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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  *  Copyright (C) 2009  Red Hat, Inc.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/mm.h>
 #include <linux/sched.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/coredump.h>
 #include <linux/sched/numa_balancing.h>
 #include <linux/highmem.h>
 #include <linux/hugetlb.h>
 #include <linux/mmu_notifier.h>
 #include <linux/rmap.h>
 #include <linux/swap.h>
 #include <linux/shrinker.h>
 #include <linux/mm_inline.h>
 #include <linux/swapops.h>
 #include <linux/backing-dev.h>
 #include <linux/dax.h>
 #include <linux/khugepaged.h>
 #include <linux/freezer.h>
 #include <linux/pfn_t.h>
 #include <linux/mman.h>
 #include <linux/memremap.h>
 #include <linux/pagemap.h>
 #include <linux/debugfs.h>
 #include <linux/migrate.h>
 #include <linux/hashtable.h>
 #include <linux/userfaultfd_k.h>
 #include <linux/page_idle.h>
 #include <linux/shmem_fs.h>
 #include <linux/oom.h>
 #include <linux/numa.h>
 #include <linux/page_owner.h>
 #include <linux/sched/sysctl.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
 #include "internal.h"
 #include "swap.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/thp.h>
 
 /*
  * By default, transparent hugepage support is disabled in order to avoid
  * risking an increased memory footprint for applications that are not
  * guaranteed to benefit from it. When transparent hugepage support is
  * enabled, it is for all mappings, and khugepaged scans all mappings.
  * Defrag is invoked by khugepaged hugepage allocations and by page faults
  * for all hugepage allocations.
  */
 unsigned long transparent_hugepage_flags __read_mostly =
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
     (1<<TRANSPARENT_HUGEPAGE_FLAG)|
 #endif
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
     (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
 #endif
     (1<<TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG)|
     (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
     (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 
 static struct shrinker deferred_split_shrinker;
 
 static atomic_t huge_zero_refcount;
 struct page *huge_zero_page __read_mostly;
 unsigned long huge_zero_pfn __read_mostly = ~0UL;
 
 bool hugepage_vma_check(struct vm_area_struct *vma,
             unsigned long vm_flags,
             bool smaps, bool in_pf)
 {
     if (!vma->vm_mm)        /* vdso */
         return false;
 
     /*
      * Explicitly disabled through madvise or prctl, or some
      * architectures may disable THP for some mappings, for
      * example, s390 kvm.
      * */
     if ((vm_flags & VM_NOHUGEPAGE) ||
         test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
         return false;
     /*
      * If the hardware/firmware marked hugepage support disabled.
      */
     if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_NEVER_DAX))
         return false;
 
     /* khugepaged doesn't collapse DAX vma, but page fault is fine. */
     if (vma_is_dax(vma))
         return in_pf;
 
     /*
      * Special VMA and hugetlb VMA.
      * Must be checked after dax since some dax mappings may have
      * VM_MIXEDMAP set.
      */
     if (vm_flags & VM_NO_KHUGEPAGED)
         return false;
 
     /*
      * Check alignment for file vma and size for both file and anon vma.
      *
      * Skip the check for page fault. Huge fault does the check in fault
      * handlers. And this check is not suitable for huge PUD fault.
      */
     if (!in_pf &&
         !transhuge_vma_suitable(vma, (vma->vm_end - HPAGE_PMD_SIZE)))
         return false;
 
     /*
      * Enabled via shmem mount options or sysfs settings.
      * Must be done before hugepage flags check since shmem has its
      * own flags.
      */
     if (!in_pf && shmem_file(vma->vm_file))
         return shmem_huge_enabled(vma);
 
     if (!hugepage_flags_enabled())
         return false;
 
     /* THP settings require madvise. */
     if (!(vm_flags & VM_HUGEPAGE) && !hugepage_flags_always())
         return false;
 
     /* Only regular file is valid */
     if (!in_pf && file_thp_enabled(vma))
         return true;
 
     if (!vma_is_anonymous(vma))
         return false;
 
     if (vma_is_temporary_stack(vma))
         return false;
 
     /*
      * THPeligible bit of smaps should show 1 for proper VMAs even
      * though anon_vma is not initialized yet.
      *
      * Allow page fault since anon_vma may be not initialized until
      * the first page fault.
      */
     if (!vma->anon_vma)
         return (smaps || in_pf);
 
     return true;
 }
 
 static bool get_huge_zero_page(void)
 {
     struct page *zero_page;
 retry:
     if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
         return true;
 
     zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
             HPAGE_PMD_ORDER);
     if (!zero_page) {
         count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
         return false;
     }
     count_vm_event(THP_ZERO_PAGE_ALLOC);
     preempt_disable();
     if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
         preempt_enable();
         __free_pages(zero_page, compound_order(zero_page));
         goto retry;
     }
     WRITE_ONCE(huge_zero_pfn, page_to_pfn(zero_page));
 
     /* We take additional reference here. It will be put back by shrinker */
     atomic_set(&huge_zero_refcount, 2);
     preempt_enable();
     return true;
 }
 
 static void put_huge_zero_page(void)
 {
     /*
      * Counter should never go to zero here. Only shrinker can put
      * last reference.
      */
     BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
 }
 
 struct page *mm_get_huge_zero_page(struct mm_struct *mm)
 {
     if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
         return READ_ONCE(huge_zero_page);
 
     if (!get_huge_zero_page())
         return NULL;
 
     if (test_and_set_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
         put_huge_zero_page();
 
     return READ_ONCE(huge_zero_page);
 }
 
 void mm_put_huge_zero_page(struct mm_struct *mm)
 {
     if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
         put_huge_zero_page();
 }
 
 static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
                     struct shrink_control *sc)
 {
     /* we can free zero page only if last reference remains */
     return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
 }
 
 static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
                        struct shrink_control *sc)
 {
     if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
         struct page *zero_page = xchg(&huge_zero_page, NULL);
         BUG_ON(zero_page == NULL);
         WRITE_ONCE(huge_zero_pfn, ~0UL);
         __free_pages(zero_page, compound_order(zero_page));
         return HPAGE_PMD_NR;
     }
 
     return 0;
 }
 
 static struct shrinker huge_zero_page_shrinker = {
     .count_objects = shrink_huge_zero_page_count,
     .scan_objects = shrink_huge_zero_page_scan,
     .seeks = DEFAULT_SEEKS,
 };
 
 #ifdef CONFIG_SYSFS
 static ssize_t enabled_show(struct kobject *kobj,
                 struct kobj_attribute *attr, char *buf)
 {
     const char *output;
 
     if (test_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags))
         output = "[always] madvise never";
     else if (test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
               &transparent_hugepage_flags))
         output = "always [madvise] never";
     else
         output = "always madvise [never]";
 
     return sysfs_emit(buf, "%s\n", output);
 }
 
 static ssize_t enabled_store(struct kobject *kobj,
                  struct kobj_attribute *attr,
                  const char *buf, size_t count)
 {
     ssize_t ret = count;
 
     if (sysfs_streq(buf, "always")) {
         clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
         set_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
     } else if (sysfs_streq(buf, "madvise")) {
         clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
         set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
     } else if (sysfs_streq(buf, "never")) {
         clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
     } else
         ret = -EINVAL;
 
     if (ret > 0) {
         int err = start_stop_khugepaged();
         if (err)
             ret = err;
     }
     return ret;
 }
 
 static struct kobj_attribute enabled_attr = __ATTR_RW(enabled);
 
 ssize_t single_hugepage_flag_show(struct kobject *kobj,
                   struct kobj_attribute *attr, char *buf,
                   enum transparent_hugepage_flag flag)
 {
     return sysfs_emit(buf, "%d\n",
               !!test_bit(flag, &transparent_hugepage_flags));
 }
 
 ssize_t single_hugepage_flag_store(struct kobject *kobj,
                  struct kobj_attribute *attr,
                  const char *buf, size_t count,
                  enum transparent_hugepage_flag flag)
 {
     unsigned long value;
     int ret;
 
     ret = kstrtoul(buf, 10, &value);
     if (ret < 0)
         return ret;
     if (value > 1)
         return -EINVAL;
 
     if (value)
         set_bit(flag, &transparent_hugepage_flags);
     else
         clear_bit(flag, &transparent_hugepage_flags);
 
     return count;
 }
 
 static ssize_t defrag_show(struct kobject *kobj,
                struct kobj_attribute *attr, char *buf)
 {
     const char *output;
 
     if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
              &transparent_hugepage_flags))
         output = "[always] defer defer+madvise madvise never";
     else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
               &transparent_hugepage_flags))
         output = "always [defer] defer+madvise madvise never";
     else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG,
               &transparent_hugepage_flags))
         output = "always defer [defer+madvise] madvise never";
     else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
               &transparent_hugepage_flags))
         output = "always defer defer+madvise [madvise] never";
     else
         output = "always defer defer+madvise madvise [never]";
 
     return sysfs_emit(buf, "%s\n", output);
 }
 
 static ssize_t defrag_store(struct kobject *kobj,
                 struct kobj_attribute *attr,
                 const char *buf, size_t count)
 {
     if (sysfs_streq(buf, "always")) {
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
         set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
     } else if (sysfs_streq(buf, "defer+madvise")) {
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
         set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
     } else if (sysfs_streq(buf, "defer")) {
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
         set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
     } else if (sysfs_streq(buf, "madvise")) {
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
         set_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
     } else if (sysfs_streq(buf, "never")) {
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags);
     } else
         return -EINVAL;
 
     return count;
 }
 static struct kobj_attribute defrag_attr = __ATTR_RW(defrag);
 
 static ssize_t use_zero_page_show(struct kobject *kobj,
                   struct kobj_attribute *attr, char *buf)
 {
     return single_hugepage_flag_show(kobj, attr, buf,
                      TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 }
 static ssize_t use_zero_page_store(struct kobject *kobj,
         struct kobj_attribute *attr, const char *buf, size_t count)
 {
     return single_hugepage_flag_store(kobj, attr, buf, count,
                  TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 }
 static struct kobj_attribute use_zero_page_attr = __ATTR_RW(use_zero_page);
 
 static ssize_t hpage_pmd_size_show(struct kobject *kobj,
                    struct kobj_attribute *attr, char *buf)
 {
     return sysfs_emit(buf, "%lu\n", HPAGE_PMD_SIZE);
 }
 static struct kobj_attribute hpage_pmd_size_attr =
     __ATTR_RO(hpage_pmd_size);
 
 static struct attribute *hugepage_attr[] = {
     &enabled_attr.attr,
     &defrag_attr.attr,
     &use_zero_page_attr.attr,
     &hpage_pmd_size_attr.attr,
 #ifdef CONFIG_SHMEM
     &shmem_enabled_attr.attr,
 #endif
     NULL,
 };
 
 static const struct attribute_group hugepage_attr_group = {
     .attrs = hugepage_attr,
 };
 
