From patchwork Thu Apr 6 07:40:02 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Muhammad Usama Anjum X-Patchwork-Id: 670918 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 8066EC76196 for ; Thu, 6 Apr 2023 07:41:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235995AbjDFHlB (ORCPT ); Thu, 6 Apr 2023 03:41:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51710 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235863AbjDFHkt (ORCPT ); Thu, 6 Apr 2023 03:40:49 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D64C97DB6; Thu, 6 Apr 2023 00:40:45 -0700 (PDT) Received: from localhost.localdomain (unknown [119.155.57.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: usama.anjum) by madras.collabora.co.uk (Postfix) with ESMTPSA id 5E55366031C9; Thu, 6 Apr 2023 08:40:37 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1680766844; bh=J4il6WS3cHY4Rx9kmofpVaVxCFP1F2wXdnJaquJwTds=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=oqf32i45qL66RfZQOlMOd15/XRgyMoDvP4y683f8Q4PNlbkbMNW1kQ5LGHKffjQoH WafrhiVFiyLPFlerG8fvI5DufgNHQREdvVfSsfEziW+2zrvjV9WlRLS9voVBl8ikWa xH1m0Rnyakrs9giCP0BFyfq/SquzFYRbOg+oyBm7PgsvzTXnEGthCdy4DykjJ/eX2d IB6kVfZF6OnN6umJtzu1w7B+qPOwaaA1gB6StNeCRlHZM5WVSLBmCjmdS2BG/Hy/bU 3C4DPj7Ioiuh28mZoi/YNT+AUlclwdAMpa/jM1qp6Cs0Ee5/S1gHtoElkYvWbQIUyd JaRqAKAJvlv5g== From: Muhammad Usama Anjum To: Peter Xu , David Hildenbrand , Andrew Morton , =?utf-8?b?TWljaGHFgiBNaXJvc8WC?= =?utf-8?b?YXc=?= , Andrei Vagin , Danylo Mocherniuk , Paul Gofman , Cyrill Gorcunov , Mike Rapoport , Nadav Amit Cc: Alexander Viro , Shuah Khan , Christian Brauner , Yang Shi , Vlastimil Babka , "Liam R . Howlett" , Yun Zhou , Suren Baghdasaryan , Alex Sierra , Muhammad Usama Anjum , 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: [PATCH v12 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs Date: Thu, 6 Apr 2023 12:40:02 +0500 Message-Id: <20230406074005.1784728-3-usama.anjum@collabora.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230406074005.1784728-1-usama.anjum@collabora.com> References: <20230406074005.1784728-1-usama.anjum@collabora.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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) or swapped (PAGE_IS_SWAPPED). - Find pages which have been written-to and write protect the pages (atomic PAGE_IS_WRITTEN + PAGEMAP_WP_ENGAGE) This IOCTL can be extended to get information about more PTE bits. Signed-off-by: Muhammad Usama Anjum --- Changes in v12: - Add hugetlb support to cover all memory types - Merge "userfaultfd: Define dummy uffd_wp_range()" with this patch - Review updates to the code Changes in v11: - Find written pages in a better way - Fix a corner case (thanks Paul) - Improve the code/comments - remove ENGAGE_WP + ! GET operation - shorten the commit message in favour of moving documentation to pagemap.rst Changes in v10: - move changes in tools/include/uapi/linux/fs.h to separate patch - update commit message Change in v8: - Correct is_pte_uffd_wp() - Improve readability and error checks - Remove some un-needed code Changes in v7: - Rebase on top of latest next - Fix some corner cases - Base soft-dirty on the uffd wp async - Update the terminologies - Optimize the memory usage inside the ioctl Changes in v6: - Rename variables and update comments - Make IOCTL independent of soft_dirty config - Change masks and bitmap type to _u64 - Improve code quality Changes in v5: - Remove tlb flushing even for clear operation Changes in v4: - Update the interface and implementation Changes in v3: - Tighten the user-kernel interface by using explicit types and add more error checking Changes in v2: - Convert the interface from syscall to ioctl - Remove pidfd support as it doesn't make sense in ioctl --- fs/proc/task_mmu.c | 426 ++++++++++++++++++++++++++++++++++ include/linux/userfaultfd_k.h | 8 + include/uapi/linux/fs.h | 53 +++++ 3 files changed, 487 insertions(+) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 6134f0df4164..36531b04bcd6 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -19,6 +19,7 @@ #include #include #include +#include #include #include @@ -1135,6 +1136,26 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma, } #endif +static inline bool is_pte_uffd_wp(pte_t pte) +{ + return ((pte_present(pte) && pte_uffd_wp(pte)) || + pte_swp_uffd_wp_any(pte)); +} + +#ifdef CONFIG_HUGETLB_PAGE +static inline bool is_huge_pte_uffd_wp(pte_t pte) +{ + return ((pte_present(pte) && huge_pte_uffd_wp(pte)) || + pte_swp_uffd_wp_any(pte)); +} +#endif + +static inline bool is_pmd_uffd_wp(pmd_t pmd) +{ + return ((pmd_present(pmd) && pmd_uffd_wp(pmd)) || + (is_swap_pmd(pmd) && pmd_swp_uffd_wp(pmd))); +} + #if defined(CONFIG_MEM_SOFT_DIRTY) && defined(CONFIG_TRANSPARENT_HUGEPAGE) static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmdp) @@ -1768,11 +1789,416 @@ static int pagemap_release(struct inode *inode, struct file *file) return 0; } +#define PM_SCAN_FOUND_MAX_PAGES (1) +#define PM_SCAN_BITS_ALL (PAGE_IS_WRITTEN | PAGE_IS_FILE | \ + PAGE_IS_PRESENT | PAGE_IS_SWAPPED) +#define PM_SCAN_OPS (PM_SCAN_OP_GET | PM_SCAN_OP_WP) +#define PM_SCAN_OP_IS_WP(a) (a->flags & PM_SCAN_OP_WP) +#define PM_SCAN_BITMAP(wt, file, present, swap) \ + (wt | file << 1 | present << 2 | swap << 3) + +struct pagemap_scan_private { + struct page_region *vec; + struct page_region cur; + unsigned long vec_len, vec_index; + unsigned int max_pages, found_pages, flags; + unsigned long required_mask, anyof_mask, excluded_mask, return_mask; +}; + +static inline bool pagemap_scan_is_written_set(struct pagemap_scan_private *p) +{ + return ((p->required_mask | p->anyof_mask | p->excluded_mask) & + PAGE_IS_WRITTEN); +} + +static int pagemap_scan_test_walk(unsigned long start, unsigned long end, + struct mm_walk *walk) +{ + struct pagemap_scan_private *p = walk->private; + struct vm_area_struct *vma = walk->vma; + + if (pagemap_scan_is_written_set(p) && (!userfaultfd_wp(vma) || + !userfaultfd_wp_async(vma))) + return -EPERM; + + if (vma->vm_flags & VM_PFNMAP) + return 1; + + return 0; +} + +static int pagemap_scan_output(bool wt, bool file, bool pres, bool swap, + struct pagemap_scan_private *p, + unsigned long addr, unsigned int n_pages) +{ + unsigned long bitmap = PM_SCAN_BITMAP(wt, file, pres, swap); + struct page_region *cur = &p->cur; + + if (!n_pages) + return -EINVAL; + + if ((p->required_mask & bitmap) != p->required_mask) + return 0; + if (p->anyof_mask && !(p->anyof_mask & bitmap)) + return 0; + if (p->excluded_mask & bitmap) + return 0; + + bitmap &= p->return_mask; + if (!bitmap) + return 0; + + if ((cur->start + cur->len * PAGE_SIZE == addr) && + (cur->bitmap == bitmap)) { + cur->len += n_pages; + p->found_pages += n_pages; + + if (p->max_pages && (p->found_pages == p->max_pages)) + return PM_SCAN_FOUND_MAX_PAGES; + + return 0; + } + + if (!p->vec_index || ((p->vec_index + 1) < p->vec_len)) { + + if (cur->len) { + memcpy(&p->vec[p->vec_index], cur, + sizeof(struct page_region)); + p->vec_index++; + } + cur->start = addr; + cur->len = n_pages; + cur->bitmap = bitmap; + p->found_pages += n_pages; + + if (p->max_pages && (p->found_pages == p->max_pages)) + return PM_SCAN_FOUND_MAX_PAGES; + + return 0; + } + + return -ENOSPC; +} + +static inline int pagemap_scan_deposit(struct pagemap_scan_private *p, + struct page_region __user *vec, + unsigned long *vec_index) +{ + struct page_region *cur = &p->cur; + + if (!cur->len) + return 0; + + if (copy_to_user(&vec[*vec_index], cur, sizeof(struct page_region))) + return -EFAULT; + + p->vec_index++; + (*vec_index)++; + + return 0; +} + +static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start, + unsigned