Re: [PATCH v25 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

On 7/17/23 10:26 PM, Andrei Vagin wrote:

On Thu, Jul 13, 2023 at 3:14 AM Muhammad Usama Anjum usama.anjum@collabora.com wrote:

...

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), swapped (PAGE_IS_SWAPPED) or page has pfn zero (PAGE_IS_PFNZERO).
• Find pages which have been written-to and/or write protect the pages (atomic PM_SCAN_OP_GET + PM_SCAN_OP_WP)

This IOCTL can be extended to get information about more PTE bits. The entire address range passed by user [start, end) is scanned until either the user provided buffer is full or max_pages have been found.

Reviewed-by: Andrei Vagin avagin@gmail.com

Thank you.

Here are a few inline comments.

...

Signed-off-by: Muhammad Usama Anjum usama.anjum@collabora.com

Changes in v25:

• Do proper filtering on hole as well (hole got missed earlier)

Changes in v24:

• Place WP markers in case of hole as well

Changes in v23:

• Set vec_buf_index to 0 only when vec_buf_index is set
• Return -EFAULT instead of -EINVAL if vec is NULL
• Correctly return the walk ending address to the page granularity

Changes in v22:

• Interface change to return walk ending address to user:
  • Replace [start start + len) with [start, end)
  • Return the ending address of the address walk in start

Changes in v21:

• Abort walk instead of returning error if WP is to be performed on partial hugetlb
• Changed the data types of some variables in pagemap_scan_private to long

Changes in v20:

• Correct PAGE_IS_FILE and add PAGE_IS_PFNZERO

Changes in v19:

• Interface changes such as renaming, return mask and WP can be used with any flags specified in masks
• Internal code changes

Changes in v18:

• Rebased on top of next-20230613
  • ptep_get() updates
  • remove pmd_trans_unstable() and add ACTION_AGAIN
• Review updates (Micheal)

Changes in v17:

• Rebased on next-20230606
• Made make_uffd_wp_*_pte() better and minor changes

Changes in v16:

• Fixed a corner case where kernel writes beyond user buffer by one element
• Bring back exclusive PM_SCAN_OP_WP
• Cosmetic changes

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

---

fs/proc/task_mmu.c | 591 ++++++++++++++++++++++++++++++++++++++++ include/linux/hugetlb.h | 1 + include/uapi/linux/fs.h | 55 ++++ mm/hugetlb.c | 2 +- 4 files changed, 648 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index cfab855fe7e9..596fdfdc4387 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> @@ -1768,11 +1769,601 @@ static int pagemap_release(struct inode *inode, struct file *file) return 0; }

+#define PM_SCAN_REQUIRE_UFFD (1ULL << 63)

+#define PM_SCAN_FOUND_MAX_PAGES (1) +#define PM_SCAN_END_WALK (-256)

I would add a comment to explain why one is negative and another one is positive.

Sure. I'll add.

...

+#define PM_SCAN_BITS_ALL (PAGE_IS_WRITTEN | PAGE_IS_FILE | \

•                            PAGE_IS_PRESENT | PAGE_IS_SWAPPED |    \
  

•                            PAGE_IS_PFNZERO)
  

+#define PM_SCAN_OPS (PM_SCAN_OP_GET | PM_SCAN_OP_WP) +#define IS_PM_SCAN_GET(flags) (flags & PM_SCAN_OP_GET) +#define IS_PM_SCAN_WP(flags) (flags & PM_SCAN_OP_WP)

+#define PM_SCAN_FLAGS(wt, file, present, swap, pfnzero) \

•   ((wt) | ((file) << 1) | ((present) << 2) |      \
  

•    ((swap) << 3) | ((pfnzero) << 4))
  

it is better to use PAGE_IS_* constants here

#define PAGE_IS_PFNZERO (1 << 4) PAGE_IS_PFNZERO macro cannot be used here.

...

+struct pagemap_scan_private {

•   struct page_region *vec_buf, cur_buf;
  

•   unsigned long vec_buf_len, vec_buf_index, max_pages, found_pages;
  

•   unsigned long long flags, required_mask, anyof_mask, excluded_mask, return_mask, end_addr;
  

end_addr has to be unsigned long.

Sure.

...

