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Fri, 16 Jun 2023 23:39:25 -0700 (PDT) Date: Fri, 16 Jun 2023 23:39:22 -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 v19 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs Message-ID: References: <20230615141144.665148-1-usama.anjum@collabora.com> <20230615141144.665148-3-usama.anjum@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=koi8-r Content-Disposition: inline In-Reply-To: <20230615141144.665148-3-usama.anjum@collabora.com> X-Rspamd-Queue-Id: 50792180014 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: oskq83gnyopp36r16hryzepetn1nce5c X-HE-Tag: 1686983967-884502 X-HE-Meta: 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 Zrksoo36 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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 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); > + 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 was trying to integrate this new interace into CRIU and I found one more thing that is required. We need to detect zero pages. 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))); Thanks, Andrei