long end, struct mm_walk *walk) +{ + struct pagemap_scan_private *p = walk->private; + bool is_written, is_file, is_present, is_swap; + struct vm_area_struct *vma = walk->vma; + unsigned long addr = end; + spinlock_t *ptl; + int ret = 0; + pte_t *pte; + +#ifdef CONFIG_TRANSPARENT_HUGEPAGE + ptl = pmd_trans_huge_lock(pmd, vma); + if (ptl) { + unsigned long n_pages = (end - start)/PAGE_SIZE; + + is_written = !is_pmd_uffd_wp(*pmd); + is_file = vma->vm_file; + is_present = pmd_present(*pmd); + is_swap = is_swap_pmd(*pmd); + + spin_unlock(ptl); + + /* + * Break huge page into small pages if the WP operation need to + * be performed is on a portion of the huge page or if max_pages + * pages limit would exceed. + */ + if (is_written && PM_SCAN_OP_IS_WP(p) && + ((end - start < HPAGE_SIZE) || + (p->max_pages && + (p->max_pages - p->found_pages) < n_pages))) { + + split_huge_pmd(vma, pmd, start); + goto process_smaller_pages; + } + + if (p->max_pages && + p->found_pages + n_pages > p->max_pages) + n_pages = p->max_pages - p->found_pages; + + ret = pagemap_scan_output(is_written, is_file, is_present, + is_swap, p, start, n_pages); + if (ret < 0) + return ret; + + if (is_written && PM_SCAN_OP_IS_WP(p) && + uffd_wp_range(vma, start, HPAGE_SIZE, true) < 0) + ret = -EINVAL; + + return ret; + } +process_smaller_pages: + if (pmd_trans_unstable(pmd)) + return 0; +#endif + + for (addr = start; addr < end && !ret; pte++, addr += PAGE_SIZE) { + pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); + + is_written = !is_pte_uffd_wp(*pte); + is_file = vma->vm_file; + is_present = pte_present(*pte); + is_swap = is_swap_pte(*pte); + + pte_unmap_unlock(pte, ptl); + + ret = pagemap_scan_output(is_written, is_file, is_present, + is_swap, p, addr, 1); + if (ret < 0) + return ret; + + if (is_written && PM_SCAN_OP_IS_WP(p) && + uffd_wp_range(vma, addr, PAGE_SIZE, true) < 0) + return -EINVAL; + } + + cond_resched(); + return ret; +} + +#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) +{ + struct pagemap_scan_private *p = walk->private; + bool is_written; + struct vm_area_struct *vma = walk->vma; + unsigned long n_pages = (end - start)/PAGE_SIZE; + pte_t pte; + int ret; + + pte = huge_ptep_get(ptep); + is_written = !is_huge_pte_uffd_wp(pte); + + /* + * Partial hugetlb page clear isn't supported + */ + if (is_written && PM_SCAN_OP_IS_WP(p) && + ((end - start < HPAGE_SIZE) || + (p->max_pages && + (p->max_pages - p->found_pages) < n_pages))) + return -EPERM; + + if (p->max_pages && + p->found_pages + n_pages > p->max_pages) + n_pages = p->max_pages - p->found_pages; + + ret = pagemap_scan_output(is_written, vma->vm_file, pte_present(pte), + is_swap_pte(pte), p, start, n_pages); + if (ret < 0) + return ret; + + if (is_written && PM_SCAN_OP_IS_WP(p) && + uffd_wp_range(vma, start, HPAGE_SIZE, true) < 0) + ret = -EINVAL; + + return ret; +} +#else +#define pagemap_scan_hugetlb_entry NULL +#endif + +static int pagemap_scan_pte_hole(unsigned long addr, unsigned long end, + int depth, struct mm_walk *walk) +{ + struct pagemap_scan_private *p = walk->private; + struct vm_area_struct *vma = walk->vma; + unsigned long n_pages; + int ret = 0; + + if (!vma) + return 0; + + n_pages = (end - addr)/PAGE_SIZE; + if (p->max_pages && p->found_pages + n_pages > p->max_pages) + n_pages = p->max_pages - p->found_pages; + + ret = pagemap_scan_output(false, vma->vm_file, false, false, p, addr, + n_pages); + + return ret; +} + +static const struct mm_walk_ops pagemap_scan_ops = { + .test_walk = pagemap_scan_test_walk, + .pmd_entry = pagemap_scan_pmd_entry, + .pte_hole = pagemap_scan_pte_hole, + .hugetlb_entry = pagemap_scan_hugetlb_entry, +}; + +static int pagemap_scan_args_valid(struct pm_scan_arg *arg, unsigned long start, + struct page_region __user *vec) +{ + /* Detect illegal size, flags, len and masks */ + if (arg->size != sizeof(struct pm_scan_arg)) + return -EINVAL; + if (arg->flags & ~PM_SCAN_OPS) + return -EINVAL; + if (!arg->len) + return -EINVAL; + if ((arg->required_mask | arg->anyof_mask | arg->excluded_mask | + arg->return_mask) & ~PM_SCAN_BITS_ALL) + return -EINVAL; + if (!arg->required_mask && !arg->anyof_mask && + !arg->excluded_mask) + return -EINVAL; + if (!arg->return_mask) + return -EINVAL; + + /* Validate memory ranges */ + if (!