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@xxxxxxxxxxxxx>
---
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 <linux/shmem_fs.h>
#include <linux/uaccess.h>
#include <linux/pkeys.h>
+#include <linux/minmax.h>
#include <asm/elf.h>
#include <asm/tlb.h>
@@ -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 */
--
2.39.2
