= 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: Add some explanation and method to use write-protection and written-to on memory range. Signed-off-by: Muhammad Usama Anjum --- Changes in v26: - Update documentation according to latest revision Changes in v21: - Update according to changed interface Changes in v20: - Add new flag in documentation Changes in v19: - Improved documentatiom with punctuation marks Changes in v16: - Update the documentation Changes in v11: - Add more documentation --- Documentation/admin-guide/mm/pagemap.rst | 64 ++++++++++++++++++++++++ 1 file changed, 64 insertions(+) diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst index c8f380271cad8..ea18e4575902a 100644 --- a/Documentation/admin-guide/mm/pagemap.rst +++ b/Documentation/admin-guide/mm/pagemap.rst @@ -227,3 +227,67 @@ 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 Async Write-Protection enabled + (``PAGE_IS_WPALLOWED``), have been written to (``PAGE_IS_WRITTEN``), file mapped + (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``), swapped (``PAGE_IS_SWAPPED``) + or page has pfn zero (``PAGE_IS_PFNZERO``). +- Find pages which have been written to and/or write protect + (atomic ``PM_SCAN_WP_MATCHING + PM_SCAN_CHECK_WPASYNC``) the pages atomically. + The (``PM_SCAN_WP_MATCHING``) is used to WP the matched pages. The + (``PM_SCAN_CHECK_WPASYNC``) aborts the operation if non-Async-Write-Protected + pages are found. + +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_WP_MATCHING`` + and ``PM_SCAN_CHECK_WPASYNC`` are the only added flags at this time. The get + operation is optionally performed depending upon if the output buffer is + provided or not. + 3. The range is specified through ``start`` and ``end``. + 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 ``category_mask``, ``category_anyof_mask``, + ``category_inverted`` 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`` unset, ``category_mask`` + is set to ``PAGE_IS_FILE | PAGE_IS_SWAPPED``, ``category_inverted`` 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, ``category_anyof_mask`` is set to ``PAGE_IS_FILE | PAGE_IS_SWAPPED``. + 3. To find written pages and engage write protect, ``PAGE_IS_WRITTEN`` is + specified in ``category_mask`` and ``return_mask``. In addition to + specifying the output buffer in ``vec`` and length in ``vec_len``, the + ``PM_SCAN_WP_MATCHING`` 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 housekeeping chores +(VMA 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 +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 any part of the registered memory or the whole memory region must + 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.