(arg->flags & PM_SCAN_OP_GET)) + return -EINVAL; + if (!arg->vec) + return -EINVAL; + if (arg->vec_len == 0) + return -EINVAL; + + if (!IS_ALIGNED(start, PAGE_SIZE)) + return -EINVAL; + if (!access_ok((void __user *)start, arg->len)) + return -EFAULT; + + if (!PM_SCAN_OP_IS_WP(arg)) + return 0; + + if ((arg->required_mask | arg->anyof_mask | arg->excluded_mask) & + ~PAGE_IS_WRITTEN) + return -EINVAL; + + return 0; +} + +static long do_pagemap_cmd(struct mm_struct *mm, + struct pm_scan_arg __user *uarg) +{ + unsigned long start, end, walk_start, walk_end; + unsigned long empty_slots, vec_index = 0; + 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 = (unsigned long)untagged_addr(arg.start); + vec = (struct page_region *)(unsigned long)untagged_addr(arg.vec); + + ret = pagemap_scan_args_valid(&arg, start, vec); + if (ret) + return ret; + + end = start + arg.len; + p.max_pages = arg.max_pages; + p.found_pages = 0; + p.flags = arg.flags; + 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.cur.len = 0; + p.cur.start = 0; + p.vec = NULL; + p.vec_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 between different walks and + * store the p.cur at the end of the walk to the user buffer. + */ + p.vec = kmalloc_array(p.vec_len, sizeof(struct page_region), + GFP_KERNEL); + if (!p.vec) + return -ENOMEM; + + walk_start = walk_end = start; + while (walk_end < end && !ret) { + p.vec_index = 0; + + empty_slots = arg.vec_len - vec_index; + p.vec_len = min(p.vec_len, empty_slots); + + walk_end = (walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK; + if (walk_end > end) + walk_end = end; + + mmap_read_lock(mm); + ret = walk_page_range(mm, walk_start, walk_end, + &pagemap_scan_ops, &p); + mmap_read_unlock(mm); + + if (ret && ret != -ENOSPC && ret != PM_SCAN_FOUND_MAX_PAGES) + goto free_data; + + walk_start = walk_end; + if (p.vec_index) { + if (copy_to_user(&vec[vec_index], p.vec, + p.vec_index * + sizeof(struct page_region))) { + ret = -EFAULT; + goto free_data; + } + vec_index += p.vec_index; + } + } + ret = pagemap_scan_deposit(&p, vec, &vec_index); + if (!ret) + ret = vec_index; +free_data: + kfree(p.vec); + + return ret; +} + +static long pagemap_scan_ioctl(struct file *file, unsigned int cmd, + unsigned long arg) +{ + struct pm_scan_arg __user *uarg = (struct pm_scan_arg __user *)arg; + struct mm_struct *mm = file->private_data; + + switch (cmd) { + case PAGEMAP_SCAN: + return do_pagemap_cmd(mm, uarg); + + default: + return -EINVAL; + } +} + const struct file_operations proc_pagemap_operations = { .llseek = mem_lseek, /* borrow this */ .read = pagemap_read, .open = pagemap_open, .release = pagemap_release, + .unlocked_ioctl = pagemap_scan_ioctl, + .compat_ioctl = pagemap_scan_ioctl, }; #endif /* CONFIG_PROC_PAGE_MONITOR */ diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index ce4f9d18de3e..325672cd6d6f 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -210,6 +210,14 @@ extern bool userfaultfd_wp_async(struct vm_area_struct *vma); #else /* CONFIG_USERFAULTFD */ +static inline long uffd_wp_range(struct mm_struct *dst_mm, + struct vm_area_struct *vma, + unsigned long start, unsigned long len, + bool enable_wp) +{ + return 0; +} + /* mm helpers */ static inline vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index b7b56871029c..47879c38ce2f 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -305,4 +305,57 @@ typedef int __bitwise __kernel_rwf_t; #define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\ RWF_APPEND) +/* Pagemap ioctl */ +#define PAGEMAP_SCAN _IOWR('f', 16, struct pm_scan_arg) + +/* Bits are set in the bitmap of the page_region and masks in pm_scan_args */ +#define PAGE_IS_WRITTEN (1 << 0) +#define PAGE_IS_FILE (1 << 1) +#define PAGE_IS_PRESENT (1 << 2) +#define PAGE_IS_SWAPPED (1 << 3) + +/* + * struct page_region - Page region with bitmap flags + * @start: Start of the region + * @len: Length of the region in pages + * bitmap: Bits sets for the region + */ +struct page_region { + __u64 start; + __u64 len; + __u64 bitmap; +}; + +/* + * struct pm_scan_arg - Pagemap ioctl argument + * @size: Size of the structure + * @flags: Flags for the IOCTL + * @start: Starting address of the region + * @len: Length of the region (All the pages in this length are included) + * @vec: Address of page_region struct array for output + * @vec_len: Length of the page_region struct array + * @max_pages: Optional max return pages + * @required_mask: Required mask - All of these bits have to be set in the PTE + * @anyof_mask: Any mask - Any of these bits are set in the PTE + * @excluded_mask: Exclude mask - None of these bits are set in the PTE + * @return_mask: Bits that are to be reported in page_region + */ +struct pm_scan_arg { + __u64 size; + __u64 flags; + __u64 start; + __u64 len; + __u64 vec; + __u64 vec_len; + __u64 max_pages; + __u64 required_mask; + __u64 anyof_mask; + __u64 excluded_mask; + __u64 return_mask; +}; + +/* Supported flags */ +#define PM_SCAN_OP_GET (1 << 0) +#define PM_SCAN_OP_WP (1 << 1) + #endif /* _UAPI_LINUX_FS_H */ From patchwork Thu Apr 6 07:40:04 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Muhammad Usama Anjum X-Patchwork-Id: 670917 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 200C6C7618D for ; Thu, 6 Apr 2023 07:41:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235677AbjDFHla (ORCPT ); Thu, 6 Apr 2023 03:41:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51992 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235248AbjDFHlO (ORCPT ); Thu, 6 Apr 2023 03:41:14 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 53F297EF1; Thu, 6 Apr 2023 00:41:00 -0700 (PDT) Received: from localhost.localdomain (unknown [119.155.57.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: usama.anjum) by madras.collabora.co.uk (Postfix) with ESMTPSA id 9B3FE66031CB; Thu, 6 Apr 2023 08:40:52 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1680766859; bh=VHJ3s/rDqou65z21qPz74d3WACjlrCHoe/eBuZI6JGE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MvBethjnSqLziHDGb5lsW7clVQOn8ym6wN8Ykia5gTWmyLYjUxnGEQsodqcFWL+nL LT/acVr12kRkaX71ZZ2vhqMX2beAZulOESNLUtvhn0CZzHjw1DkqW7p6n/t0+Bl2uf bezEYGX8mqyIlWZmmcaNWfSsJvIkuifCtL49PqGSt49Eh83d1uRgdXKa1rYLXt9uvG ZkvdolZMQmk6+8z74c7noGTFGgm8Ma/BGHU0u80QEm1DWav0PicHznNY3CFbtPq/nB vfCB9gwtk3JjcLNvOYSgG4bX1FQmzr+GP2o4cAk8Lobsk39kBT0Z0vIEWmgahGaxXP oiCE19+8VKvCg== From: Muhammad Usama Anjum To: Peter Xu , David Hildenbrand , Andrew Morton , =?utf-8?b?TWljaGHFgiBNaXJvc8WC?= =?utf-8?b?YXc=?= , Andrei Vagin , Danylo Mocherniuk , Paul Gofman , Cyrill Gorcunov , Mike Rapoport , Nadav Amit Cc: Alexander Viro , Shuah Khan , Christian Brauner , Yang Shi , Vlastimil Babka , "Liam R . Howlett" , Yun Zhou , Suren Baghdasaryan , Alex Sierra , Muhammad Usama Anjum , 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: [PATCH v12 4/5] mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL Date: Thu, 6 Apr 2023 12:40:04 +0500 Message-Id: <20230406074005.1784728-5-usama.anjum@collabora.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230406074005.1784728-1-usama.anjum@collabora.com> References: <20230406074005.1784728-1-usama.anjum@collabora.