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Fri, 30 Jun 2023 08:01:16 -0700 (PDT) Date: Fri, 30 Jun 2023 08:01:14 -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> MIME-Version: 1.0 Content-Type: text/plain; charset=koi8-r Content-Disposition: inline In-Reply-To: <20230628095426.1886064-3-usama.anjum@collabora.com> X-Rspamd-Queue-Id: 143B11400BA X-Rspam-User: X-Stat-Signature: n33t4mhunx53t1ary3so1uhk5oysxs5r X-Rspamd-Server: rspam03 X-HE-Tag: 1688137279-117718 X-HE-Meta: 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 jysK2fLh sFT8edWInUi6GDgWCBBC8otnUO8PqerbwzAfvaMBa+4J1fd1QGx7q3uN/xYmHLeC9NXLPdBL77Q4dNqOpd6V82NH0rRsSm10P9v4Fy33/IoStKN4LUsfYf8G0dkacFpKBr8D17S4/Lyr2q9ZRfU6nTG+dMw8tUfb5kP+s1xgy1xFtJ8H0x2AdmXJ+pSrjIjtLvWFS9rLTd0T6HNfEDCbEYq8vfb7kLHRsa74hTesLrVFBgRGhS8I+CY4xqPDn6vbgLGBZlgdBu0GU1eaNrJ81/ZP4eh8EPlW0EoqiT9/Li5j7M+OfSgMj3ke9+AVAMJTKxPA3Ia4DadSFkw8sw6vTW+VGM1BkXfT6BnMYWljcDfSAs7a0j3rqEk+3xYhLnZN3hMWwUAkcYzIl1VqjZ3j0u7T+5JoVNENZ43e8VFz+PGppBf03eetGcXRlR3NsaQEhcmc/qGJfpmLxGEuFZhhrkI3haQD83hKKNoTncllZWJ9fOJ46GML7tC7dKa6yhYpKOkWWeCiC/fbUXZTCcT1vlzoP60aGDyMUr7wEkYGwRutWky6/v/ULgx89ZJ7nlB4B5A9V 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 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? > + 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; > +} > +