+};

+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 = ptep_get(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);
  

•   } else {
  

•           set_pte_at(vma->vm_mm, addr, pte,
  

•                      make_pte_marker(PTE_MARKER_UFFD_WP));
  

•   }
  

+}

+static inline bool pagemap_scan_is_file(struct vm_area_struct *vma, pte_t ptent,

•                                   unsigned long addr)
  

+{

•   struct page *page = NULL;
  

•   swp_entry_t entry;
  

•   if (pte_present(ptent)) {
  

•           page = vm_normal_page(vma, addr, ptent);
  

•   } else {
  

•           entry = pte_to_swp_entry(ptent);
  

•           if (is_pfn_swap_entry(entry))
  

•                   page = pfn_swap_entry_to_page(entry);
  

•   }
  

•   if (page && !PageAnon(page))
  

•           return true;
  

•   return false;
  

+}

+#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)
  

+{

•   if (is_hugetlb_entry_hwpoisoned(ptent) || is_pte_marker(ptent))
  

•           return;
  

•   if (is_hugetlb_entry_migration(ptent))
  

•           set_huge_pte_at(vma->vm_mm, addr, ptep,
  

•                           pte_swp_mkuffd_wp(ptent));
  

•   else if (!huge_pte_none(ptent))
  

•           huge_ptep_modify_prot_commit(vma, addr, ptep, ptent,
  

•                                        huge_pte_mkuffd_wp(ptent));
  

•   else
  

•           set_huge_pte_at(vma->vm_mm, addr, ptep,
  

•                           make_pte_marker(PTE_MARKER_UFFD_WP));
  

+}

+static inline bool pagemap_scan_is_huge_file(pte_t pte) +{

•   if (pte_present(pte) && (!PageAnon(pte_page(pte))))
  

•           return true;
  

•   return false;
  

+} +#endif

+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 ((p->flags & PM_SCAN_REQUIRE_UFFD) && (!userfaultfd_wp_async(vma) ||
  

•       !userfaultfd_wp_use_markers(vma)))
  

•           return -EPERM;
  

•   if (vma->vm_flags & VM_PFNMAP)
  

•           return 1;
  

•   return 0;
  

+}

+static int pagemap_scan_output(unsigned long bitmap,

•                          struct pagemap_scan_private *p,
  

•                          unsigned long addr, unsigned int n_pages)
  

+{

•   struct page_region *cur_buf = &p->cur_buf;
  

•   bitmap &= p->return_mask;
  

•   if (cur_buf->flags == bitmap &&
  

•       cur_buf->start + cur_buf->len * PAGE_SIZE == addr) {
  

•           cur_buf->len += n_pages;
  

•           p->found_pages += n_pages;
  

•   } else {
  

•           if (cur_buf->len) {
  

•                   if (p->vec_buf_index >= p->vec_buf_len) {
  

•                           p->end_addr = addr;
  

•                           return PM_SCAN_END_WALK;
  

•                   }
  

•                   memcpy(&p->vec_buf[p->vec_buf_index], cur_buf,
  

•                          sizeof(*p->vec_buf));
  

•                   p->vec_buf_index++;
  

•           }
  

•           cur_buf->start = addr;
  

•           cur_buf->len = n_pages;
  

•           cur_buf->flags = bitmap;
  

•           p->found_pages += n_pages;
  

•   }
  

•   if (p->found_pages == p->max_pages) {
  

•           p->end_addr = addr + n_pages * PAGE_SIZE;
  

•           return PM_SCAN_FOUND_MAX_PAGES;
  

•   }
  

•   return 0;
  

+}

+static bool pagemap_scan_is_interesting_page(unsigned long bitmap,

•                                        struct pagemap_scan_private *p)
  

+{

•   if ((p->required_mask & bitmap) != p->required_mask)
  

•           return false;
  

•   if (p->anyof_mask && !(p->anyof_mask & bitmap))
  

•           return false;
  

•   if (p->excluded_mask & bitmap)
  

•           return false;
  

•   return true;
  

+}

+static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,

•                             unsigned long end, struct mm_walk *walk)
  

+{

•   bool is_written, flush = false, 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 (n_pages > p->max_pages - p->found_pages)
  

•                   n_pages = p->max_pages - p->found_pages;
  