 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
 {
     int err;
 
     *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
     if (unlikely(!*hugepage_kobj)) {
         pr_err("failed to create transparent hugepage kobject\n");
         return -ENOMEM;
     }
 
     err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
     if (err) {
         pr_err("failed to register transparent hugepage group\n");
         goto delete_obj;
     }
 
     err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
     if (err) {
         pr_err("failed to register transparent hugepage group\n");
         goto remove_hp_group;
     }
 
     return 0;
 
 remove_hp_group:
     sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
 delete_obj:
     kobject_put(*hugepage_kobj);
     return err;
 }
 
 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 {
     sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
     sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
     kobject_put(hugepage_kobj);
 }
 #else
 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
 {
     return 0;
 }
 
 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 {
 }
 #endif /* CONFIG_SYSFS */
 
 static int __init hugepage_init(void)
 {
     int err;
     struct kobject *hugepage_kobj;
 
     if (!has_transparent_hugepage()) {
         /*
          * Hardware doesn't support hugepages, hence disable
          * DAX PMD support.
          */
         transparent_hugepage_flags = 1 << TRANSPARENT_HUGEPAGE_NEVER_DAX;
         return -EINVAL;
     }
 
     /*
      * hugepages can't be allocated by the buddy allocator
      */
     MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER >= MAX_ORDER);
     /*
      * we use page->mapping and page->index in second tail page
      * as list_head: assuming THP order >= 2
      */
     MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER < 2);
 
     err = hugepage_init_sysfs(&hugepage_kobj);
     if (err)
         goto err_sysfs;
 
     err = khugepaged_init();
     if (err)
         goto err_slab;
 
     err = register_shrinker(&huge_zero_page_shrinker, "thp-zero");
     if (err)
         goto err_hzp_shrinker;
     err = register_shrinker(&deferred_split_shrinker, "thp-deferred_split");
     if (err)
         goto err_split_shrinker;
 
     /*
      * By default disable transparent hugepages on smaller systems,
      * where the extra memory used could hurt more than TLB overhead
      * is likely to save.  The admin can still enable it through /sys.
      */
     if (totalram_pages() < (512 << (20 - PAGE_SHIFT))) {
         transparent_hugepage_flags = 0;
         return 0;
     }
 
     err = start_stop_khugepaged();
     if (err)
         goto err_khugepaged;
 
     return 0;
 err_khugepaged:
     unregister_shrinker(&deferred_split_shrinker);
 err_split_shrinker:
     unregister_shrinker(&huge_zero_page_shrinker);
 err_hzp_shrinker:
     khugepaged_destroy();
 err_slab:
     hugepage_exit_sysfs(hugepage_kobj);
 err_sysfs:
     return err;
 }
 subsys_initcall(hugepage_init);
 
 static int __init setup_transparent_hugepage(char *str)
 {
     int ret = 0;
     if (!str)
         goto out;
     if (!strcmp(str, "always")) {
         set_bit(TRANSPARENT_HUGEPAGE_FLAG,
             &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
               &transparent_hugepage_flags);
         ret = 1;
     } else if (!strcmp(str, "madvise")) {
         clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
               &transparent_hugepage_flags);
         set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
             &transparent_hugepage_flags);
         ret = 1;
     } else if (!strcmp(str, "never")) {
         clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
               &transparent_hugepage_flags);
         clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
               &transparent_hugepage_flags);
         ret = 1;
     }
 out:
     if (!ret)
         pr_warn("transparent_hugepage= cannot parse, ignored\n");
     return ret;
 }
 __setup("transparent_hugepage=", setup_transparent_hugepage);
 
 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 {
     if (likely(vma->vm_flags & VM_WRITE))
         pmd = pmd_mkwrite(pmd);
     return pmd;
 }
 
 #ifdef CONFIG_MEMCG
 static inline struct deferred_split *get_deferred_split_queue(struct page *page)
 {
     struct mem_cgroup *memcg = page_memcg(compound_head(page));
     struct pglist_data *pgdat = NODE_DATA(page_to_nid(page));
 
     if (memcg)
         return &memcg->deferred_split_queue;
     else
         return &pgdat->deferred_split_queue;
 }
 #else
 static inline struct deferred_split *get_deferred_split_queue(struct page *page)
 {
     struct pglist_data *pgdat = NODE_DATA(page_to_nid(page));
 
     return &pgdat->deferred_split_queue;
 }
 #endif
 
 void prep_transhuge_page(struct page *page)
 {
     /*
      * we use page->mapping and page->index in second tail page
      * as list_head: assuming THP order >= 2
      */
 
     INIT_LIST_HEAD(page_deferred_list(page));
     set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
 }
 
 static inline bool is_transparent_hugepage(struct page *page)
 {
     if (!PageCompound(page))
         return false;
 
     page = compound_head(page);
     return is_huge_zero_page(page) ||
            page[1].compound_dtor == TRANSHUGE_PAGE_DTOR;
 }
 
 static unsigned long __thp_get_unmapped_area(struct file *filp,
         unsigned long addr, unsigned long len,
         loff_t off, unsigned long flags, unsigned long size)
 {
     loff_t off_end = off + len;
     loff_t off_align = round_up(off, size);
     unsigned long len_pad, ret;
 
     if (off_end <= off_align || (off_end - off_align) < size)
         return 0;
 
     len_pad = len + size;
     if (len_pad < len || (off + len_pad) < off)
         return 0;
 
     ret = current->mm->get_unmapped_area(filp, addr, len_pad,
                           off >> PAGE_SHIFT, flags);
 
     /*
      * The failure might be due to length padding. The caller will retry
      * without the padding.
      */
     if (IS_ERR_VALUE(ret))
         return 0;
 
     /*
      * Do not try to align to THP boundary if allocation at the address
      * hint succeeds.
      */
     if (ret == addr)
         return addr;
 
     ret += (off - ret) & (size - 1);
     return ret;
 }
 
 unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
         unsigned long len, unsigned long pgoff, unsigned long flags)
 {
     unsigned long ret;
     loff_t off = (loff_t)pgoff << PAGE_SHIFT;
 
     ret = __thp_get_unmapped_area(filp, addr, len, off, flags, PMD_SIZE);
     if (ret)
         return ret;
 
     return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
 }
 EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
 
 static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
             struct page *page, gfp_t gfp)
 {
     struct vm_area_struct *vma = vmf->vma;
     pgtable_t pgtable;
     unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
     vm_fault_t ret = 0;
 
     VM_BUG_ON_PAGE(!PageCompound(page), page);
 
     if (mem_cgroup_charge(page_folio(page), vma->vm_mm, gfp)) {
         put_page(page);
         count_vm_event(THP_FAULT_FALLBACK);
         count_vm_event(THP_FAULT_FALLBACK_CHARGE);
         return VM_FAULT_FALLBACK;
     }
     cgroup_throttle_swaprate(page, gfp);
 
     pgtable = pte_alloc_one(vma->vm_mm);
     if (unlikely(!pgtable)) {
         ret = VM_FAULT_OOM;
         goto release;
     }
 
     clear_huge_page(page, vmf->address, HPAGE_PMD_NR);
     /*
      * The memory barrier inside __SetPageUptodate makes sure that
      * clear_huge_page writes become visible before the set_pmd_at()
      * write.
      */
     __SetPageUptodate(page);
 
     vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
     if (unlikely(!pmd_none(*vmf->pmd))) {
         goto unlock_release;
     } else {
         pmd_t entry;
 
         ret = check_stable_address_space(vma->vm_mm);
         if (ret)
             goto unlock_release;
 
         /* Deliver the page fault to userland */
         if (userfaultfd_missing(vma)) {
             spin_unlock(vmf->ptl);
             put_page(page);
             pte_free(vma->vm_mm, pgtable);
             ret = handle_userfault(vmf, VM_UFFD_MISSING);
             VM_BUG_ON(ret & VM_FAULT_FALLBACK);
             return ret;
         }
 
         entry = mk_huge_pmd(page, vma->vm_page_prot);
         entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
         page_add_new_anon_rmap(page, vma, haddr);
         lru_cache_add_inactive_or_unevictable(page, vma);
         pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
         set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
         update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
         add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
         mm_inc_nr_ptes(vma->vm_mm);
         spin_unlock(vmf->ptl);
         count_vm_event(THP_FAULT_ALLOC);
         count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
     }
 
     return 0;
 unlock_release:
     spin_unlock(vmf->ptl);
 release:
     if (pgtable)
         pte_free(vma->vm_mm, pgtable);
     put_page(page);
     return ret;
 
