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 EE35FEB64DC for ; Tue, 27 Jun 2023 14:37:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231588AbjF0OhZ (ORCPT ); Tue, 27 Jun 2023 10:37:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38996 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231621AbjF0OhP (ORCPT ); Tue, 27 Jun 2023 10:37:15 -0400 Received: from mail-pl1-x635.google.com (mail-pl1-x635.google.com [IPv6:2607:f8b0:4864:20::635]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 743602D6D; Tue, 27 Jun 2023 07:37:02 -0700 (PDT) Received: by mail-pl1-x635.google.com with SMTP id d9443c01a7336-1b7fb1a82c4so15341895ad.1; Tue, 27 Jun 2023 07:37:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1687876622; x=1690468622; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:from:to :cc:subject:date:message-id:reply-to; bh=g3qBBoPBinM9uTXU87TH/vR1WOzaJAFG3FM+rFMLF54=; b=IPz+v5nf/T0u4wRLY/4MeaZaX+az7xLRtL+fVxrR7eQHSlL/AoasbcdyD7duyR4DAy ELMramw4ZuqUad5pWWnAJRtcKsmKZSvUrA2FKNsMTWwkhEu7K/q23a3FEth9kroV3HsO JbtaGw2KVh1tvB+KIFpngujrKG6/gqXnL4F+4BHJsZCSHgUApJl68+a9rTr5NqO5MDER vqQMfRslhY7j8vXulhrNMpvxHaxN5xi6EbNVEHZ/DM1hcBxrSbr02iCR6GNsY7Fq2INW wcnre2+r49YClpEFBl0lP3fKSnWkIFxgy2lU3hOdGMYr+kqWRAqWVOHl0fSXH2jMiSXd 5VSQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1687876622; x=1690468622; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=g3qBBoPBinM9uTXU87TH/vR1WOzaJAFG3FM+rFMLF54=; b=aj6JDTJkcT0OhJ5/f5IT2crsj7cfk/sn5yVMbWuqolnT58r+LUMmYlxmOrgclKvw71 IxUlTjktNl4exi/6kj6x/2JlIKFXnJZBN9givse0bDDim72qC6Imuq+cPQKLJrezGvlY iWNLS8oF+3yib73+0Ga4+Nd8yLOgIWlF7Z+sse7pAEvApMgW9CIXB6hliUugx8m6xux5 Ndp5V9NjUrjo3MCS9gXkafsHFhCvYi/2i1FrKx0i0F9qPxbkNGbWHicsYhVrkx8xtX6I oxz531SQij9FG7A37YfW4U0AcPLm0zS1DBm+AAw5I8V1+Ek01q8kM/SzamV98+XpcYuL t3hg== X-Gm-Message-State: AC+VfDy7LRinm0ihd7m/gZFJtAVl0MTtf9mL9XHyQDo01ZZcWLwgjeBl XzlsjSQTdZH3qXndIM9FAAdQoHUakuSL5Q== X-Google-Smtp-Source: ACHHUZ6I1MW+JxOBt1ZDqPrCHSMiiDYCa5Ns+cE/SUfVDqyGdhPXGCk9PfsOR1PrbQ4bQAnb1XyA1A== X-Received: by 2002:a17:902:e74c:b0:1b7:d051:89c1 with SMTP id p12-20020a170902e74c00b001b7d05189c1mr8603529plf.53.1687876608872; Tue, 27 Jun 2023 07:36:48 -0700 (PDT) Received: from gmail.com ([2601:600:8500:5f14:d627:c51e:516e:a105]) by smtp.gmail.com with ESMTPSA id s7-20020a170902988700b001ac2be26340sm6115627plp.222.2023.06.27.07.36.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Jun 2023 07:36:48 -0700 (PDT) Date: Tue, 27 Jun 2023 07:36:45 -0700 From: Andrei Vagin To: Muhammad Usama Anjum Cc: =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Peter Xu , David Hildenbrand , Andrew Morton , 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 v21 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs Message-ID: References: <20230626113156.1274521-1-usama.anjum@collabora.com> <20230626113156.1274521-3-usama.anjum@collabora.com> <13ea54c0-25a3-285c-f47e-d6da11c91795@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <13ea54c0-25a3-285c-f47e-d6da11c91795@collabora.com> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Jun 27, 2023 at 02:00:31PM +0500, Muhammad Usama Anjum wrote: > Hi Andrei and Michal, > > Lets resolve last two points. Please reply below. > > On 6/27/23 6:46 AM, Andrei Vagin wrote: > ... > >> +#ifdef CONFIG_HUGETLB_PAGE > >> +static int pagemap_scan_hugetlb_entry(pte_t *ptep, unsigned long hmask, > >> + unsigned long start, unsigned long end, > >> + struct mm_walk *walk) > >> +{ > >> + unsigned long n_pages = (end - start)/PAGE_SIZE; > >> + struct pagemap_scan_private *p = walk->private; > >> + struct vm_area_struct *vma = walk->vma; > >> + bool is_written, is_interesting = true; > >> + struct hstate *h = hstate_vma(vma); > >> + unsigned long bitmap; > >> + spinlock_t *ptl; > >> + int ret = 0; > >> + pte_t ptent; > >> + > >> + if (IS_PM_SCAN_WP(p->flags) && n_pages < HPAGE_SIZE/PAGE_SIZE) > >> + return -EINVAL; > >> + > >> + if (n_pages > p->max_pages - p->found_pages) > >> + n_pages = p->max_pages - p->found_pages; > >> + > >> + if (IS_PM_SCAN_WP(p->flags)) { > >> + i_mmap_lock_write(vma->vm_file->f_mapping); > >> + ptl = huge_pte_lock(h, vma->vm_mm, ptep); > >> + } > >> + > >> + ptent = huge_ptep_get(ptep); > >> + is_written = !is_huge_pte_uffd_wp(ptent); > >> + > >> + /* > >> + * Partial hugetlb page clear isn't supported > >> + */ > >> + if (is_written && IS_PM_SCAN_WP(p->flags) && > >> + n_pages < HPAGE_SIZE/PAGE_SIZE) { > > > > should it be done only if is_interesting is set? > This can be good optimization. We shouldn't return error before finding if > page is interesting. I'll update. > > > > >> + ret = PM_SCAN_END_WALK; > >> + goto unlock_and_return; > >> + } > >> + > >> + bitmap = PM_SCAN_FLAGS(is_written, pagemap_scan_is_huge_file(ptent), > >> + pte_present(ptent), is_swap_pte(ptent), > >> + pte_present(ptent) && is_zero_pfn(pte_pfn(ptent))); > >> + > >> + 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_huge_pte(vma, start, ptep, ptent); > >> + flush_hugetlb_tlb_range(vma, start, end); > >> + } > >> + > >> +unlock_and_return: > >> + if (IS_PM_SCAN_WP(p->flags)) { > >> + spin_unlock(ptl); > >> + i_mmap_unlock_write(vma->vm_file->f_mapping); > >> + } > >> + > >> + return ret; > >> +} > ... > >> + > >> +static long do_pagemap_scan(struct mm_struct *mm, unsigned long __arg) > >> +{ > >> + struct pm_scan_arg __user *uarg = (struct pm_scan_arg __user *)__arg; > >> + unsigned long long start, end, walk_start, walk_end; > >> + unsigned long empty_slots, vec_index = 0; > >> + struct mmu_notifier_range range; > >> + struct page_region __user *vec; > >> + struct pagemap_scan_private p; > >> + struct pm_scan_arg arg; > >> + int ret = 0; > >> + > >> + if (copy_from_user(&arg, uarg, sizeof(arg))) > >> + return -EFAULT; > >> + > >> + start = untagged_addr((unsigned long)arg.start); > >> + vec = (struct page_region *)untagged_addr((unsigned long)arg.vec); > >> + > >> + ret = pagemap_scan_args_valid(&arg, start, vec); > >> + if (ret) > >> + return ret; > >> + > >> + end = start + arg.len; > >> + p.max_pages = (arg.max_pages) ? arg.max_pages : ULONG_MAX; > >> + p.found_pages = 0; > >> + p.required_mask = arg.required_mask; > >> + p.anyof_mask = arg.anyof_mask; > >> + p.excluded_mask = arg.excluded_mask; > >> + p.return_mask = arg.return_mask; > >> + p.flags = arg.flags; > >> + p.flags |= ((p.required_mask | p.anyof_mask | p.excluded_mask) & > >> + PAGE_IS_WRITTEN) ? PM_SCAN_REQUIRE_UFFD : 0; > >> + p.cur_buf.start = p.cur_buf.len = p.cur_buf.flags = 0; > >> + p.vec_buf = NULL; > >> + p.vec_buf_len = PAGEMAP_WALK_SIZE >> PAGE_SHIFT; > >> + > >> + /* > >> + * Allocate smaller buffer to get output from inside the page walk > >> + * functions and walk page range in PAGEMAP_WALK_SIZE size chunks. As > >> + * we want to return output to user in compact form where no two > >> + * consecutive regions should be continuous and have the same flags. > >> + * So store the latest element in p.cur_buf between different walks and > >> + * store the p.cur_buf at the end of the walk to the user buffer. > >> + */ > >> + if (IS_PM_SCAN_GET(p.flags)) { > >> + p.vec_buf = kmalloc_array(p.vec_buf_len, sizeof(*p.vec_buf), > >> + GFP_KERNEL); > >> + if (!p.vec_buf) > >> + return -ENOMEM; > >> + } > >> + > >> + if (IS_PM_SCAN_WP(p.flags)) { > >> + mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0, > >> + mm, start, end); > >> + mmu_notifier_invalidate_range_start(&range); > >> + } > >> + > >> + walk_start = walk_end = start; > >> + while (walk_end < end && !ret) { > >> + if (IS_PM_SCAN_GET(p.flags)) { > >> + p.vec_buf_index = 0; > >> + > >> + /* > >> + * All data is copied to cur_buf first. When more data > >> + * is found, we push cur_buf to vec_buf and copy new > >> + * data to cur_buf. Subtract 1 from length as the > >> + * index of cur_buf isn't counted in length. > >> + */ > >> + empty_slots = arg.vec_len - vec_index; > >> + p.vec_buf_len = min(p.vec_buf_len, empty_slots - 1); > >> + } > >> + > >> + walk_end = (walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK; > >> + if (walk_end > end) > >> + walk_end = end; > >> + > > > > If this loop can run for a long time, we need to interrupt it in case of > > pending signals. > > > > If you think we don't need to do that, pls explain in the commit > > message, so that maintainers don't miss this part and double check that > > everything is alright here. > This can be done. I'll add to the commit message that we are walking over > entire range passed. > > > > >> + ret = mmap_read_lock_killable(mm); > >> + if (ret) > > > > If any pages have been handled, we need to report them to user-space. It > > isn't acceptable to return a error in such cases. > This will return error only when task has gotten some serios signal and it > is giong to be killed. In this scenerio, we shouldn't care about returning > gracefully. Why do you think we should return gracefully in this case? You are right, it can be interrupted only by a fatal signal. You can ignore this comment. > > > > > And we need to report an address where it stopped scanning. > > We can do that by adding zero length vector. > I don't want to do multiplexing the ending address in vec. Can we add > end_addr variable in struct pm_scan_arg to always return the ending address? > > struct pm_scan_arg { > ... > _u64 end_addr; > }; > > > > > > > >> + goto free_data; > >> + ret = walk_page_range(mm, walk_start, walk_end, > >> + &pagemap_scan_ops, &p); > >> + mmap_read_unlock(mm); > >> + > >> + if (ret && ret != PM_SCAN_FOUND_MAX_PAGES && > >> + ret != PM_SCAN_END_WALK) > >> + goto free_data; > >> + > >> + walk_start = walk_end; > >> + if (IS_PM_SCAN_GET(p.flags) && p.vec_buf_index) { > >> + if (copy_to_user(&vec[vec_index], p.vec_buf, > >> + p.vec_buf_index * sizeof(*p.vec_buf))) { > >> + /* > >> + * Return error even though the OP succeeded > >> + */ > >> + ret = -EFAULT; > >> + goto free_data; > >> + } > >> + vec_index += p.vec_buf_index; > > > > Should we set ret to zero here if it is equal PM_SCAN_END_WALK. > No, PM_SCAN_END_WALK is just internal code to stop the page walk and return > immedtitely. When we get this return value, we stop this loop and return to > user with whatever data we have in user buffer. but PM_SCAN_END_WALK is returned when p.vec_buf is full, so we can restart the loop after coping vec_buf to the user buffer, can't we? > > > > >> + } > >> + } > >> + > >> + if (p.cur_buf.len) { > >> + if (copy_to_user(&vec[vec_index], &p.cur_buf, sizeof(p.cur_buf))) { > >> + ret = -EFAULT; > >> + goto free_data; > >> + } > >> + vec_index++; > >> + } > >> + > >> + ret = vec_index; > >> + > >> +free_data: > >> + if (IS_PM_SCAN_WP(p.flags)) > >> + mmu_notifier_invalidate_range_end(&range); > >> + > >> + kfree(p.vec_buf); > >> + return ret; > >> +} > >> + > ... > > -- > BR, > Muhammad Usama Anjum