•           is_written = !is_pmd_uffd_wp(*pmd);
  

•           bitmap = PM_SCAN_FLAGS(is_written, false,
  

•                                  pmd_present(*pmd), is_swap_pmd(*pmd),
  

•                                  pmd_present(*pmd) && is_zero_pfn(pmd_pfn(*pmd)));
  

•           if (IS_PM_SCAN_GET(p->flags))
  

•                   interesting = pagemap_scan_is_interesting_page(bitmap, p);
  

•           if (interesting) {
  

•                   /*
  

•                    * 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;
  

•                   }
  

•                   if (IS_PM_SCAN_GET(p->flags))
  

•                           ret = pagemap_scan_output(bitmap, p, start, n_pages);
  

•                   if (IS_PM_SCAN_WP(p->flags) && is_written && 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) {
  

•           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, pagemap_scan_is_file(vma, ptent, addr),
  

•                                  pte_present(ptent), is_swap_pte(ptent),
  

•                                  pte_present(ptent) && is_zero_pfn(pte_pfn(ptent)));
  

•           if (IS_PM_SCAN_GET(p->flags)) {
  

•                   interesting = pagemap_scan_is_interesting_page(bitmap, p);
  

•                   if (interesting)
  

•                           ret = pagemap_scan_output(bitmap, p, addr, 1);
  

•           }
  

•           if (IS_PM_SCAN_WP(p->flags) && is_written && interesting &&
  

•               ret >= 0) {
  

•                   make_uffd_wp_pte(vma, addr, pte);
  

•                   flush = true;
  

•           }
  

•   }
  

•   if (flush)
  

•           flush_tlb_range(vma, start, addr);
  

•   pte_unmap_unlock(orig_pte, ptl);
  

•   arch_leave_lazy_mmu_mode();
  

•   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;
  

•   bool is_written, interesting = true;
  

•   struct hstate *h = hstate_vma(vma);
  

•   unsigned long bitmap;
  

•   spinlock_t *ptl;
  

•   int ret = 0;
  

•   pte_t ptent;
  

•   if (IS_PM_SCAN_WP(p->flags) && n_pages < HPAGE_SIZE/PAGE_SIZE) {
  

•           p->end_addr = start;
  

•           return -EINVAL;
  

•   }
  

•   if (n_pages > p->max_pages - p->found_pages)
  

•           n_pages = p->max_pages - p->found_pages;
  

•   if (IS_PM_SCAN_WP(p->flags)) {
  

•           i_mmap_lock_write(vma->vm_file->f_mapping);
  

•           ptl = huge_pte_lock(h, vma->vm_mm, ptep);
  

•   }
  

•   ptent = huge_ptep_get(ptep);
  

•   is_written = !is_huge_pte_uffd_wp(ptent);
  

•   bitmap = PM_SCAN_FLAGS(is_written, pagemap_scan_is_huge_file(ptent),
  

•                          pte_present(ptent), is_swap_pte(ptent),
  

•                          pte_present(ptent) && is_zero_pfn(pte_pfn(ptent)));
  

•   if (IS_PM_SCAN_GET(p->flags))
  

•           interesting = pagemap_scan_is_interesting_page(bitmap, p);
  

•   if (interesting) {
  

•           /*
  

•            * Partial hugetlb page clear isn't supported
  

•            */
  

•           if (is_written && IS_PM_SCAN_WP(p->flags) &&
  

•               n_pages < HPAGE_SIZE/PAGE_SIZE) {
  

•                   ret = PM_SCAN_END_WALK;
  

•                   p->end_addr = start;
  

•                   goto unlock_and_return;
  

•           }
  

•           if (IS_PM_SCAN_GET(p->flags))
  

•                   ret = pagemap_scan_output(bitmap, p, start, n_pages);
  

•           if (IS_PM_SCAN_WP(p->flags) && is_written && ret >= 0) {
  

•                   make_uffd_wp_huge_pte(vma, start, ptep, ptent);
  

•                   flush_hugetlb_tlb_range(vma, start, end);
  

•           }
  

•   }
  

+unlock_and_return:

•   if (IS_PM_SCAN_WP(p->flags)) {
  

•           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;
  

•   bool interesting = true;
  

•   unsigned long bitmap;
  

