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Mon, 03 Jul 2023 08:07:17 -0700 (PDT) Received: from gmail.com ([2601:600:8500:5f14:d627:c51e:516e:a105]) by smtp.gmail.com with ESMTPSA id x2-20020aa79182000000b00682a16f0b00sm273814pfa.210.2023.07.03.08.07.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Jul 2023 08:07:16 -0700 (PDT) Date: Mon, 3 Jul 2023 08:07:14 -0700 From: Andrei Vagin To: Muhammad Usama Anjum Cc: Peter Xu , David Hildenbrand , Andrew Morton , =?utf-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , 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 v22 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs Message-ID: References: <20230628095426.1886064-1-usama.anjum@collabora.com> <20230628095426.1886064-3-usama.anjum@collabora.com> <49015b82-2f7f-fa34-d56a-2f427f38f28f@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <49015b82-2f7f-fa34-d56a-2f427f38f28f@collabora.com> X-Rspamd-Queue-Id: BBCC340027 X-Rspam-User: X-Stat-Signature: xiswrgoja3y5xxi1kcz9wbkynhm686sp X-Rspamd-Server: rspam01 X-HE-Tag: 1688396839-367586 X-HE-Meta: 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 j3SSCFSb 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 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: On Mon, Jul 03, 2023 at 11:47:37AM +0500, Muhammad Usama Anjum wrote: > On 6/30/23 8:01 PM, Andrei Vagin wrote: > > On Wed, Jun 28, 2023 at 02:54:23PM +0500, Muhammad Usama Anjum wrote: > >> This IOCTL, PAGEMAP_SCAN on 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), swapped > >> (PAGE_IS_SWAPPED) or page has pfn zero (PAGE_IS_PFNZERO). > >> - Find pages which have been written-to and/or write protect the pages > >> (atomic PM_SCAN_OP_GET + PM_SCAN_OP_WP) > >> > >> This IOCTL can be extended to get information about more PTE bits. The > >> entire address range passed by user [start, end) is scanned until either > >> the user provided buffer is full or max_pages have been found. > >> > >> Signed-off-by: Muhammad Usama Anjum > > > > > > > >> + > >> +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); > >> + end = untagged_addr((unsigned long)arg.end); > >> + vec = (struct page_region __user *)untagged_addr((unsigned long)arg.vec); > >> + > >> + ret = pagemap_scan_args_valid(&arg, start, end, vec); > >> + if (ret) > >> + return ret; > >> + > >> + 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); > >> + } > >> + > >> + ret = mmap_read_lock_killable(mm); > >> + if (ret) > >> + goto return_status; > >> + > >> + walk_end = min((walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK, end); > >> + > >> + 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 return_status; > >> + > >> + 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 return_status; > >> + } > >> + vec_index += p.vec_buf_index; > >> + } > >> + } > >> + > >> + if (p.cur_buf.len) { > >> + if (copy_to_user(&vec[vec_index], &p.cur_buf, sizeof(p.cur_buf))) { > >> + ret = -EFAULT; > >> + goto return_status; > >> + } > >> + vec_index++; > >> + } > >> + > >> + ret = vec_index; > >> + > >> +return_status: > >> + arg.start = (unsigned long)walk_end; > > > > This doesn't look right. pagemap_scan_pmd_entry can stop early. For > > example, it can happen when it hits the max_pages limit. Do I miss > > something? > The walk_page_range() calls pagemap_scan_pmd_entry(). So whatever status is > returned from pagemap_scan_pmd_entry(), walk_page_range() returns to this > function where we are handling the status code. After while loop starts, > there is only 1 return path. Hence there isn't any path missing where we'll > miss setting arg.start. I mean walk_end isn't actually the end address. The end adress should be the next page after the last revised page. Here we don't know whether all pages in [walk_start, walk_end) has been revised. > > > > >> + if (copy_to_user(&uarg->start, &arg.start, sizeof(arg.start))) > >> + ret = -EFAULT; > >> + > >> + if (IS_PM_SCAN_WP(p.flags)) > >> + mmu_notifier_invalidate_range_end(&range); > >> + > >> + kfree(p.vec_buf); > >> + return ret; > >> +} > >> + > > -- > BR, > Muhammad Usama Anjum