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 C393AEB64D7 for ; Wed, 21 Jun 2023 07:03:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231139AbjFUHDV (ORCPT ); Wed, 21 Jun 2023 03:03:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48446 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230011AbjFUHDA (ORCPT ); Wed, 21 Jun 2023 03:03:00 -0400 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 D28061706; Wed, 21 Jun 2023 00:02:58 -0700 (PDT) Received: from [192.168.10.54] (unknown [119.155.63.248]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) (Authenticated sender: usama.anjum) by madras.collabora.co.uk (Postfix) with ESMTPSA id 4FAA76606F53; Wed, 21 Jun 2023 08:02:50 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1687330977; bh=4zCIr0nvtkxqnHDb33CDUF+eZAo3KpOgtTvlUQMRH4s=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=LhFqo2R4ekMCMbK8KGAN+/1chKfL4dQnXPZ2PNnSBNfNs9YcMcyM35d9PR/QVaVS6 UzSCaqmoNxu+FQHH+pd1yUdUWQC9zS6WESdMiRx49WnYVD3JbzieoMdit7+5eHOUaG 5ZpcrybkUpQ0gM6n0rVDJUp/Mb8rcP/MQKSxtTHrUT+2V9el762YoHUkIDvytTEWJ/ F+7dQ1xtLSi0sqHgF71p+oZhnRmiAUbP44ZmmqLVD6DCVsUI7CABQJMEXiWFh5oVJu 3wboyArYZUkeGt0p4Z8cqg8EHWY4eSLfsS4Piyfc7faitrZYIlsr6xVpnGoYTYkGWU oYC6FAd+ndyXw== Message-ID: <9af9a116-cab4-be02-4616-f809291f46e7@collabora.com> Date: Wed, 21 Jun 2023 12:02:46 +0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Cc: Muhammad Usama Anjum , Peter Xu , David Hildenbrand , Andrew Morton , =?UTF-8?B?TWljaGHFgiBNaXJvc8WC?= =?UTF-8?Q?aw?= , Danylo Mocherniuk , Paul Gofman , Cyrill Gorcunov , Mike Rapoport , Nadav Amit , 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 Subject: Re: [PATCH v19 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs Content-Language: en-US To: Andrei Vagin References: <20230615141144.665148-1-usama.anjum@collabora.com> <20230615141144.665148-3-usama.anjum@collabora.com> <212e331f-35b0-5ae7-6371-26caa577d637@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 6/21/23 11:42 AM, Andrei Vagin wrote: > On Mon, Jun 19, 2023 at 11:06:36AM +0500, Muhammad Usama Anjum wrote: >> On 6/17/23 11:39 AM, Andrei Vagin wrote: >>> On Thu, Jun 15, 2023 at 07:11:41PM +0500, Muhammad Usama Anjum wrote: >>>> +static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start, >>>> + unsigned long end, struct mm_walk *walk) >>>> +{ >>>> + bool is_written, flush = false, is_interesting = true; >>>> + struct pagemap_scan_private *p = walk->private; >>>> + struct vm_area_struct *vma = walk->vma; >>>> + unsigned long bitmap, addr = end; >>>> + pte_t *pte, *orig_pte, ptent; >>>> + spinlock_t *ptl; >>>> + int ret = 0; >>>> + >>>> + arch_enter_lazy_mmu_mode(); >>>> + >>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE >>>> + ptl = pmd_trans_huge_lock(pmd, vma); >>>> + if (ptl) { >>>> + unsigned long n_pages = (end - start)/PAGE_SIZE; >>>> + >>>> + if (p->max_pages && n_pages > p->max_pages - p->found_pages) >>>> + n_pages = p->max_pages - p->found_pages; >>>> + >>>> + is_written = !is_pmd_uffd_wp(*pmd); >>>> + >>>> + /* >>>> + * Break huge page into small pages if the WP operation need to >>>> + * be performed is on a portion of the huge page. >>>> + */ >>>> + if (is_written && IS_PM_SCAN_WP(p->flags) && >>>> + n_pages < HPAGE_SIZE/PAGE_SIZE) { >>>> + spin_unlock(ptl); >>>> + >>>> + split_huge_pmd(vma, pmd, start); >>>> + goto process_smaller_pages; >>>> + } >>>> + >>>> + bitmap = PM_SCAN_FLAGS(is_written, (bool)vma->vm_file, >>>> + pmd_present(*pmd), is_swap_pmd(*pmd)); >>>> + >>>> + if (IS_PM_SCAN_GET(p->flags)) { >>>> + is_interesting = pagemap_scan_is_interesting_page(bitmap, p); >>>> + if (is_interesting) >>>> + ret = pagemap_scan_output(bitmap, p, start, n_pages); >>>> + } >>>> + >>>> + if (IS_PM_SCAN_WP(p->flags) && is_written && is_interesting && >>>> + ret >= 0) { >>>> + make_uffd_wp_pmd(vma, start, pmd); >>>> + flush_tlb_range(vma, start, end); >>>> + } >>>> + >>>> + spin_unlock(ptl); >>>> + >>>> + arch_leave_lazy_mmu_mode(); >>>> + return ret; >>>> + } >>>> + >>>> +process_smaller_pages: >>>> +#endif >>>> + >>>> + orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl); >>>> + if (!pte) { >>> >>> Do we need to unlock ptl here? >>> >>> spin_unlock(ptl); >> No, please look at these recently merged patches: >> https://lore.kernel.org/all/c1c9a74a-bc5b-15ea-e5d2-8ec34bc921d@google.com >> >>> >>>> + walk->action = ACTION_AGAIN; >>>> + return 0; >>>> + } >>>> + >>>> + for (addr = start; addr < end && !ret; pte++, addr += PAGE_SIZE) { >>>> + ptent = ptep_get(pte); >>>> + is_written = !is_pte_uffd_wp(ptent); >>>> + >>>> + bitmap = PM_SCAN_FLAGS(is_written, (bool)vma->vm_file, >>>> + pte_present(ptent), is_swap_pte(ptent)); >>> >>> The vma->vm_file check isn't correct in this case. You can look when >>> pte_to_pagemap_entry sets PM_FILE. This flag is used to detect what >>> pages have a file backing store and what pages are anonymous. >> I'll update. >> >>> >>> I was trying to integrate this new interace into CRIU and I found >>> one more thing that is required. We need to detect zero pages. >> Should we name it ZERO_PFN_PRESENT_PAGE to be exact or what? > > IMHO, ZERO_PFN_PRESENT_PAGE looks a bit monstrous. > It looks like zero page is a proper noun in the kernel, so PAGE_IS_ZERO > might be a good choice here, but it is up to you. > >> >>> >>> It should look something like this: >>> >>> #define PM_SCAN_FLAGS(wt, file, present, swap, zero) \ >>> ((wt) | ((file) << 1) | ((present) << 2) | ((swap) << 3) | ((zero) << 4)) >>> >>> >>> bitmap = PM_SCAN_FLAGS(is_written, page && !PageAnon(page), >>> pte_present(ptent), is_swap_pte(ptent), >>> pte_present(ptent) && is_zero_pfn(pte_pfn(ptent))); >> Okay. Can you please confirm my assumptions: >> - A THP cannot be file backed. (PM_FILE isn't being set for THP case) > > ``` > Currently THP only works for anonymous memory mappings and tmpfs/shmem. > But in the future it can expand to other filesystems. > ``` > https://www.kernel.org/doc/html/next/admin-guide/mm/transhuge.html > > so THP can be "file backed". > >> - A hole is also not file backed. >> >> A hole isn't present in memory. So its pfn would be zero. But as it isn't >> present, it shouldn't report zero page. Right? For hole:: >> >> PM_SCAN_FLAGS(false, false, false, false, false) > > This looks correct to me. Thanks. I'll sent next version in a few minutes. > -- BR, Muhammad Usama Anjum