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_Wt),
file mapped (PAGE_IS_FILE), present (PAGE_IS_PRESENT) or swapped
(PAGE_IS_SWAPPED).
- Write-protect the pages (PAGEMAP_WP_ENGAGE) to start finding which
pages have been written-to.
- Find pages which have been written-to and write protect the pages
(atomic PAGE_IS_NOT_WP + PAGEMAP_WP_ENGAGE)
The uffd should have been registered on the memory range before performing
any WP/WT (Write Protect/Writtern-To) related operations with the IOCTL.
struct pagemap_scan_args is used as the argument of the IOCTL. In this
struct:
- The range is specified through start and len.
- The output buffer and size is specified as vec and vec_len.
- The optional maximum requested pages are specified in the max_pages.
- The flags can be specified in the flags field. The PAGEMAP_WP_ENGAGE
is the only added flag at this time.
- The masks are specified in required_mask, anyof_mask, excluded_ mask
and return_mask.
This IOCTL can be extended to get information about more PTE bits. This
patch has evolved from a basic patch from Gabriel Krisman Bertazi.
Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
---
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 | 300 ++++++++++++++++++++++++++++++++++
include/uapi/linux/fs.h | 50 ++++++
tools/include/uapi/linux/fs.h | 50 ++++++
3 files changed, 400 insertions(+)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index e35a0398db63..ba70faadf403 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 +1136,22 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma,
}
#endif
+static inline bool is_pte_uffd_wp(pte_t pte)
+{
+ if ((pte_present(pte) && pte_uffd_wp(pte)) ||
+ (is_swap_pte(pte) && pte_swp_uffd_wp(pte)))
+ return true;
+ return false;
+}
+
+static inline bool is_pmd_uffd_wp(pmd_t pmd)
+{
+ if ((pmd_present(pmd) && pmd_uffd_wp(pmd)) ||
+ (is_swap_pmd(pmd) && pmd_swp_uffd_wp(pmd)))
+ return true;
+ return false;
+}
+
#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)
@@ -1763,11 +1780,294 @@ static int pagemap_release(struct inode *inode, struct file *file)
return 0;
}
+#define PAGEMAP_OP_MASK (PAGE_IS_WT | PAGE_IS_FILE | \
+ PAGE_IS_PRESENT | PAGE_IS_SWAPPED)
+#define PAGEMAP_NONWT_OP_MASK (PAGE_IS_FILE | PAGE_IS_PRESENT | PAGE_IS_SWAPPED)
+#define IS_WP_ENGAGE_OP(a) (a->flags & PAGEMAP_WP_ENGAGE)
+#define IS_GET_OP(a) (a->vec)
+#define PAGEMAP_SCAN_BITMAP(wt, file, present, swap) \
+ (wt | file << 1 | present << 2 | swap << 3)
+#define IS_WT_REQUIRED(a) \
+ ((a->required_mask & PAGE_IS_WT) || \
+ (a->anyof_mask & PAGE_IS_WT))
+
+struct pagemap_scan_private {
+ struct page_region *vec;
+ struct page_region prev;
+ unsigned long vec_len, vec_index;
+ unsigned int max_pages, found_pages, flags;
+ unsigned long required_mask, anyof_mask, excluded_mask, return_mask;
+};
+
+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 (IS_WT_REQUIRED(p) && !vma_can_userfault(vma, vma->vm_flags))
+ return -EPERM;
+ if (IS_GET_OP(p) && p->max_pages && (p->found_pages == p->max_pages))
+ return -ENOSPC;
+ if (vma->vm_flags & VM_PFNMAP)
+ return 1;
+ return 0;
+}
+
+static inline int add_to_out(bool wt, bool file, bool pres, bool swap,
+ struct pagemap_scan_private *p, unsigned long addr, unsigned int len)
+{
+ unsigned long bitmap, cur = PAGEMAP_SCAN_BITMAP(wt, file, pres, swap);
+ bool cpy = true;
+ struct page_region *prev = &p->prev;
+
+ if (p->required_mask)
+ cpy = ((p->required_mask & cur) == p->required_mask);
+ if (cpy && p->anyof_mask)
+ cpy = (p->anyof_mask & cur);
+ if (cpy && p->excluded_mask)
+ cpy = !(p->excluded_mask & cur);
+ bitmap = cur & p->return_mask;
+ if (cpy && bitmap) {
+ if ((prev->len) && (prev->bitmap == bitmap) &&
+ (prev->start + prev->len * PAGE_SIZE == addr)) {
+ prev->len += len;
+ p->found_pages += len;
+ } else if (p->vec_index < p->vec_len) {
+ if (prev->len) {