 }
 
 /*
  * always: directly stall for all thp allocations
  * defer: wake kswapd and fail if not immediately available
  * defer+madvise: wake kswapd and directly stall for MADV_HUGEPAGE, otherwise
  *        fail if not immediately available
  * madvise: directly stall for MADV_HUGEPAGE, otherwise fail if not immediately
  *      available
  * never: never stall for any thp allocation
  */
 gfp_t vma_thp_gfp_mask(struct vm_area_struct *vma)
 {
     const bool vma_madvised = vma && (vma->vm_flags & VM_HUGEPAGE);
 
     /* Always do synchronous compaction */
     if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
         return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY);
 
     /* Kick kcompactd and fail quickly */
     if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
         return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM;
 
     /* Synchronous compaction if madvised, otherwise kick kcompactd */
     if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, &transparent_hugepage_flags))
         return GFP_TRANSHUGE_LIGHT |
             (vma_madvised ? __GFP_DIRECT_RECLAIM :
                     __GFP_KSWAPD_RECLAIM);
 
     /* Only do synchronous compaction if madvised */
     if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
         return GFP_TRANSHUGE_LIGHT |
                (vma_madvised ? __GFP_DIRECT_RECLAIM : 0);
 
     return GFP_TRANSHUGE_LIGHT;
 }
 
 /* Caller must hold page table lock. */
 static void set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
         struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
         struct page *zero_page)
 {
     pmd_t entry;
     if (!pmd_none(*pmd))
         return;
     entry = mk_pmd(zero_page, vma->vm_page_prot);
     entry = pmd_mkhuge(entry);
     if (pgtable)
         pgtable_trans_huge_deposit(mm, pmd, pgtable);
     set_pmd_at(mm, haddr, pmd, entry);
     mm_inc_nr_ptes(mm);
 }
 
 vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
 {
     struct vm_area_struct *vma = vmf->vma;
     gfp_t gfp;
     struct folio *folio;
     unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
 
     if (!transhuge_vma_suitable(vma, haddr))
         return VM_FAULT_FALLBACK;
     if (unlikely(anon_vma_prepare(vma)))
         return VM_FAULT_OOM;
     khugepaged_enter_vma(vma, vma->vm_flags);
 
     if (!(vmf->flags & FAULT_FLAG_WRITE) &&
             !mm_forbids_zeropage(vma->vm_mm) &&
             transparent_hugepage_use_zero_page()) {
         pgtable_t pgtable;
         struct page *zero_page;
         vm_fault_t ret;
         pgtable = pte_alloc_one(vma->vm_mm);
         if (unlikely(!pgtable))
             return VM_FAULT_OOM;
         zero_page = mm_get_huge_zero_page(vma->vm_mm);
         if (unlikely(!zero_page)) {
             pte_free(vma->vm_mm, pgtable);
             count_vm_event(THP_FAULT_FALLBACK);
             return VM_FAULT_FALLBACK;
         }
         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
         ret = 0;
         if (pmd_none(*vmf->pmd)) {
             ret = check_stable_address_space(vma->vm_mm);
             if (ret) {
                 spin_unlock(vmf->ptl);
                 pte_free(vma->vm_mm, pgtable);
             } else if (userfaultfd_missing(vma)) {
                 spin_unlock(vmf->ptl);
                 pte_free(vma->vm_mm, pgtable);
                 ret = handle_userfault(vmf, VM_UFFD_MISSING);
                 VM_BUG_ON(ret & VM_FAULT_FALLBACK);
             } else {
                 set_huge_zero_page(pgtable, vma->vm_mm, vma,
                            haddr, vmf->pmd, zero_page);
                 update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
                 spin_unlock(vmf->ptl);
             }
         } else {
             spin_unlock(vmf->ptl);
             pte_free(vma->vm_mm, pgtable);
         }
         return ret;
     }
     gfp = vma_thp_gfp_mask(vma);
     folio = vma_alloc_folio(gfp, HPAGE_PMD_ORDER, vma, haddr, true);
     if (unlikely(!folio)) {
         count_vm_event(THP_FAULT_FALLBACK);
         return VM_FAULT_FALLBACK;
     }
     return __do_huge_pmd_anonymous_page(vmf, &folio->page, gfp);
 }
 
 static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
         pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write,
         pgtable_t pgtable)
 {
     struct mm_struct *mm = vma->vm_mm;
     pmd_t entry;
     spinlock_t *ptl;
 
     ptl = pmd_lock(mm, pmd);
     if (!pmd_none(*pmd)) {
         if (write) {
             if (pmd_pfn(*pmd) != pfn_t_to_pfn(pfn)) {
                 WARN_ON_ONCE(!is_huge_zero_pmd(*pmd));
                 goto out_unlock;
             }
             entry = pmd_mkyoung(*pmd);
             entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
             if (pmdp_set_access_flags(vma, addr, pmd, entry, 1))
                 update_mmu_cache_pmd(vma, addr, pmd);
         }
 
         goto out_unlock;
     }
 
     entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
     if (pfn_t_devmap(pfn))
         entry = pmd_mkdevmap(entry);
     if (write) {
         entry = pmd_mkyoung(pmd_mkdirty(entry));
         entry = maybe_pmd_mkwrite(entry, vma);
     }
 
     if (pgtable) {
         pgtable_trans_huge_deposit(mm, pmd, pgtable);
         mm_inc_nr_ptes(mm);
         pgtable = NULL;
     }
 
     set_pmd_at(mm, addr, pmd, entry);
     update_mmu_cache_pmd(vma, addr, pmd);
 
 out_unlock:
     spin_unlock(ptl);
     if (pgtable)
         pte_free(mm, pgtable);
 }
 
 /**
  * vmf_insert_pfn_pmd_prot - insert a pmd size pfn
  * @vmf: Structure describing the fault
  * @pfn: pfn to insert
  * @pgprot: page protection to use
  * @write: whether it's a write fault
  *
  * Insert a pmd size pfn. See vmf_insert_pfn() for additional info and
  * also consult the vmf_insert_mixed_prot() documentation when
  * @pgprot != @vmf->vma->vm_page_prot.
  *
  * Return: vm_fault_t value.
  */
 vm_fault_t vmf_insert_pfn_pmd_prot(struct vm_fault *vmf, pfn_t pfn,
                    pgprot_t pgprot, bool write)
 {
     unsigned long addr = vmf->address & PMD_MASK;
     struct vm_area_struct *vma = vmf->vma;
     pgtable_t pgtable = NULL;
 
     /*
      * If we had pmd_special, we could avoid all these restrictions,
      * but we need to be consistent with PTEs and architectures that
      * can't support a 'special' bit.
      */
     BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
             !pfn_t_devmap(pfn));
     BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
                         (VM_PFNMAP|VM_MIXEDMAP));
     BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
 
     if (addr < vma->vm_start || addr >= vma->vm_end)
         return VM_FAULT_SIGBUS;
 
     if (arch_needs_pgtable_deposit()) {
         pgtable = pte_alloc_one(vma->vm_mm);
         if (!pgtable)
             return VM_FAULT_OOM;
     }
 
     track_pfn_insert(vma, &pgprot, pfn);
 
     insert_pfn_pmd(vma, addr, vmf->pmd, pfn, pgprot, write, pgtable);
     return VM_FAULT_NOPAGE;
 }
 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd_prot);
 
 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 static pud_t maybe_pud_mkwrite(pud_t pud, struct vm_area_struct *vma)
 {
     if (likely(vma->vm_flags & VM_WRITE))
         pud = pud_mkwrite(pud);
     return pud;
 }
 
 static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
         pud_t *pud, pfn_t pfn, pgprot_t prot, bool write)
 {
     struct mm_struct *mm = vma->vm_mm;
     pud_t entry;
     spinlock_t *ptl;
 
     ptl = pud_lock(mm, pud);
     if (!pud_none(*pud)) {
         if (write) {
             if (pud_pfn(*pud) != pfn_t_to_pfn(pfn)) {
                 WARN_ON_ONCE(!is_huge_zero_pud(*pud));
                 goto out_unlock;
             }
             entry = pud_mkyoung(*pud);
             entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma);
             if (pudp_set_access_flags(vma, addr, pud, entry, 1))
                 update_mmu_cache_pud(vma, addr, pud);
         }
         goto out_unlock;
     }
 
     entry = pud_mkhuge(pfn_t_pud(pfn, prot));
     if (pfn_t_devmap(pfn))
         entry = pud_mkdevmap(entry);
     if (write) {
         entry = pud_mkyoung(pud_mkdirty(entry));
         entry = maybe_pud_mkwrite(entry, vma);
     }
     set_pud_at(mm, addr, pud, entry);
     update_mmu_cache_pud(vma, addr, pud);
 
 out_unlock:
     spin_unlock(ptl);
 }
 
 /**
  * vmf_insert_pfn_pud_prot - insert a pud size pfn
  * @vmf: Structure describing the fault
  * @pfn: pfn to insert
  * @pgprot: page protection to use
  * @write: whether it's a write fault
  *
  * Insert a pud size pfn. See vmf_insert_pfn() for additional info and
  * also consult the vmf_insert_mixed_prot() documentation when
  * @pgprot != @vmf->vma->vm_page_prot.
  *
  * Return: vm_fault_t value.
  */
 vm_fault_t vmf_insert_pfn_pud_prot(struct vm_fault *vmf, pfn_t pfn,
                    pgprot_t pgprot, bool write)
 {
     unsigned long addr = vmf->address & PUD_MASK;
     struct vm_area_struct *vma = vmf->vma;
 
     /*
      * If we had pud_special, we could avoid all these restrictions,
      * but we need to be consistent with PTEs and architectures that
      * can't support a 'special' bit.
      */
     BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
             !pfn_t_devmap(pfn));
     BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
                         (VM_PFNMAP|VM_MIXEDMAP));
     BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
 
     if (addr < vma->vm_start || addr >= vma->vm_end)
         return VM_FAULT_SIGBUS;
 
     track_pfn_insert(vma, &pgprot, pfn);
 
     insert_pfn_pud(vma, addr, vmf->pud, pfn, pgprot, write);
     return VM_FAULT_NOPAGE;
 }
 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pud_prot);
 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
 
 static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
               pmd_t *pmd, bool write)
 {
     pmd_t _pmd;
 
