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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> X-Rspam-User: X-Stat-Signature: yfs6anwxsqae8gedjcssg7irr46we4ek X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: D29F0C000D X-HE-Tag: 1687876622-602535 X-HE-Meta: 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 GxGjnJJw UBRzUFXIWjgllle7s6de15kCX1U024ZQuXkqiUBFc5pOR0DNhcDhyM9ygsB8Tr55NC1fyVGw2ibl6vgqgRPw0aunfeFg66O3KT75/733wX/dtTn4R1VqUfqQ5GsS8ihJAHhwTtlzmKNhWPMLY8MhN3ryvYjPsfvDQe9Oz8/fLqnM1smjoIbvqJCl1woKUh3Ridz3gC5EVHQHG4TrWD/rufeEWla5D5roeXTpgOSm4My55VB01C9OzKLZ9V+q2Bc1yOmdTb+UcC9afei0sR0sxeQID7SbhTlFbrh3/jOutSmJRzfYc6iGdwKf+DxOnAaRL4fxpYiX+t9Mi46ZxlqQwT4clirWlLG16ukcIuOUOngQg3gopUawZgO/7i0EiyutVZtR/xygpSban5JLRoRtNVNs3RwjOIq46+yyF4UxpyIXVaLUxkI0+J4duwSHXHq9BOKE8hur/HwnsahK5gjV4t5ECnGY9ynPdQVpgO+RIZkFUBMw= 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 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