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Add some explanation and method to use write-protection and written-to on memory range. Signed-off-by: Muhammad Usama Anjum --- Changes in v11: - Add more documentation --- Documentation/admin-guide/mm/pagemap.rst | 56 ++++++++++++++++++++++++ 1 file changed, 56 insertions(+) diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst index c8f380271cad..a3e08f15b433 100644 --- a/Documentation/admin-guide/mm/pagemap.rst +++ b/Documentation/admin-guide/mm/pagemap.rst @@ -227,3 +227,59 @@ Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is always 12 at most architectures). Since Linux 3.11 their meaning changes after first clear of soft-dirty bits. Since Linux 4.2 they are used for flags unconditionally. + +Pagemap Scan IOCTL +================== + +The ``PAGEMAP_SCAN`` IOCTL on the pagemap file can be used to get or optionally +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``) or swapped + (``PAGE_IS_SWAPPED``). +- Find pages which have been written-to and write protect the pages atomically + (atomic ``PAGE_IS_WRITTEN + PAGEMAP_WP_ENGAGE``) + +The ``struct pm_scan_arg`` is used as the argument of the IOCTL. + 1. The size of the ``struct pm_scan_arg`` must be specified in the ``size`` + field. This field will be helpful in recognizing the structure if extensions + are done later. + 2. The flags can be specified in the ``flags`` field. The ``PM_SCAN_OP_GET`` + and ``PM_SCAN_OP_WP`` are the only added flag at this time. + 3. The range is specified through ``start`` and ``len``. + 4. The output buffer of ``struct page_region`` array and size is specified in + ``vec`` and ``vec_len``. + 5. The optional maximum requested pages are specified in the ``max_pages``. + 6. The masks are specified in ``required_mask``, ``anyof_mask``, + ``excluded_ mask`` and ``return_mask``. + 1. To find if ``PAGE_IS_WRITTEN`` flag is set for pages which have + ``PAGE_IS_FILE`` set and ``PAGE_IS_SWAPPED`` un-set, ``required_mask`` + is set to ``PAGE_IS_FILE``, ``exclude_mask`` is set to + ``PAGE_IS_SWAPPED`` and ``return_mask`` is set to ``PAGE_IS_WRITTEN``. + The output buffer in ``vec`` and length must be specified in ``vec_len``. + 2. To find pages which have either ``PAGE_IS_FILE`` or ``PAGE_IS_SWAPPED`` + set, ``anyof_masks`` is set to ``PAGE_IS_FILE | PAGE_IS_SWAPPED``. + 3. To find written pages and engage write protect, ``PAGE_IS_WRITTEN`` is + specified in ``required_mask`` and ``return_mask``. In addition to + specifying the output buffer in ``vec`` and length in ``vec_len``, the + ``PAGEMAP_WP_ENGAGE`` is specified in ``flags`` to perform write protect + on the range as well. + +The ``PAGE_IS_WRITTEN`` flag can be considered as the better and correct +alternative of soft-dirty flag. It doesn't get affected by household chores (VMA +merging) of the kernel and hence the user can find the true soft-dirty pages +only. This IOCTL adds the atomic way to find which pages have been written and +write protect those pages again. This kind of operation is needed to efficiently +find out which pages have changed in the memory. + +To get information about which pages have been written-to or optionally write +protect the pages, following must be performed first in order: + 1. The userfaultfd file descriptor is created with ``userfaultfd`` syscall. + 2. The ``UFFD_FEATURE_WP_UNPOPULATED`` and ``UFFD_FEATURE_WP_ASYNC`` features + are set by ``UFFDIO_API`` IOCTL. + 3. The memory range is registered with ``UFFDIO_REGISTER_MODE_WP`` mode + through ``UFFDIO_REGISTER`` IOCTL. + 4. Then the any part of the registered memory or the whole memory region must + be write protected using the ``UFFDIO_WRITEPROTECT`` IOCTL. + 5. Now the ``PAGEMAP_SCAN`` IOCTL can be used to either just find pages which + have been written-to or optionally write protect the pages as well.