     _pmd = pmd_mkyoung(*pmd);
     if (write)
         _pmd = pmd_mkdirty(_pmd);
     if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
                   pmd, _pmd, write))
         update_mmu_cache_pmd(vma, addr, pmd);
 }
 
 struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
         pmd_t *pmd, int flags, struct dev_pagemap **pgmap)
 {
     unsigned long pfn = pmd_pfn(*pmd);
     struct mm_struct *mm = vma->vm_mm;
     struct page *page;
 
     assert_spin_locked(pmd_lockptr(mm, pmd));
 
     /* FOLL_GET and FOLL_PIN are mutually exclusive. */
     if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
              (FOLL_PIN | FOLL_GET)))
         return NULL;
 
     if (flags & FOLL_WRITE && !pmd_write(*pmd))
         return NULL;
 
     if (pmd_present(*pmd) && pmd_devmap(*pmd))
         /* pass */;
     else
         return NULL;
 
     if (flags & FOLL_TOUCH)
         touch_pmd(vma, addr, pmd, flags & FOLL_WRITE);
 
     /*
      * device mapped pages can only be returned if the
      * caller will manage the page reference count.
      */
     if (!(flags & (FOLL_GET | FOLL_PIN)))
         return ERR_PTR(-EEXIST);
 
     pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
     *pgmap = get_dev_pagemap(pfn, *pgmap);
     if (!*pgmap)
         return ERR_PTR(-EFAULT);
     page = pfn_to_page(pfn);
     if (!try_grab_page(page, flags))
         page = ERR_PTR(-ENOMEM);
 
     return page;
 }
 
 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
           pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
           struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
 {
     spinlock_t *dst_ptl, *src_ptl;
     struct page *src_page;
     pmd_t pmd;
     pgtable_t pgtable = NULL;
     int ret = -ENOMEM;
 
     /* Skip if can be re-fill on fault */
     if (!vma_is_anonymous(dst_vma))
         return 0;
 
     pgtable = pte_alloc_one(dst_mm);
     if (unlikely(!pgtable))
         goto out;
 
     dst_ptl = pmd_lock(dst_mm, dst_pmd);
     src_ptl = pmd_lockptr(src_mm, src_pmd);
     spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
 
     ret = -EAGAIN;
     pmd = *src_pmd;
 
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
     if (unlikely(is_swap_pmd(pmd))) {
         swp_entry_t entry = pmd_to_swp_entry(pmd);
 
         VM_BUG_ON(!is_pmd_migration_entry(pmd));
         if (!is_readable_migration_entry(entry)) {
             entry = make_readable_migration_entry(
                             swp_offset(entry));
             pmd = swp_entry_to_pmd(entry);
             if (pmd_swp_soft_dirty(*src_pmd))
                 pmd = pmd_swp_mksoft_dirty(pmd);
             if (pmd_swp_uffd_wp(*src_pmd))
                 pmd = pmd_swp_mkuffd_wp(pmd);
             set_pmd_at(src_mm, addr, src_pmd, pmd);
         }
         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
         mm_inc_nr_ptes(dst_mm);
         pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
         if (!userfaultfd_wp(dst_vma))
             pmd = pmd_swp_clear_uffd_wp(pmd);
         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
         ret = 0;
         goto out_unlock;
     }
 #endif
 
     if (unlikely(!pmd_trans_huge(pmd))) {
         pte_free(dst_mm, pgtable);
         goto out_unlock;
     }
     /*
      * When page table lock is held, the huge zero pmd should not be
      * under splitting since we don't split the page itself, only pmd to
      * a page table.
      */
     if (is_huge_zero_pmd(pmd)) {
         /*
          * get_huge_zero_page() will never allocate a new page here,
          * since we already have a zero page to copy. It just takes a
          * reference.
          */
         mm_get_huge_zero_page(dst_mm);
         goto out_zero_page;
     }
 
     src_page = pmd_page(pmd);
     VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
 
     get_page(src_page);
     if (unlikely(page_try_dup_anon_rmap(src_page, true, src_vma))) {
         /* Page maybe pinned: split and retry the fault on PTEs. */
         put_page(src_page);
         pte_free(dst_mm, pgtable);
         spin_unlock(src_ptl);
         spin_unlock(dst_ptl);
         __split_huge_pmd(src_vma, src_pmd, addr, false, NULL);
         return -EAGAIN;
     }
     add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 out_zero_page:
     mm_inc_nr_ptes(dst_mm);
     pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
     pmdp_set_wrprotect(src_mm, addr, src_pmd);
     if (!userfaultfd_wp(dst_vma))
         pmd = pmd_clear_uffd_wp(pmd);
     pmd = pmd_mkold(pmd_wrprotect(pmd));
     set_pmd_at(dst_mm, addr, dst_pmd, pmd);
 
     ret = 0;
 out_unlock:
     spin_unlock(src_ptl);
     spin_unlock(dst_ptl);
 out:
     return ret;
 }
 
 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 static void touch_pud(struct vm_area_struct *vma, unsigned long addr,
               pud_t *pud, bool write)
 {
     pud_t _pud;
 
     _pud = pud_mkyoung(*pud);
     if (write)
         _pud = pud_mkdirty(_pud);
     if (pudp_set_access_flags(vma, addr & HPAGE_PUD_MASK,
                   pud, _pud, write))
         update_mmu_cache_pud(vma, addr, pud);
 }
 
 struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
         pud_t *pud, int flags, struct dev_pagemap **pgmap)
 {
     unsigned long pfn = pud_pfn(*pud);
     struct mm_struct *mm = vma->vm_mm;
     struct page *page;
 
     assert_spin_locked(pud_lockptr(mm, pud));
 
     if (flags & FOLL_WRITE && !pud_write(*pud))
         return NULL;
 
     /* FOLL_GET and FOLL_PIN are mutually exclusive. */
     if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
              (FOLL_PIN | FOLL_GET)))
         return NULL;
 
     if (pud_present(*pud) && pud_devmap(*pud))
         /* pass */;
     else
         return NULL;
 
     if (flags & FOLL_TOUCH)
         touch_pud(vma, addr, pud, flags & FOLL_WRITE);
 
     /*
      * device mapped pages can only be returned if the
      * caller will manage the page reference count.
      *
      * At least one of FOLL_GET | FOLL_PIN must be set, so assert that here:
      */
     if (!(flags & (FOLL_GET | FOLL_PIN)))
         return ERR_PTR(-EEXIST);
 
     pfn += (addr & ~PUD_MASK) >> PAGE_SHIFT;
     *pgmap = get_dev_pagemap(pfn, *pgmap);
     if (!*pgmap)
         return ERR_PTR(-EFAULT);
     page = pfn_to_page(pfn);
     if (!try_grab_page(page, flags))
         page = ERR_PTR(-ENOMEM);
 
     return page;
 }
 
 int copy_huge_pud(struct mm_struct *dst_mm, struct mm_struct *src_mm,
           pud_t *dst_pud, pud_t *src_pud, unsigned long addr,
           struct vm_area_struct *vma)
 {
     spinlock_t *dst_ptl, *src_ptl;
     pud_t pud;
     int ret;
 
     dst_ptl = pud_lock(dst_mm, dst_pud);
     src_ptl = pud_lockptr(src_mm, src_pud);
     spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
 
     ret = -EAGAIN;
     pud = *src_pud;
     if (unlikely(!pud_trans_huge(pud) && !pud_devmap(pud)))
         goto out_unlock;
 
     /*
      * When page table lock is held, the huge zero pud should not be
      * under splitting since we don't split the page itself, only pud to
      * a page table.
      */
     if (is_huge_zero_pud(pud)) {
         /* No huge zero pud yet */
     }
 
     /*
      * TODO: once we support anonymous pages, use page_try_dup_anon_rmap()
      * and split if duplicating fails.
      */
     pudp_set_wrprotect(src_mm, addr, src_pud);
     pud = pud_mkold(pud_wrprotect(pud));
     set_pud_at(dst_mm, addr, dst_pud, pud);
 
     ret = 0;
 out_unlock:
     spin_unlock(src_ptl);
     spin_unlock(dst_ptl);
     return ret;
 }
 
 void huge_pud_set_accessed(struct vm_fault *vmf, pud_t orig_pud)
 {
     bool write = vmf->flags & FAULT_FLAG_WRITE;
 
     vmf->ptl = pud_lock(vmf->vma->vm_mm, vmf->pud);
     if (unlikely(!pud_same(*vmf->pud, orig_pud)))
         goto unlock;
 
     touch_pud(vmf->vma, vmf->address, vmf->pud, write);
 unlock:
     spin_unlock(vmf->ptl);
 }
 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
 
 void huge_pmd_set_accessed(struct vm_fault *vmf)
 {
     bool write = vmf->flags & FAULT_FLAG_WRITE;
 
     vmf->ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
     if (unlikely(!pmd_same(*vmf->pmd, vmf->orig_pmd)))
         goto unlock;
 
     touch_pmd(vmf->vma, vmf->address, vmf->pmd, write);
 
 unlock:
     spin_unlock(vmf->ptl);
 }
 
 vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf)
 {
     const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
     struct vm_area_struct *vma = vmf->vma;
     struct page *page;
     unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
     pmd_t orig_pmd = vmf->orig_pmd;
 
     vmf->ptl = pmd_lockptr(vma->vm_mm, vmf->pmd);
     VM_BUG_ON_VMA(!vma->anon_vma, vma);
 
     VM_BUG_ON(unshare && (vmf->flags & FAULT_FLAG_WRITE));
     VM_BUG_ON(!unshare && !(vmf->flags & FAULT_FLAG_WRITE));
 
     if (is_huge_zero_pmd(orig_pmd))
         goto fallback;
 
     spin_lock(vmf->ptl);
 
     if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) {
         spin_unlock(vmf->ptl);
         return 0;
     }
 
     page = pmd_page(orig_pmd);
     VM_BUG_ON_PAGE(!PageHead(page), page);
 