•   int ret = 0;
  

•   if (!vma)
  

•           return 0;
  

•   bitmap = PM_SCAN_FLAGS(false, false, false, false, false);
  

•   if (IS_PM_SCAN_GET(p->flags))
  

•           interesting = pagemap_scan_is_interesting_page(bitmap, p);
  

•   if (interesting) {
  

•           if (IS_PM_SCAN_GET(p->flags)) {
  

•                   if (n_pages > p->max_pages - p->found_pages)
  

•                           n_pages = p->max_pages - p->found_pages;
  

•                   ret = pagemap_scan_output(bitmap, p, addr, n_pages);
  

•           }
  

•           if (IS_PM_SCAN_WP(p->flags) && !ret &&
  

•               uffd_wp_range(vma, addr, end - addr, true) < 0)
  

Why do we need to call uffd_wp_range for holes? Should we call flush_tlb_range after it?

...

•                   ret = -EINVAL;
  

•   }
  

•   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,

•                              unsigned long end, 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)
  

•           return -EINVAL;
  

•   if (arg->flags & ~PM_SCAN_OPS)
  

•           return -EINVAL;
  

•   if (!(end - start))
  

•           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 range */
  

•   if (!IS_ALIGNED(start, PAGE_SIZE))
  

•           return -EINVAL;
  

•   if (!access_ok((void __user *)start, end - start))
  

•           return -EFAULT;
  

•   if (IS_PM_SCAN_GET(arg->flags)) {
  

•           if (arg->vec_len == 0)
  

•                   return -EINVAL;
  

•           if (!vec)
  

•                   return -EFAULT;
  

•           if (!access_ok((void __user *)vec,
  

•                          arg->vec_len * sizeof(struct page_region)))
  

•                   return -EFAULT;
  

•   }
  

•   if (IS_PM_SCAN_WP(arg->flags) && !IS_PM_SCAN_GET(arg->flags) &&
  

•       arg->max_pages)
  

•           return -EINVAL;
  

•   return 0;
  

+}

+static long do_pagemap_scan(struct mm_struct *mm, unsigned long __arg) +{

•   struct pm_scan_arg __user *uarg = (struct pm_scan_arg __user *)__arg;
  

•   unsigned long 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);
  

•   end = untagged_addr((unsigned long)arg.end);
  

•   vec = (struct page_region __user *)untagged_addr((unsigned long)arg.vec);
  

•   ret = pagemap_scan_args_valid(&arg, start, end, vec);
  

•   if (ret)
  

•           return ret;
  

•   p.max_pages = (arg.max_pages) ? arg.max_pages : ULONG_MAX;
  

•   p.found_pages = 0;
  

•   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.flags = arg.flags;
  

•   p.flags |= ((p.required_mask | p.anyof_mask | p.excluded_mask) &
  

•               PAGE_IS_WRITTEN) ? PM_SCAN_REQUIRE_UFFD : 0;
  

•   p.cur_buf.start = p.cur_buf.len = p.cur_buf.flags = 0;
  

•   p.vec_buf = NULL;
  

•   p.vec_buf_len = PAGEMAP_WALK_SIZE >> PAGE_SHIFT;
  

•   p.vec_buf_index = 0;
  

•   p.end_addr = 0;
  

•   /*
  

•    * 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_buf between different walks and
  

•    * store the p.cur_buf at the end of the walk to the user buffer.
  

•    */
  

•   if (IS_PM_SCAN_GET(p.flags)) {
  

•           p.vec_buf = kmalloc_array(p.vec_buf_len, sizeof(*p.vec_buf),
  

•                                     GFP_KERNEL);
  

•           if (!p.vec_buf)
  

•                   return -ENOMEM;
  

•   }
  

•   /*
  

•    * Protection change for the range is going to happen.
  

•    */
  

•   if (IS_PM_SCAN_WP(p.flags)) {
  

•           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) {
  

•           if (IS_PM_SCAN_GET(p.flags)) {
  

•                   /*
  

•                    * All data is copied to cur_buf first. When more data
  

•                    * is found, we push cur_buf to vec_buf and copy new
  

•                    * data to cur_buf. Subtract 1 from length as the
  

•                    * index of cur_buf isn't counted in length.
  