+ memcpy(&p->vec[p->vec_index], prev, sizeof(struct page_region));
+ p->vec_index++;
+ }
+ prev->start = addr;
+ prev->len = len;
+ prev->bitmap = bitmap;
+ p->found_pages += len;
+ } else {
+ return -ENOSPC;
+ }
+ }
+ return 0;
+}
+
+static inline int export_prev_to_out(struct pagemap_scan_private *p, struct page_region __user *vec,
+ unsigned long *vec_index)
+{
+ struct page_region *prev = &p->prev;
+
+ if (prev->len) {
+ if (copy_to_user(&vec[*vec_index], prev, sizeof(struct page_region)))
+ return -EFAULT;
+ p->vec_index++;
+ (*vec_index)++;
+ prev->len = 0;
+ }
+ return 0;
+}
+
+static inline int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long addr,
+ unsigned long end, struct mm_walk *walk)
+{
+ struct pagemap_scan_private *p = walk->private;
+ struct vm_area_struct *vma = walk->vma;
+ unsigned long start = addr;
+ unsigned int len;
+ spinlock_t *ptl;
+ int ret = 0;
+ pte_t *pte;
+ bool pmd_wt;
+
+ if ((walk->vma->vm_end < addr) || (p->max_pages && p->found_pages == p->max_pages))
+ return 0;
+ end = min(end, walk->vma->vm_end);
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ ptl = pmd_trans_huge_lock(pmd, vma);
+ if (ptl) {
+ pmd_wt = !is_pmd_uffd_wp(*pmd);
+ /*
+ * Break huge page into small pages if operation needs to be performed is
+ * on a portion of the huge page or the return buffer cannot store complete
+ * data.
+ */
+ if (pmd_wt && (IS_WP_ENGAGE_OP(p) && (end - addr < HPAGE_SIZE))) {
+ spin_unlock(ptl);
+ split_huge_pmd(vma, pmd, addr);
+ goto process_smaller_pages;
+ }
+ if (IS_GET_OP(p)) {
+ len = (end - addr)/PAGE_SIZE;
+ if (p->max_pages && p->found_pages + len > p->max_pages)
+ len = p->max_pages - p->found_pages;
+
+ ret = add_to_out(pmd_wt, vma->vm_file, pmd_present(*pmd),
+ is_swap_pmd(*pmd), p, addr, len);
+ if (ret) {
+ spin_unlock(ptl);
+ return ret;
+ }
+ }
+ spin_unlock(ptl);
+ if (IS_WP_ENGAGE_OP(p) && pmd_wt) {
+ BUG_ON(start & ~HPAGE_MASK);
+
+ ret = wp_range_async(vma, addr, HPAGE_SIZE);
+ }
+ return ret;
+ }
+process_smaller_pages:
+ if (pmd_trans_unstable(pmd))
+ return 0;
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
+ pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+ for (; addr < end && !ret && (!p->max_pages || (p->found_pages < p->max_pages))
+ ; pte++, addr += PAGE_SIZE) {
+ if (IS_GET_OP(p)) {
+ ret = add_to_out(!is_pte_uffd_wp(*pte), vma->vm_file, pte_present(*pte),
+ is_swap_pte(*pte), p, addr, 1);
+ if (ret)
+ break;
+ }
+ }
+ pte_unmap_unlock(pte - 1, ptl);
+ if (IS_WP_ENGAGE_OP(p)) {
+ BUG_ON(start & ~PAGE_MASK);
+ ret = wp_range_async(vma, start, addr - start);
+ }
+
+ cond_resched();
+ return ret;
+}
+
+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 int len;
+ int ret = 0;
+
+ if (vma) {
+ len = (end - addr)/PAGE_SIZE;
+ if (p->max_pages && p->found_pages + len > p->max_pages)
+ len = p->max_pages - p->found_pages;
+ ret = add_to_out(false, vma->vm_file, false, false, p, addr, len);
+ }
+
+ 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,
+};
+
+static long do_pagemap_cmd(struct mm_struct *mm, struct pagemap_scan_arg *arg)
+{
+ unsigned long empty_slots, vec_index = 0;
+ unsigned long __user start, end;
+ unsigned long __start, __end;
+ struct page_region __user *vec;
+ struct pagemap_scan_private p;
+ int ret;
+
+ start = (unsigned long)untagged_addr(arg->start);
+ vec = (struct page_region *)untagged_addr(arg->vec);
+ if ((!IS_ALIGNED(start, PAGE_SIZE)) || (!access_ok((void __user *)start, arg->len)))
+ return -EINVAL;
+ if (IS_GET_OP(arg) && ((arg->vec_len == 0) ||
+ (!access_ok((void __user *)vec, arg->vec_len * sizeof(struct page_region)))))
+ return -ENOMEM;
+ if ((arg->flags & ~PAGEMAP_WP_ENGAGE) || (arg->required_mask & ~PAGEMAP_OP_MASK) ||
+ (arg->anyof_mask & ~PAGEMAP_OP_MASK) || (arg->excluded_mask & ~PAGEMAP_OP_MASK) ||
+ (arg->return_mask & ~PAGEMAP_OP_MASK))
+ return -EINVAL;