     /* Early check when only holding the PT lock. */
     if (PageAnonExclusive(page))
         goto reuse;
 
     if (!trylock_page(page)) {
         get_page(page);
         spin_unlock(vmf->ptl);
         lock_page(page);
         spin_lock(vmf->ptl);
         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) {
             spin_unlock(vmf->ptl);
             unlock_page(page);
             put_page(page);
             return 0;
         }
         put_page(page);
     }
 
     /* Recheck after temporarily dropping the PT lock. */
     if (PageAnonExclusive(page)) {
         unlock_page(page);
         goto reuse;
     }
 
     /*
      * See do_wp_page(): we can only reuse the page exclusively if there are
      * no additional references. Note that we always drain the LRU
      * pagevecs immediately after adding a THP.
      */
     if (page_count(page) > 1 + PageSwapCache(page) * thp_nr_pages(page))
         goto unlock_fallback;
     if (PageSwapCache(page))
         try_to_free_swap(page);
     if (page_count(page) == 1) {
         pmd_t entry;
 
         page_move_anon_rmap(page, vma);
         unlock_page(page);
 reuse:
         if (unlikely(unshare)) {
             spin_unlock(vmf->ptl);
             return 0;
         }
         entry = pmd_mkyoung(orig_pmd);
         entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
         if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry, 1))
             update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
         spin_unlock(vmf->ptl);
         return VM_FAULT_WRITE;
     }
 
 unlock_fallback:
     unlock_page(page);
     spin_unlock(vmf->ptl);
 fallback:
     __split_huge_pmd(vma, vmf->pmd, vmf->address, false, NULL);
     return VM_FAULT_FALLBACK;
 }
 
 /* FOLL_FORCE can write to even unwritable PMDs in COW mappings. */
 static inline bool can_follow_write_pmd(pmd_t pmd, struct page *page,
                     struct vm_area_struct *vma,
                     unsigned int flags)
 {
     /* If the pmd is writable, we can write to the page. */
     if (pmd_write(pmd))
         return true;
 
     /* Maybe FOLL_FORCE is set to override it? */
     if (!(flags & FOLL_FORCE))
         return false;
 
     /* But FOLL_FORCE has no effect on shared mappings */
     if (vma->vm_flags & (VM_MAYSHARE | VM_SHARED))
         return false;
 
     /* ... or read-only private ones */
     if (!(vma->vm_flags & VM_MAYWRITE))
         return false;
 
     /* ... or already writable ones that just need to take a write fault */
     if (vma->vm_flags & VM_WRITE)
         return false;
 
     /*
      * See can_change_pte_writable(): we broke COW and could map the page
      * writable if we have an exclusive anonymous page ...
      */
     if (!page || !PageAnon(page) || !PageAnonExclusive(page))
         return false;
 
     /* ... and a write-fault isn't required for other reasons. */
     if (vma_soft_dirty_enabled(vma) && !pmd_soft_dirty(pmd))
         return false;
     return !userfaultfd_huge_pmd_wp(vma, pmd);
 }
 
 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
                    unsigned long addr,
                    pmd_t *pmd,
                    unsigned int flags)
 {
     struct mm_struct *mm = vma->vm_mm;
     struct page *page;
 
     assert_spin_locked(pmd_lockptr(mm, pmd));
 
     page = pmd_page(*pmd);
     VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
 
     if ((flags & FOLL_WRITE) &&
         !can_follow_write_pmd(*pmd, page, vma, flags))
         return NULL;
 
     /* Avoid dumping huge zero page */
     if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
         return ERR_PTR(-EFAULT);
 
     /* Full NUMA hinting faults to serialise migration in fault paths */
     if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
         return NULL;
 
     if (!pmd_write(*pmd) && gup_must_unshare(flags, page))
         return ERR_PTR(-EMLINK);
 
     VM_BUG_ON_PAGE((flags & FOLL_PIN) && PageAnon(page) &&
             !PageAnonExclusive(page), page);
 
     if (!try_grab_page(page, flags))
         return ERR_PTR(-ENOMEM);
 
     if (flags & FOLL_TOUCH)
         touch_pmd(vma, addr, pmd, flags & FOLL_WRITE);
 
     page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
     VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
 
     return page;
 }
 
 /* NUMA hinting page fault entry point for trans huge pmds */
 vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
 {
     struct vm_area_struct *vma = vmf->vma;
     pmd_t oldpmd = vmf->orig_pmd;
     pmd_t pmd;
     struct page *page;
     unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
     int page_nid = NUMA_NO_NODE;
     int target_nid, last_cpupid = -1;
     bool migrated = false;
     bool was_writable = pmd_savedwrite(oldpmd);
     int flags = 0;
 
     vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
     if (unlikely(!pmd_same(oldpmd, *vmf->pmd))) {
         spin_unlock(vmf->ptl);
         goto out;
     }
 
     pmd = pmd_modify(oldpmd, vma->vm_page_prot);
     page = vm_normal_page_pmd(vma, haddr, pmd);
     if (!page)
         goto out_map;
 
     /* See similar comment in do_numa_page for explanation */
     if (!was_writable)
         flags |= TNF_NO_GROUP;
 
     page_nid = page_to_nid(page);
     last_cpupid = page_cpupid_last(page);
     target_nid = numa_migrate_prep(page, vma, haddr, page_nid,
                        &flags);
 
     if (target_nid == NUMA_NO_NODE) {
         put_page(page);
         goto out_map;
     }
 
     spin_unlock(vmf->ptl);
 
     migrated = migrate_misplaced_page(page, vma, target_nid);
     if (migrated) {
         flags |= TNF_MIGRATED;
         page_nid = target_nid;
     } else {
         flags |= TNF_MIGRATE_FAIL;
         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
         if (unlikely(!pmd_same(oldpmd, *vmf->pmd))) {
             spin_unlock(vmf->ptl);
             goto out;
         }
         goto out_map;
     }
 
 out:
     if (page_nid != NUMA_NO_NODE)
         task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR,
                 flags);
 
     return 0;
 
 out_map:
     /* Restore the PMD */
     pmd = pmd_modify(oldpmd, vma->vm_page_prot);
     pmd = pmd_mkyoung(pmd);
     if (was_writable)
         pmd = pmd_mkwrite(pmd);
     set_pmd_at(vma->vm_mm, haddr, vmf->pmd, pmd);
     update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
     spin_unlock(vmf->ptl);
     goto out;
 }
 
 /*
  * Return true if we do MADV_FREE successfully on entire pmd page.
  * Otherwise, return false.
  */
 bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
         pmd_t *pmd, unsigned long addr, unsigned long next)
 {
     spinlock_t *ptl;
     pmd_t orig_pmd;
     struct page *page;
     struct mm_struct *mm = tlb->mm;
     bool ret = false;
 
     tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
 
     ptl = pmd_trans_huge_lock(pmd, vma);
     if (!ptl)
         goto out_unlocked;
 
     orig_pmd = *pmd;
     if (is_huge_zero_pmd(orig_pmd))
         goto out;
 
     if (unlikely(!pmd_present(orig_pmd))) {
         VM_BUG_ON(thp_migration_supported() &&
                   !is_pmd_migration_entry(orig_pmd));
         goto out;
     }
 
     page = pmd_page(orig_pmd);
     /*
      * If other processes are mapping this page, we couldn't discard
      * the page unless they all do MADV_FREE so let's skip the page.
      */
     if (total_mapcount(page) != 1)
         goto out;
 
     if (!trylock_page(page))
         goto out;
 
     /*
      * If user want to discard part-pages of THP, split it so MADV_FREE
      * will deactivate only them.
      */
     if (next - addr != HPAGE_PMD_SIZE) {
         get_page(page);
         spin_unlock(ptl);
         split_huge_page(page);
         unlock_page(page);
         put_page(page);
         goto out_unlocked;
     }
 
     if (PageDirty(page))
         ClearPageDirty(page);
     unlock_page(page);
 
     if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
         pmdp_invalidate(vma, addr, pmd);
         orig_pmd = pmd_mkold(orig_pmd);
         orig_pmd = pmd_mkclean(orig_pmd);
 
         set_pmd_at(mm, addr, pmd, orig_pmd);
         tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
     }
 
     mark_page_lazyfree(page);
     ret = true;
 out:
     spin_unlock(ptl);
 out_unlocked:
     return ret;
 }
 
 static inline void zap_deposited_table(struct mm_struct *mm, pmd_t *pmd)
 {
     pgtable_t pgtable;
 
     pgtable = pgtable_trans_huge_withdraw(mm, pmd);
     pte_free(mm, pgtable);
     mm_dec_nr_ptes(mm);
 }
 
 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
          pmd_t *pmd, unsigned long addr)
 {
     pmd_t orig_pmd;
     spinlock_t *ptl;
 
     tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
 
     ptl = __pmd_trans_huge_lock(pmd, vma);
     if (!ptl)
         return 0;
     /*
      * For architectures like ppc64 we look at deposited pgtable
      * when calling pmdp_huge_get_and_clear. So do the
      * pgtable_trans_huge_withdraw after finishing pmdp related
      * operations.
      */
     orig_pmd = pmdp_huge_get_and_clear_full(vma, addr, pmd,
                         tlb->fullmm);
     tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
     if (vma_is_special_huge(vma)) {
         if (arch_needs_pgtable_deposit())
             zap_deposited_table(tlb->mm, pmd);
         spin_unlock(ptl);
     } else if (is_huge_zero_pmd(orig_pmd)) {
         zap_deposited_table(tlb->mm, pmd);
         spin_unlock(ptl);
     } else {
         struct page *page = NULL;
         int flush_needed = 1;
 
         if (pmd_present(orig_pmd)) {
             page = pmd_page(orig_pmd);
             page_remove_rmap(page, vma, true);
             VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
             VM_BUG_ON_PAGE(!PageHead(page), page);
         } else if (thp_migration_supported()) {
             swp_entry_t entry;
 