•                    */
  

•                   empty_slots = arg.vec_len - vec_index;
  

•                   p.vec_buf_len = min(p.vec_buf_len, empty_slots - 1);
  

•           }
  

I still don't understand why we don't want/need to check for pending signals.

We haven't added it as other existing code such as mincore() and pagemap_read() don't have it either. Also mmap_read_lock_killable would return error if there is some critical single pending.

...

•           ret = mmap_read_lock_killable(mm);
  

•           if (ret)
  

•                   goto out;
  

•           walk_end = min((walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK, end);
  

•           ret = walk_page_range(mm, walk_start, walk_end,
  

•                                 &pagemap_scan_ops, &p);
  

•           mmap_read_unlock(mm);
  

•           if (ret == PM_SCAN_FOUND_MAX_PAGES || ret == PM_SCAN_END_WALK)
  

•                   arg.start = p.end_addr;
  

nit: this check can be moved out of the loop.

No, ret could get replaced by error if copy_to_user() fails. So we have to do this before that.

...

•           if (ret && ret != PM_SCAN_FOUND_MAX_PAGES &&
  

•               ret != PM_SCAN_END_WALK)
  

•                   goto out;
  

•           if (p.vec_buf_index) {
  

•                   if (copy_to_user(&vec[vec_index], p.vec_buf,
  

•                                    p.vec_buf_index * sizeof(*p.vec_buf))) {
  

•                           /*
  

•                            * Return error even though the OP succeeded
  

•                            */
  

•                           ret = -EFAULT;
  

•                           goto out;
  

•                   }
  

•                   vec_index += p.vec_buf_index;
  

•                   p.vec_buf_index = 0;
  

•           }
  

•           walk_start = walk_end;
  

•   }
  

•   if (p.cur_buf.len) {
  

•           if (copy_to_user(&vec[vec_index], &p.cur_buf, sizeof(p.cur_buf))) {
  

•                   ret = -EFAULT;
  

•                   goto out;
  

•           }
  

•           vec_index++;
  

•   }
  

•   ret = vec_index;
  

+out:

•   if (!p.end_addr)
  

•           arg.start = walk_start;
  

•   if (copy_to_user(&uarg->start, &arg.start, sizeof(arg.start)))
  

•           ret = -EFAULT;
  

•   if (IS_PM_SCAN_WP(p.flags))
  

•           mmu_notifier_invalidate_range_end(&range);
  

•   kfree(p.vec_buf);
  

•   return ret;
  

+}

+static long do_pagemap_cmd(struct file *file, unsigned int cmd,

•                      unsigned long arg)
  

+{

•   struct mm_struct *mm = file->private_data;
  

•   switch (cmd) {
  

•   case PAGEMAP_SCAN:
  

•           return do_pagemap_scan(mm, arg);
  

•   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/linux/hugetlb.h b/include/linux/hugetlb.h index 623e98d62df3..c44e7bde0339 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -259,6 +259,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma, unsigned long cp_flags);

bool is_hugetlb_entry_migration(pte_t pte); +bool is_hugetlb_entry_hwpoisoned(pte_t pte); void hugetlb_unshare_all_pmds(struct vm_area_struct *vma);

#else /* !CONFIG_HUGETLB_PAGE */ diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index b7b56871029c..ac684d99e68f 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -305,4 +305,59 @@ 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 flags 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) +#define PAGE_IS_PFNZERO (1 << 4)

+/*

• • struct page_region - Page region with 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 flags;
  

+};

+/*

• • struct pm_scan_arg - Pagemap ioctl argument
• • @size: Size of the structure
• • @flags: Flags for the IOCTL
• • @start: Starting address of the region

• •                 (Ending address of the walk is also returned in it)
    

• • @end: Ending address of the region
• • @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 end;
  

•   __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 */ diff --git a/mm/hugetlb.c b/mm/hugetlb.c index ee88a2a6649f..f7cefdcb114c 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4981,7 +4981,7 @@ bool is_hugetlb_entry_migration(pte_t pte) return false; }

-static bool is_hugetlb_entry_hwpoisoned(pte_t pte) +bool is_hugetlb_entry_hwpoisoned(pte_t pte) { swp_entry_t swp;

-- 2.39.2