+ if (IS_GET_OP(arg) && ((!arg->required_mask && !arg->anyof_mask && !arg->excluded_mask) ||
+ !arg->return_mask))
+ return -EINVAL;
+ /* The non-WT flags cannot be obtained if PAGEMAP_WP_ENGAGE is also specified. */
+ if (IS_WP_ENGAGE_OP(arg) && ((arg->required_mask & PAGEMAP_NONWT_OP_MASK) ||
+ (arg->anyof_mask & PAGEMAP_NONWT_OP_MASK)))
+ return -EINVAL;
+
+ 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.prev.len = 0;
+ p.vec_len = (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
+
+ if (IS_GET_OP(arg)) {
+ p.vec = kmalloc_array(p.vec_len, sizeof(struct page_region), GFP_KERNEL);
+ if (!p.vec)
+ return -ENOMEM;
+ } else {
+ p.vec = NULL;
+ }
+
+ __start = __end = start;
+ while (__end < end) {
+ p.vec_index = 0;
+ empty_slots = arg->vec_len - vec_index;
+ if (p.vec_len > empty_slots)
+ p.vec_len = empty_slots;
+
+ __end = (__start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK;
+ if (__end > end)
+ __end = end;
+
+ mmap_read_lock(mm);
+ ret = walk_page_range(mm, __start, __end, &pagemap_scan_ops, &p);
+ mmap_read_unlock(mm);
+
+ if (!(!ret || ret == -ENOSPC))
+ goto free_data;
+
+ __start = __end;
+ if (IS_GET_OP(arg) && 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 = export_prev_to_out(&p, vec, &vec_index);
+ if (!ret)
+ ret = vec_index;
+free_data:
+ if (IS_GET_OP(arg))
+ kfree(p.vec);
+
+ return ret;
+}
+
+static long pagemap_scan_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+ struct pagemap_scan_arg __user *uarg = (struct pagemap_scan_arg __user *)arg;
+ struct mm_struct *mm = file->private_data;
+ struct pagemap_scan_arg argument;
+
+ if (cmd == PAGEMAP_SCAN) {
+ if (copy_from_user(&argument, uarg, sizeof(struct pagemap_scan_arg)))
+ return -EFAULT;
+ return do_pagemap_cmd(mm, &argument);
+ }
+ 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/uapi/linux/fs.h b/include/uapi/linux/fs.h
index b7b56871029c..6d03a903a745 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -305,4 +305,54 @@ 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 pagemap_scan_arg)
+
+/* Bits are set in the bitmap of the page_region and masks in pagemap_scan_args */
+#define PAGE_IS_WT (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
+ * bitmap: Bits sets for the region
+ */
+struct page_region {
+ __u64 start;
+ __u64 len;
+ __u64 bitmap;
+};
+
+/*
+ * struct pagemap_scan_arg - Pagemap ioctl argument
+ * @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
+ * @flags: Flags for the IOCTL
+ * @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 pagemap_scan_arg {
+ __u64 start;
+ __u64 len;
+ __u64 vec;
+ __u64 vec_len;
+ __u32 max_pages;
+ __u32 flags;
+ __u64 required_mask;
+ __u64 anyof_mask;
+ __u64 excluded_mask;
+ __u64 return_mask;
+};
+
+/* Special flags */
+#define PAGEMAP_WP_ENGAGE (1 << 0)
+
#endif /* _UAPI_LINUX_FS_H */
diff --git a/tools/include/uapi/linux/fs.h b/tools/include/uapi/linux/fs.h
index b7b56871029c..6d03a903a745 100644
--- a/tools/include/uapi/linux/fs.h
+++ b/tools/include/uapi/linux/fs.h
@@ -305,4 +305,54 @@ 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 pagemap_scan_arg)
+
+/* Bits are set in the bitmap of the page_region and masks in pagemap_scan_args */
+#define PAGE_IS_WT (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
+ * bitmap: Bits sets for the region
+ */
+struct page_region {
+ __u64 start;
+ __u64 len;
+ __u64 bitmap;
+};
+
+/*
+ * struct pagemap_scan_arg - Pagemap ioctl argument
+ * @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
+ * @flags: Flags for the IOCTL
+ * @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 pagemap_scan_arg {
+ __u64 start;
+ __u64 len;
+ __u64 vec;
+ __u64 vec_len;
+ __u32 max_pages;
+ __u32 flags;
+ __u64 required_mask;
+ __u64 anyof_mask;
+ __u64 excluded_mask;
+ __u64 return_mask;
+};
+
+/* Special flags */
+#define PAGEMAP_WP_ENGAGE (1 << 0)
+
#endif /* _UAPI_LINUX_FS_H */
--
2.30.2