             VM_BUG_ON(!is_pmd_migration_entry(orig_pmd));
             entry = pmd_to_swp_entry(orig_pmd);
             page = pfn_swap_entry_to_page(entry);
             flush_needed = 0;
         } else
             WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
 
         if (PageAnon(page)) {
             zap_deposited_table(tlb->mm, pmd);
             add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
         } else {
             if (arch_needs_pgtable_deposit())
                 zap_deposited_table(tlb->mm, pmd);
             add_mm_counter(tlb->mm, mm_counter_file(page), -HPAGE_PMD_NR);
         }
 
         spin_unlock(ptl);
         if (flush_needed)
             tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE);
     }
     return 1;
 }
 
 #ifndef pmd_move_must_withdraw
 static inline int pmd_move_must_withdraw(spinlock_t *new_pmd_ptl,
                      spinlock_t *old_pmd_ptl,
                      struct vm_area_struct *vma)
 {
     /*
      * With split pmd lock we also need to move preallocated
      * PTE page table if new_pmd is on different PMD page table.
      *
      * We also don't deposit and withdraw tables for file pages.
      */
     return (new_pmd_ptl != old_pmd_ptl) && vma_is_anonymous(vma);
 }
 #endif
 
 static pmd_t move_soft_dirty_pmd(pmd_t pmd)
 {
 #ifdef CONFIG_MEM_SOFT_DIRTY
     if (unlikely(is_pmd_migration_entry(pmd)))
         pmd = pmd_swp_mksoft_dirty(pmd);
     else if (pmd_present(pmd))
         pmd = pmd_mksoft_dirty(pmd);
 #endif
     return pmd;
 }
 
 bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
           unsigned long new_addr, pmd_t *old_pmd, pmd_t *new_pmd)
 {
     spinlock_t *old_ptl, *new_ptl;
     pmd_t pmd;
     struct mm_struct *mm = vma->vm_mm;
     bool force_flush = false;
 
     /*
      * The destination pmd shouldn't be established, free_pgtables()
      * should have release it.
      */
     if (WARN_ON(!pmd_none(*new_pmd))) {
         VM_BUG_ON(pmd_trans_huge(*new_pmd));
         return false;
     }
 
     /*
      * We don't have to worry about the ordering of src and dst
      * ptlocks because exclusive mmap_lock prevents deadlock.
      */
     old_ptl = __pmd_trans_huge_lock(old_pmd, vma);
     if (old_ptl) {
         new_ptl = pmd_lockptr(mm, new_pmd);
         if (new_ptl != old_ptl)
             spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
         pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
         if (pmd_present(pmd))
             force_flush = true;
         VM_BUG_ON(!pmd_none(*new_pmd));
 
         if (pmd_move_must_withdraw(new_ptl, old_ptl, vma)) {
             pgtable_t pgtable;
             pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
             pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
         }
         pmd = move_soft_dirty_pmd(pmd);
         set_pmd_at(mm, new_addr, new_pmd, pmd);
         if (force_flush)
             flush_pmd_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
         if (new_ptl != old_ptl)
             spin_unlock(new_ptl);
         spin_unlock(old_ptl);
         return true;
     }
     return false;
 }
 
 /*
  * Returns
  *  - 0 if PMD could not be locked
  *  - 1 if PMD was locked but protections unchanged and TLB flush unnecessary
  *      or if prot_numa but THP migration is not supported
  *  - HPAGE_PMD_NR if protections changed and TLB flush necessary
  */
 int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
             pmd_t *pmd, unsigned long addr, pgprot_t newprot,
             unsigned long cp_flags)
 {
     struct mm_struct *mm = vma->vm_mm;
     spinlock_t *ptl;
     pmd_t oldpmd, entry;
     bool preserve_write;
     int ret;
     bool prot_numa = cp_flags & MM_CP_PROT_NUMA;
     bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
     bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;
 
     tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
 
     if (prot_numa && !thp_migration_supported())
         return 1;
 
     ptl = __pmd_trans_huge_lock(pmd, vma);
     if (!ptl)
         return 0;
 
     preserve_write = prot_numa && pmd_write(*pmd);
     ret = 1;
 
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
     if (is_swap_pmd(*pmd)) {
         swp_entry_t entry = pmd_to_swp_entry(*pmd);
         struct page *page = pfn_swap_entry_to_page(entry);
 
         VM_BUG_ON(!is_pmd_migration_entry(*pmd));
         if (is_writable_migration_entry(entry)) {
             pmd_t newpmd;
             /*
              * A protection check is difficult so
              * just be safe and disable write
              */
             if (PageAnon(page))
                 entry = make_readable_exclusive_migration_entry(swp_offset(entry));
             else
                 entry = make_readable_migration_entry(swp_offset(entry));
             newpmd = swp_entry_to_pmd(entry);
             if (pmd_swp_soft_dirty(*pmd))
                 newpmd = pmd_swp_mksoft_dirty(newpmd);
             if (pmd_swp_uffd_wp(*pmd))
                 newpmd = pmd_swp_mkuffd_wp(newpmd);
             set_pmd_at(mm, addr, pmd, newpmd);
         }
         goto unlock;
     }
 #endif
 
     if (prot_numa) {
         struct page *page;
         /*
          * Avoid trapping faults against the zero page. The read-only
          * data is likely to be read-cached on the local CPU and
          * local/remote hits to the zero page are not interesting.
          */
         if (is_huge_zero_pmd(*pmd))
             goto unlock;
 
         if (pmd_protnone(*pmd))
             goto unlock;
 
         page = pmd_page(*pmd);
         /*
          * Skip scanning top tier node if normal numa
          * balancing is disabled
          */
         if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
             node_is_toptier(page_to_nid(page)))
             goto unlock;
     }
     /*
      * In case prot_numa, we are under mmap_read_lock(mm). It's critical
      * to not clear pmd intermittently to avoid race with MADV_DONTNEED
      * which is also under mmap_read_lock(mm):
      *
      *  CPU0:               CPU1:
      *              change_huge_pmd(prot_numa=1)
      *               pmdp_huge_get_and_clear_notify()
      * madvise_dontneed()
      *  zap_pmd_range()
      *   pmd_trans_huge(*pmd) == 0 (without ptl)
      *   // skip the pmd
      *               set_pmd_at();
      *               // pmd is re-established
      *
      * The race makes MADV_DONTNEED miss the huge pmd and don't clear it
      * which may break userspace.
      *
      * pmdp_invalidate_ad() is required to make sure we don't miss
      * dirty/young flags set by hardware.
      */
     oldpmd = pmdp_invalidate_ad(vma, addr, pmd);
 
     entry = pmd_modify(oldpmd, newprot);
     if (preserve_write)
         entry = pmd_mk_savedwrite(entry);
     if (uffd_wp) {
         entry = pmd_wrprotect(entry);
         entry = pmd_mkuffd_wp(entry);
     } else if (uffd_wp_resolve) {
         /*
          * Leave the write bit to be handled by PF interrupt
          * handler, then things like COW could be properly
          * handled.
          */
         entry = pmd_clear_uffd_wp(entry);
     }
     ret = HPAGE_PMD_NR;
     set_pmd_at(mm, addr, pmd, entry);
 
     if (huge_pmd_needs_flush(oldpmd, entry))
         tlb_flush_pmd_range(tlb, addr, HPAGE_PMD_SIZE);
 
     BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
 unlock:
     spin_unlock(ptl);
     return ret;
 }
 
 /*
  * Returns page table lock pointer if a given pmd maps a thp, NULL otherwise.
  *
  * Note that if it returns page table lock pointer, this routine returns without
  * unlocking page table lock. So callers must unlock it.
  */
 spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
 {
     spinlock_t *ptl;
     ptl = pmd_lock(vma->vm_mm, pmd);
     if (likely(is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) ||
             pmd_devmap(*pmd)))
         return ptl;
     spin_unlock(ptl);
     return NULL;
 }
 
 /*
  * Returns page table lock pointer if a given pud maps a thp, NULL otherwise.
  *
  * Note that if it returns page table lock pointer, this routine returns without
  * unlocking page table lock. So callers must unlock it.
  */
 spinlock_t *__pud_trans_huge_lock(pud_t *pud, struct vm_area_struct *vma)
 {
     spinlock_t *ptl;
 
     ptl = pud_lock(vma->vm_mm, pud);
     if (likely(pud_trans_huge(*pud) || pud_devmap(*pud)))
         return ptl;
     spin_unlock(ptl);
     return NULL;
 }
 
 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
          pud_t *pud, unsigned long addr)
 {
     spinlock_t *ptl;
 
     ptl = __pud_trans_huge_lock(pud, vma);
     if (!ptl)
         return 0;
 
     pudp_huge_get_and_clear_full(tlb->mm, addr, pud, tlb->fullmm);
     tlb_remove_pud_tlb_entry(tlb, pud, addr);
     if (vma_is_special_huge(vma)) {
         spin_unlock(ptl);
         /* No zero page support yet */
     } else {
         /* No support for anonymous PUD pages yet */
         BUG();
     }
     return 1;
 }
 
 static void __split_huge_pud_locked(struct vm_area_struct *vma, pud_t *pud,
         unsigned long haddr)
 {
     VM_BUG_ON(haddr & ~HPAGE_PUD_MASK);
     VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
     VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PUD_SIZE, vma);
     VM_BUG_ON(!pud_trans_huge(*pud) && !pud_devmap(*pud));
 
     count_vm_event(THP_SPLIT_PUD);
 
     pudp_huge_clear_flush_notify(vma, haddr, pud);
 }
 
 void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud,
         unsigned long address)
 {
     spinlock_t *ptl;
     struct mmu_notifier_range range;
 
     mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
                 address & HPAGE_PUD_MASK,
                 (address & HPAGE_PUD_MASK) + HPAGE_PUD_SIZE);
     mmu_notifier_invalidate_range_start(&range);
     ptl = pud_lock(vma->vm_mm, pud);
     if (unlikely(!pud_trans_huge(*pud) && !pud_devmap(*pud)))
         goto out;
     __split_huge_pud_locked(vma, pud, range.start);
 
 out:
     spin_unlock(ptl);
     /*
      * No need to double call mmu_notifier->invalidate_range() callback as
      * the above pudp_huge_clear_flush_notify() did already call it.
      */
     mmu_notifier_invalidate_range_only_end(&range);
 }
 #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
 
