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 01C15C636D4 for ; Mon, 13 Feb 2023 10:46:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229505AbjBMKqo (ORCPT ); Mon, 13 Feb 2023 05:46:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49648 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229851AbjBMKq0 (ORCPT ); Mon, 13 Feb 2023 05:46:26 -0500 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9BD1017CE6; Mon, 13 Feb 2023 02:45:56 -0800 (PST) Received: from [192.168.10.12] (unknown [39.45.179.179]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 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 52B43660210A; Mon, 13 Feb 2023 10:44:53 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1676285100; bh=rFkR6He2/D7jQAmT+MR3vtWZDzSsN2bw42gGtGr6rVg=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=DkbzWwYhAeY8Fk994zFJ9wdOCf6fh4VbSbfaGFd+KnglkqtWyNTpCG3nUy4+Wwzxf ql7ZNTdPN6jsOIFVpIqvT0KD/diMMHPupvPM7y3WBaiJje7xAO03ZBmidGzFOrA18s 7fgmPgLtrQAkfjthYcyWCMRkHCw3k1SoBytBa/fz+wdAHs6o6iJbLPwaaIKdDmW3VL oFM943VJWOS0IpZDvwLbHaJhbrceTDF0dQu1lGm4Pq2dljtZOY8KcmJKFgN6gq58mb 1HQMRZ4rPbyUHn6ragP+qxa/Dycyu9MuvHCK0zJQn9r3oBE4tzojh0ki07JY+7g+JX 61rJmBeKnE+wg== Message-ID: <83382901-6d0b-b38f-27cd-3a45259eee85@collabora.com> Date: Mon, 13 Feb 2023 15:44:48 +0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Cc: Muhammad Usama Anjum , David Hildenbrand , Andrew Morton , =?UTF-8?B?TWljaGHFgiBNaXJvc8WC?= =?UTF-8?Q?aw?= , Andrei Vagin , Danylo Mocherniuk , Paul Gofman , Cyrill Gorcunov , Alexander Viro , Shuah Khan , Christian Brauner , Yang Shi , Vlastimil Babka , "Liam R . Howlett" , Yun Zhou , Suren Baghdasaryan , Alex Sierra , Matthew Wilcox , Pasha Tatashin , Mike Rapoport , Nadav Amit , 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: Re: [PATCH v10 5/6] mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL Content-Language: en-US To: Peter Xu References: <20230202112915.867409-1-usama.anjum@collabora.com> <20230202112915.867409-6-usama.anjum@collabora.com> From: Muhammad Usama Anjum In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/10/23 12:26 AM, Peter Xu wrote: > On Thu, Feb 02, 2023 at 04:29:14PM +0500, 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 >> --- >> Documentation/admin-guide/mm/pagemap.rst | 24 ++++++++++++++++++++++++ >> 1 file changed, 24 insertions(+) >> >> diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst >> index 6e2e416af783..1cb2189e9a0d 100644 >> --- a/Documentation/admin-guide/mm/pagemap.rst >> +++ b/Documentation/admin-guide/mm/pagemap.rst >> @@ -230,3 +230,27 @@ 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 and/or 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``), >> + file mapped (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``) or swapped >> + (``PAGE_IS_SWAPPED``). >> +- Write-protect the pages (``PAGEMAP_WP_ENGAGE``) to start finding which >> + pages have been written-to. >> +- Find pages which have been written-to and write protect the pages >> + (atomic ``PAGE_IS_WRITTEN + PAGEMAP_WP_ENGAGE``) > > Could we extend this section a bit more? Some points for reference: > > - The new struct you introduced, definitions of each of the fields, and > generic use cases for each of the field/ops. > > - It'll be nice to list the OPs the new interface supports (GET, > WP_ENGAGE, GET+WP_ENGAGE). > > - When should people use this rather than the old pagemap interface? > What's the major problems to solve / what's the major difference? > (Maybe nice to reference the Windows API too here) I'll update the documentation. > >> + >> +To get information about which pages have been written-to and/or 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_ASYNC`` feature is set by ``UFFDIO_API`` IOCTL. >> + 3. The memory range is registered with ``UFFDIO_REGISTER_MODE_WP`` mode >> + through ``UFFDIO_REGISTER`` IOCTL. >> +Then the any part of the registered memory or the whole memory region can be >> +write protected using the ``UFFDIO_WRITEPROTECT`` IOCTL or ``PAGEMAP_SCAN`` >> +IOCTL. > > This part looks good. > > Thanks, > -- BR, Muhammad Usama Anjum