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 usama.anjum@collabora.com --- Changes in v15: - Build fix: - Use generic tlb flush function in pagemap_scan_pmd_entry() instead of using x86 specific flush function in do_pagemap_scan() - Remove #ifdef from pagemap_scan_hugetlb_entry() - Use mm instead of undefined vma->vm_mm
Changes in v14: - Fix build error caused by #ifdef added at last minute in some configs
Changes in v13: - Review updates - mmap_read_lock_killable() instead of mmap_read_lock() - Replace uffd_wp_range() with helpers which increases performance drastically for OP_WP operations by reducing the number of tlb flushing etc - Add MMU_NOTIFY_PROTECTION_VMA notification for the memory range
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
task_mmu
task_mmu
task_mmu.c --- fs/proc/task_mmu.c | 481 ++++++++++++++++++++++++++++++++++++++++ include/uapi/linux/fs.h | 53 +++++ 2 files changed, 534 insertions(+)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 38b19a757281..e119e13a9ba5 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -19,6 +19,7 @@ #include <linux/shmem_fs.h> #include <linux/uaccess.h> #include <linux/pkeys.h> +#include <linux/minmax.h>
#include <asm/elf.h> #include <asm/tlb.h> @@ -1767,11 +1768,491 @@ 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_DO_UFFD_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 is_pte_uffd_wp(pte_t pte) +{ + return (pte_present(pte) && pte_uffd_wp(pte)) || + pte_swp_uffd_wp_any(pte); +} + +static inline void make_uffd_wp_pte(struct vm_area_struct *vma, + unsigned long addr, pte_t *pte) +{ + pte_t ptent = *pte; + + if (pte_present(ptent)) { + pte_t old_pte; + + old_pte = ptep_modify_prot_start(vma, addr, pte); + ptent = pte_mkuffd_wp(ptent); + ptep_modify_prot_commit(vma, addr, pte, old_pte, ptent); + } else if (is_swap_pte(ptent)) { + ptent = pte_swp_mkuffd_wp(ptent); + set_pte_at(vma->vm_mm, addr, pte, ptent); + } +} + +#ifdef CONFIG_TRANSPARENT_HUGEPAGE +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)); +} + +static inline void make_uffd_wp_pmd(struct vm_area_struct *vma, + unsigned long addr, pmd_t *pmdp) +{ + pmd_t old, pmd = *pmdp; + + if (pmd_present(pmd)) { + old = pmdp_invalidate_ad(vma, addr, pmdp); + pmd = pmd_mkuffd_wp(old); + set_pmd_at(vma->vm_mm, addr, pmdp, pmd); + } else if (is_migration_entry(pmd_to_swp_entry(pmd))) { + pmd = pmd_swp_mkuffd_wp(pmd); + set_pmd_at(vma->vm_mm, addr, pmdp, pmd); + } +} +#endif + +#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)); +} + +static inline void make_uffd_wp_huge_pte(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep, + pte_t ptent) +{ + pte_t old_pte; + + if (!huge_pte_none(ptent)) { + old_pte = huge_ptep_modify_prot_start(vma, addr, ptep); + ptent = huge_pte_mkuffd_wp(old_pte); + ptep_modify_prot_commit(vma, addr, ptep, old_pte, ptent); + } else { + set_huge_pte_at(vma->vm_mm, addr, ptep, + make_pte_marker(PTE_MARKER_UFFD_WP)); + } +} +#endif + +static inline bool pagemap_scan_check_page_written(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_check_page_written(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->bitmap == bitmap && + cur->start + cur->len * PAGE_SIZE == addr) { + 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; + } + + /* + * All data is copied to cur first. When more data is found, we push + * cur to vec and copy new data to cur. The vec_index represents the + * current index of vec array. We add 1 to the vec_index while + * performing checks to account for data in cur. + */ + if (p->vec_index && (p->vec_index + 1) >= p->vec_len) + return -ENOSPC; + + if (cur->len) { + memcpy(&p->vec[p->vec_index], cur, sizeof(*p->vec)); + 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; +} + +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; + struct vm_area_struct *vma = walk->vma; + unsigned long addr = end; + pte_t *pte, *orig_pte; + spinlock_t *ptl; + bool is_written; + int ret = 0; + +#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 && PM_SCAN_DO_UFFD_WP(p) && + n_pages < HPAGE_SIZE/PAGE_SIZE) { + spin_unlock(ptl); + split_huge_pmd(vma, pmd, start); + goto process_smaller_pages; + } + + ret = pagemap_scan_output(is_written, vma->vm_file, + pmd_present(*pmd), is_swap_pmd(*pmd), + p, start, n_pages); + + if (ret >= 0 && is_written && PM_SCAN_DO_UFFD_WP(p)) + make_uffd_wp_pmd(vma, addr, pmd); + + spin_unlock(ptl); + + if (PM_SCAN_DO_UFFD_WP(p)) + flush_tlb_range(vma, start, end); + + return ret; + } +process_smaller_pages: + if (pmd_trans_unstable(pmd)) + return 0; +#endif + + orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl); + for (addr = start; addr < end && !ret; pte++, addr += PAGE_SIZE) { + is_written = !is_pte_uffd_wp(*pte); + + ret = pagemap_scan_output(is_written, vma->vm_file, + pte_present(*pte), is_swap_pte(*pte), + p, addr, 1); + + if (ret >= 0 && is_written && PM_SCAN_DO_UFFD_WP(p)) + make_uffd_wp_pte(vma, addr, pte); + } + pte_unmap_unlock(orig_pte, ptl); + + if (PM_SCAN_DO_UFFD_WP(p)) + flush_tlb_range(vma, start, addr); + + 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) +{ + unsigned long n_pages = (end - start)/PAGE_SIZE; + struct pagemap_scan_private *p = walk->private; + struct vm_area_struct *vma = walk->vma; + struct hstate *h = hstate_vma(vma); + int ret = -EPERM; + spinlock_t *ptl; + bool is_written; + pte_t pte; + + if (p->max_pages && n_pages > p->max_pages - p->found_pages) + n_pages = p->max_pages - p->found_pages; + + if (PM_SCAN_DO_UFFD_WP(p)) { + i_mmap_lock_write(vma->vm_file->f_mapping); + ptl = huge_pte_lock(h, vma->vm_mm, ptep); + } + + 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_DO_UFFD_WP(p) && + n_pages < HPAGE_SIZE/PAGE_SIZE) + goto unlock_and_return; + + ret = pagemap_scan_output(is_written, vma->vm_file, pte_present(pte), + is_swap_pte(pte), p, start, n_pages); + if (ret < 0) + goto unlock_and_return; + + if (is_written && PM_SCAN_DO_UFFD_WP(p)) { + make_uffd_wp_huge_pte(vma, start, ptep, pte); + flush_hugetlb_tlb_range(vma, start, end); + } + +unlock_and_return: + if (PM_SCAN_DO_UFFD_WP(p)) { + spin_unlock(ptl); + i_mmap_unlock_write(vma->vm_file->f_mapping); + } + + 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) +{ + unsigned long n_pages = (end - addr)/PAGE_SIZE; + struct pagemap_scan_private *p = walk->private; + struct vm_area_struct *vma = walk->vma; + int ret = 0; + + if (!vma) + return 0; + + 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_DO_UFFD_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_scan(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 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; + 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(*p.vec), GFP_KERNEL); + if (!p.vec) + return -ENOMEM; + + if (p.flags & PM_SCAN_OP_WP) { + 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) { + 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; + + ret = mmap_read_lock_killable(mm); + if (ret) + goto free_data; + 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(*p.vec))) { + /* + * Return error even though the OP succeeded + */ + ret = -EFAULT; + goto free_data; + } + vec_index += p.vec_index; + } + } + + if (p.flags & PM_SCAN_OP_WP) + mmu_notifier_invalidate_range_end(&range); + + if (p.cur.len) { + if (copy_to_user(&vec[vec_index], &p.cur, sizeof(*p.vec))) { + ret = -EFAULT; + goto free_data; + } + vec_index++; + } + + ret = vec_index; + +free_data: + kfree(p.vec); + return ret; +} + +static long do_pagemap_cmd(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_scan(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 = do_pagemap_cmd, + .compat_ioctl = do_pagemap_cmd, }; #endif /* CONFIG_PROC_PAGE_MONITOR */
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 */