 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
         unsigned long haddr, pmd_t *pmd)
 {
     struct mm_struct *mm = vma->vm_mm;
     pgtable_t pgtable;
     pmd_t _pmd;
     int i;
 
     /*
      * Leave pmd empty until pte is filled note that it is fine to delay
      * notification until mmu_notifier_invalidate_range_end() as we are
      * replacing a zero pmd write protected page with a zero pte write
      * protected page.
      *
      * See Documentation/mm/mmu_notifier.rst
      */
     pmdp_huge_clear_flush(vma, haddr, pmd);
 
     pgtable = pgtable_trans_huge_withdraw(mm, pmd);
     pmd_populate(mm, &_pmd, pgtable);
 
     for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
         pte_t *pte, entry;
         entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
         entry = pte_mkspecial(entry);
         pte = pte_offset_map(&_pmd, haddr);
         VM_BUG_ON(!pte_none(*pte));
         set_pte_at(mm, haddr, pte, entry);
         pte_unmap(pte);
     }
     smp_wmb(); /* make pte visible before pmd */
     pmd_populate(mm, pmd, pgtable);
 }
 
 static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
         unsigned long haddr, bool freeze)
 {
     struct mm_struct *mm = vma->vm_mm;
     struct page *page;
     pgtable_t pgtable;
     pmd_t old_pmd, _pmd;
     bool young, write, soft_dirty, pmd_migration = false, uffd_wp = false;
     bool anon_exclusive = false;
     unsigned long addr;
     int i;
 
     VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
     VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
     VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
     VM_BUG_ON(!is_pmd_migration_entry(*pmd) && !pmd_trans_huge(*pmd)
                 && !pmd_devmap(*pmd));
 
     count_vm_event(THP_SPLIT_PMD);
 
     if (!vma_is_anonymous(vma)) {
         old_pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
         /*
          * We are going to unmap this huge page. So
          * just go ahead and zap it
          */
         if (arch_needs_pgtable_deposit())
             zap_deposited_table(mm, pmd);
         if (vma_is_special_huge(vma))
             return;
         if (unlikely(is_pmd_migration_entry(old_pmd))) {
             swp_entry_t entry;
 
             entry = pmd_to_swp_entry(old_pmd);
             page = pfn_swap_entry_to_page(entry);
         } else {
             page = pmd_page(old_pmd);
             if (!PageDirty(page) && pmd_dirty(old_pmd))
                 set_page_dirty(page);
             if (!PageReferenced(page) && pmd_young(old_pmd))
                 SetPageReferenced(page);
             page_remove_rmap(page, vma, true);
             put_page(page);
         }
         add_mm_counter(mm, mm_counter_file(page), -HPAGE_PMD_NR);
         return;
     }
 
     if (is_huge_zero_pmd(*pmd)) {
         /*
          * FIXME: Do we want to invalidate secondary mmu by calling
          * mmu_notifier_invalidate_range() see comments below inside
          * __split_huge_pmd() ?
          *
          * We are going from a zero huge page write protected to zero
          * small page also write protected so it does not seems useful
          * to invalidate secondary mmu at this time.
          */
         return __split_huge_zero_page_pmd(vma, haddr, pmd);
     }
 
     /*
      * Up to this point the pmd is present and huge and userland has the
      * whole access to the hugepage during the split (which happens in
      * place). If we overwrite the pmd with the not-huge version pointing
      * to the pte here (which of course we could if all CPUs were bug
      * free), userland could trigger a small page size TLB miss on the
      * small sized TLB while the hugepage TLB entry is still established in
      * the huge TLB. Some CPU doesn't like that.
      * See http://support.amd.com/TechDocs/41322_10h_Rev_Gd.pdf, Erratum
      * 383 on page 105. Intel should be safe but is also warns that it's
      * only safe if the permission and cache attributes of the two entries
      * loaded in the two TLB is identical (which should be the case here).
      * But it is generally safer to never allow small and huge TLB entries
      * for the same virtual address to be loaded simultaneously. So instead
      * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the
      * current pmd notpresent (atomically because here the pmd_trans_huge
      * must remain set at all times on the pmd until the split is complete
      * for this pmd), then we flush the SMP TLB and finally we write the
      * non-huge version of the pmd entry with pmd_populate.
      */
     old_pmd = pmdp_invalidate(vma, haddr, pmd);
 
     pmd_migration = is_pmd_migration_entry(old_pmd);
     if (unlikely(pmd_migration)) {
         swp_entry_t entry;
 
         entry = pmd_to_swp_entry(old_pmd);
         page = pfn_swap_entry_to_page(entry);
         write = is_writable_migration_entry(entry);
         if (PageAnon(page))
             anon_exclusive = is_readable_exclusive_migration_entry(entry);
         young = false;
         soft_dirty = pmd_swp_soft_dirty(old_pmd);
         uffd_wp = pmd_swp_uffd_wp(old_pmd);
     } else {
         page = pmd_page(old_pmd);
         if (pmd_dirty(old_pmd))
             SetPageDirty(page);
         write = pmd_write(old_pmd);
         young = pmd_young(old_pmd);
         soft_dirty = pmd_soft_dirty(old_pmd);
         uffd_wp = pmd_uffd_wp(old_pmd);
 
         VM_BUG_ON_PAGE(!page_count(page), page);
         page_ref_add(page, HPAGE_PMD_NR - 1);
 
         /*
          * Without "freeze", we'll simply split the PMD, propagating the
          * PageAnonExclusive() flag for each PTE by setting it for
          * each subpage -- no need to (temporarily) clear.
          *
          * With "freeze" we want to replace mapped pages by
          * migration entries right away. This is only possible if we
          * managed to clear PageAnonExclusive() -- see
          * set_pmd_migration_entry().
          *
          * In case we cannot clear PageAnonExclusive(), split the PMD
          * only and let try_to_migrate_one() fail later.
          */
         anon_exclusive = PageAnon(page) && PageAnonExclusive(page);
         if (freeze && anon_exclusive && page_try_share_anon_rmap(page))
             freeze = false;
     }
 
     /*
      * Withdraw the table only after we mark the pmd entry invalid.
      * This's critical for some architectures (Power).
      */
     pgtable = pgtable_trans_huge_withdraw(mm, pmd);
     pmd_populate(mm, &_pmd, pgtable);
 
     for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
         pte_t entry, *pte;
         /*
          * Note that NUMA hinting access restrictions are not
          * transferred to avoid any possibility of altering
          * permissions across VMAs.
          */
         if (freeze || pmd_migration) {
             swp_entry_t swp_entry;
             if (write)
                 swp_entry = make_writable_migration_entry(
                             page_to_pfn(page + i));
             else if (anon_exclusive)
                 swp_entry = make_readable_exclusive_migration_entry(
                             page_to_pfn(page + i));
             else
                 swp_entry = make_readable_migration_entry(
                             page_to_pfn(page + i));
             entry = swp_entry_to_pte(swp_entry);
             if (soft_dirty)
                 entry = pte_swp_mksoft_dirty(entry);
             if (uffd_wp)
                 entry = pte_swp_mkuffd_wp(entry);
         } else {
             entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
             entry = maybe_mkwrite(entry, vma);
             if (anon_exclusive)
                 SetPageAnonExclusive(page + i);
             if (!write)
                 entry = pte_wrprotect(entry);
             if (!young)
                 entry = pte_mkold(entry);
             if (soft_dirty)
                 entry = pte_mksoft_dirty(entry);
             if (uffd_wp)
                 entry = pte_mkuffd_wp(entry);
         }
         pte = pte_offset_map(&_pmd, addr);
         BUG_ON(!pte_none(*pte));
         set_pte_at(mm, addr, pte, entry);
         if (!pmd_migration)
             atomic_inc(&page[i]._mapcount);
         pte_unmap(pte);
     }
 
     if (!pmd_migration) {
         /*
          * Set PG_double_map before dropping compound_mapcount to avoid
          * false-negative page_mapped().
          */
         if (compound_mapcount(page) > 1 &&
             !TestSetPageDoubleMap(page)) {
             for (i = 0; i < HPAGE_PMD_NR; i++)
                 atomic_inc(&page[i]._mapcount);
         }
 
         lock_page_memcg(page);
         if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
             /* Last compound_mapcount is gone. */
             __mod_lruvec_page_state(page, NR_ANON_THPS,
                         -HPAGE_PMD_NR);
             if (TestClearPageDoubleMap(page)) {
                 /* No need in mapcount reference anymore */
                 for (i = 0; i < HPAGE_PMD_NR; i++)
                     atomic_dec(&page[i]._mapcount);
             }
         }
         unlock_page_memcg(page);
 
         /* Above is effectively page_remove_rmap(page, vma, true) */
         munlock_vma_page(page, vma, true);
     }
 
     smp_wmb(); /* make pte visible before pmd */
     pmd_populate(mm, pmd, pgtable);
 
     if (freeze) {
         for (i = 0; i < HPAGE_PMD_NR; i++) {
             page_remove_rmap(page + i, vma, false);
             put_page(page + i);
         }
     }
 }
 
