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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 14CA8CDB47E for ; Wed, 18 Oct 2023 21:35:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229552AbjJRVfc (ORCPT ); Wed, 18 Oct 2023 17:35:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51586 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235220AbjJRVfa (ORCPT ); Wed, 18 Oct 2023 17:35:30 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4DF421B6 for ; Wed, 18 Oct 2023 14:35:13 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34EFEC433CD; Wed, 18 Oct 2023 21:34:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1697664897; bh=LXRF5wcCz6MinAuL8LRT0qNq5qN5lFayZAmkV+hhEz8=; h=Date:To:From:Subject:From; b=I7lxIP39hRLahDuXZP6Mb8hYdcbVhSGKtixY7XYvl+Pydcbr3TQZaS2vgujnIWNSU r0wrG4veHu9UxpjiCxsDal9wWYqU0Xkt1+u0XSIKRGaVH6805nSlWhhJ8UDxMrp4Hl S1OOiPoohOWlm5v5ZpAiDnQyRCvcDhaGlMWEeC0s= Date: Wed, 18 Oct 2023 14:34:56 -0700 To: mm-commits@vger.kernel.org, yun.zhou@windriver.com, willy@infradead.org, viro@zeniv.linux.org.uk, vbabka@suse.cz, surenb@google.com, shy828301@gmail.com, shuah@kernel.org, rppt@kernel.org, pgofman@codeweavers.com, peterx@redhat.com, pasha.tatashin@soleen.com, namit@vmware.com, mirq-linux@rere.qmqm.pl, Liam.Howlett@oracle.com, gustavoars@kernel.org, gregkh@linuxfoundation.org, gorcunov@gmail.com, emmir@google.com, david@redhat.com, dan.j.williams@intel.com, brauner@kernel.org, axelrasmussen@google.com, avagin@gmail.com, alex.sierra@amd.com, usama.anjum@collabora.com, akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-stable] mm-pagemap-add-documentation-of-pagemap_scan-ioctl.patch removed from -mm tree Message-Id: <20231018213457.34EFEC433CD@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The quilt patch titled Subject: mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL has been removed from the -mm tree. Its filename was mm-pagemap-add-documentation-of-pagemap_scan-ioctl.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Muhammad Usama Anjum Subject: mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL Date: Mon, 21 Aug 2023 19:15:17 +0500 Add some explanation and method to use write-protection and written-to on memory range. Link: https://lkml.kernel.org/r/20230821141518.870589-6-usama.anjum@collabora.com Signed-off-by: Muhammad Usama Anjum Cc: Alex Sierra Cc: Al Viro Cc: Andrei Vagin Cc: Axel Rasmussen Cc: Christian Brauner Cc: Cyrill Gorcunov Cc: Dan Williams Cc: David Hildenbrand Cc: Greg Kroah-Hartman Cc: Gustavo A. R. Silva Cc: "Liam R. Howlett" Cc: Matthew Wilcox Cc: Michal Miroslaw Cc: Michał Mirosław Cc: Mike Rapoport (IBM) Cc: Nadav Amit Cc: Pasha Tatashin Cc: Paul Gofman Cc: Peter Xu Cc: Shuah Khan Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Yang Shi Cc: Yun Zhou Signed-off-by: Andrew Morton --- Documentation/admin-guide/mm/pagemap.rst | 89 +++++++++++++++++++++ 1 file changed, 89 insertions(+) --- a/Documentation/admin-guide/mm/pagemap.rst~mm-pagemap-add-documentation-of-pagemap_scan-ioctl +++ a/Documentation/admin-guide/mm/pagemap.rst @@ -227,3 +227,92 @@ Before Linux 3.11 pagemap bits 55-60 wer 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: + +- Scan the address range and get the memory ranges matching the provided criteria. + This is performed when the output buffer is specified. +- Write-protect the pages. The ``PM_SCAN_WP_MATCHING`` is used to write-protect + the pages of interest. The ``PM_SCAN_CHECK_WPASYNC`` aborts the operation if + non-Async Write Protected pages are found. The ``PM_SCAN_WP_MATCHING`` can be + used with or without ``PM_SCAN_CHECK_WPASYNC``. +- Both of those operations can be combined into one atomic operation where we can + get and write protect the pages as well. + +Following flags about pages are currently supported: + +- ``PAGE_IS_WPALLOWED`` - Page has async-write-protection enabled +- ``PAGE_IS_WRITTEN`` - Page has been written to from the time it was write protected +- ``PAGE_IS_FILE`` - Page is file backed +- ``PAGE_IS_PRESENT`` - Page is present in the memory +- ``PAGE_IS_SWAPPED`` - Page is in swapped +- ``PAGE_IS_PFNZERO`` - Page has zero PFN +- ``PAGE_IS_HUGE`` - Page is THP or Hugetlb backed + +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 walk can abort before visiting the complete range such as the user buffer + can get full etc. The walk ending address is specified in``end_walk``. + 5. The output buffer of ``struct page_region`` array and size is specified in + ``vec`` and ``vec_len``. + 6. The optional maximum requested pages are specified in the ``max_pages``. + 7. The masks are specified in ``category_mask``, ``category_anyof_mask``, + ``category_inverted`` and ``return_mask``. + +Find pages which have been written and WP them as well:: + + struct pm_scan_arg arg = { + .size = sizeof(arg), + .flags = PM_SCAN_CHECK_WPASYNC | PM_SCAN_CHECK_WPASYNC, + .. + .category_mask = PAGE_IS_WRITTEN, + .return_mask = PAGE_IS_WRITTEN, + }; + +Find pages which have been written, are file backed, not swapped and either +present or huge:: + + struct pm_scan_arg arg = { + .size = sizeof(arg), + .flags = 0, + .. + .category_mask = PAGE_IS_WRITTEN | PAGE_IS_SWAPPED, + .category_inverted = PAGE_IS_SWAPPED, + .category_anyof_mask = PAGE_IS_PRESENT | PAGE_IS_HUGE, + .return_mask = PAGE_IS_WRITTEN | PAGE_IS_SWAPPED | + PAGE_IS_PRESENT | PAGE_IS_HUGE, + }; + +The ``PAGE_IS_WRITTEN`` flag can be considered as a better-performing alternative +of soft-dirty flag. It doesn't get affected by VMA merging of the kernel and hence +the user can find the true soft-dirty pages in case of normal pages. (There may +still be extra dirty pages reported for THP or Hugetlb pages.) + +"PAGE_IS_WRITTEN" category is used with uffd write protect-enabled ranges to +implement memory dirty tracking in userspace: + + 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_WP_MATCHING`` + 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 since they were last marked and/or optionally write protect + the pages as well. _ Patches currently in -mm which might be from usama.anjum@collabora.com are