 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
         unsigned long address, bool freeze, struct folio *folio)
 {
     spinlock_t *ptl;
     struct mmu_notifier_range range;
 
     mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
                 address & HPAGE_PMD_MASK,
                 (address & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE);
     mmu_notifier_invalidate_range_start(&range);
     ptl = pmd_lock(vma->vm_mm, pmd);
 
     /*
      * If caller asks to setup a migration entry, we need a folio to check
      * pmd against. Otherwise we can end up replacing wrong folio.
      */
     VM_BUG_ON(freeze && !folio);
     VM_WARN_ON_ONCE(folio && !folio_test_locked(folio));
 
     if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) ||
         is_pmd_migration_entry(*pmd)) {
         /*
          * It's safe to call pmd_page when folio is set because it's
          * guaranteed that pmd is present.
          */
         if (folio && folio != page_folio(pmd_page(*pmd)))
             goto out;
         __split_huge_pmd_locked(vma, pmd, range.start, freeze);
     }
 
 out:
     spin_unlock(ptl);
     /*
      * No need to double call mmu_notifier->invalidate_range() callback.
      * They are 3 cases to consider inside __split_huge_pmd_locked():
      *  1) pmdp_huge_clear_flush_notify() call invalidate_range() obvious
      *  2) __split_huge_zero_page_pmd() read only zero page and any write
      *    fault will trigger a flush_notify before pointing to a new page
      *    (it is fine if the secondary mmu keeps pointing to the old zero
      *    page in the meantime)
      *  3) Split a huge pmd into pte pointing to the same page. No need
      *     to invalidate secondary tlb entry they are all still valid.
      *     any further changes to individual pte will notify. So no need
      *     to call mmu_notifier->invalidate_range()
      */
     mmu_notifier_invalidate_range_only_end(&range);
 }
 
 void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
         bool freeze, struct folio *folio)
 {
     pgd_t *pgd;
     p4d_t *p4d;
     pud_t *pud;
     pmd_t *pmd;
 
     pgd = pgd_offset(vma->vm_mm, address);
     if (!pgd_present(*pgd))
         return;
 
     p4d = p4d_offset(pgd, address);
     if (!p4d_present(*p4d))
         return;
 
     pud = pud_offset(p4d, address);
     if (!pud_present(*pud))
         return;
 
     pmd = pmd_offset(pud, address);
 
     __split_huge_pmd(vma, pmd, address, freeze, folio);
 }
 
 static inline void split_huge_pmd_if_needed(struct vm_area_struct *vma, unsigned long address)
 {
     /*
      * If the new address isn't hpage aligned and it could previously
      * contain an hugepage: check if we need to split an huge pmd.
      */
     if (!IS_ALIGNED(address, HPAGE_PMD_SIZE) &&
         range_in_vma(vma, ALIGN_DOWN(address, HPAGE_PMD_SIZE),
              ALIGN(address, HPAGE_PMD_SIZE)))
         split_huge_pmd_address(vma, address, false, NULL);
 }
 
 void vma_adjust_trans_huge(struct vm_area_struct *vma,
                  unsigned long start,
                  unsigned long end,
                  long adjust_next)
 {
     /* Check if we need to split start first. */
     split_huge_pmd_if_needed(vma, start);
 
     /* Check if we need to split end next. */
     split_huge_pmd_if_needed(vma, end);
 
     /*
      * If we're also updating the vma->vm_next->vm_start,
      * check if we need to split it.
      */
     if (adjust_next > 0) {
         struct vm_area_struct *next = vma->vm_next;
         unsigned long nstart = next->vm_start;
         nstart += adjust_next;
         split_huge_pmd_if_needed(next, nstart);
     }
 }
 
 static void unmap_page(struct page *page)
 {
     struct folio *folio = page_folio(page);
     enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD |
         TTU_SYNC;
 
     VM_BUG_ON_PAGE(!PageHead(page), page);
 
     /*
      * Anon pages need migration entries to preserve them, but file
      * pages can simply be left unmapped, then faulted back on demand.
      * If that is ever changed (perhaps for mlock), update remap_page().
      */
     if (folio_test_anon(folio))
         try_to_migrate(folio, ttu_flags);
     else
         try_to_unmap(folio, ttu_flags | TTU_IGNORE_MLOCK);
 }
 
 static void remap_page(struct folio *folio, unsigned long nr)
 {
     int i = 0;
 
     /* If unmap_page() uses try_to_migrate() on file, remove this check */
     if (!folio_test_anon(folio))
         return;
     for (;;) {
         remove_migration_ptes(folio, folio, true);
         i += folio_nr_pages(folio);
         if (i >= nr)
             break;
         folio = folio_next(folio);
     }
 }
 
 static void lru_add_page_tail(struct page *head, struct page *tail,
         struct lruvec *lruvec, struct list_head *list)
 {
     VM_BUG_ON_PAGE(!PageHead(head), head);
     VM_BUG_ON_PAGE(PageCompound(tail), head);
     VM_BUG_ON_PAGE(PageLRU(tail), head);
     lockdep_assert_held(&lruvec->lru_lock);
 
     if (list) {
         /* page reclaim is reclaiming a huge page */
         VM_WARN_ON(PageLRU(head));
         get_page(tail);
         list_add_tail(&tail->lru, list);
     } else {
         /* head is still on lru (and we have it frozen) */
         VM_WARN_ON(!PageLRU(head));
         if (PageUnevictable(tail))
             tail->mlock_count = 0;
         else
             list_add_tail(&tail->lru, &head->lru);
         SetPageLRU(tail);
     }
 }
 
 static void __split_huge_page_tail(struct page *head, int tail,
         struct lruvec *lruvec, struct list_head *list)
 {
     struct page *page_tail = head + tail;
 
     VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
 
     /*
      * Clone page flags before unfreezing refcount.
      *
      * After successful get_page_unless_zero() might follow flags change,
      * for example lock_page() which set PG_waiters.
      *
      * Note that for mapped sub-pages of an anonymous THP,
      * PG_anon_exclusive has been cleared in unmap_page() and is stored in
      * the migration entry instead from where remap_page() will restore it.
      * We can still have PG_anon_exclusive set on effectively unmapped and
      * unreferenced sub-pages of an anonymous THP: we can simply drop
      * PG_anon_exclusive (-> PG_mappedtodisk) for these here.
      */
     page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
     page_tail->flags |= (head->flags &
             ((1L << PG_referenced) |
              (1L << PG_swapbacked) |
              (1L << PG_swapcache) |
              (1L << PG_mlocked) |
              (1L << PG_uptodate) |
              (1L << PG_active) |
              (1L << PG_workingset) |
              (1L << PG_locked) |
              (1L << PG_unevictable) |
 #ifdef CONFIG_64BIT
              (1L << PG_arch_2) |
 #endif
              (1L << PG_dirty)));
 
     /* ->mapping in first tail page is compound_mapcount */
     VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
             page_tail);
     page_tail->mapping = head->mapping;
     page_tail->index = head->index + tail;
     page_tail->private = 0;
 
     /* Page flags must be visible before we make the page non-compound. */
     smp_wmb();
 
     /*
      * Clear PageTail before unfreezing page refcount.
      *
      * After successful get_page_unless_zero() might follow put_page()
      * which needs correct compound_head().
      */
     clear_compound_head(page_tail);
 
     /* Finally unfreeze refcount. Additional reference from page cache. */
     page_ref_unfreeze(page_tail, 1 + (!PageAnon(head) ||
                       PageSwapCache(head)));
 
     if (page_is_young(head))
         set_page_young(page_tail);
     if (page_is_idle(head))
         set_page_idle(page_tail);
 
     page_cpupid_xchg_last(page_tail, page_cpupid_last(head));
 
     /*
      * always add to the tail because some iterators expect new
      * pages to show after the currently processed elements - e.g.
      * migrate_pages
      */
     lru_add_page_tail(head, page_tail, lruvec, list);
 }
 
 static void __split_huge_page(struct page *page, struct list_head *list,
         pgoff_t end)
 {
     struct folio *folio = page_folio(page);
     struct page *head = &folio->page;
     struct lruvec *lruvec;
     struct address_space *swap_cache = NULL;
     unsigned long offset = 0;
     unsigned int nr = thp_nr_pages(head);
     int i;
 
     /* complete memcg works before add pages to LRU */
     split_page_memcg(head, nr);
 
     if (PageAnon(head) && PageSwapCache(head)) {
         swp_entry_t entry = { .val = page_private(head) };
 
         offset = swp_offset(entry);
         swap_cache = swap_address_space(entry);
         xa_lock(&swap_cache->i_pages);
     }
 
     /* lock lru list/PageCompound, ref frozen by page_ref_freeze */
     lruvec = folio_lruvec_lock(folio);
 
     ClearPageHasHWPoisoned(head);
 
     for (i = nr - 1; i >= 1; i--) {
         __split_huge_page_tail(head, i, lruvec, list);
         /* Some pages can be beyond EOF: drop them from page cache */
         if (head[i].index >= end) {
             struct folio *tail = page_folio(head + i);
 
             if (shmem_mapping(head->mapping))
                 shmem_uncharge(head->mapping->host, 1);
             else if (folio_test_clear_dirty(tail))
                 folio_account_cleaned(tail,
                     inode_to_wb(folio->mapping->host));
             __filemap_remove_folio(tail, NULL);
             folio_put(tail);
         } else if (!PageAnon(page)) {
             __xa_store(&head->mapping->i_pages, head[i].index,
                     head + i, 0);
         } else if (swap_cache) {
             __xa_store(&swap_cache->i_pages, offset + i,
                     head + i, 0);
         }
     }
 
     ClearPageCompound(head);
     unlock_page_lruvec(lruvec);
     /* Caller disabled irqs, so they are still disabled here */
 
     split_page_owner(head, nr);
 
     /* See comment in __split_huge_page_tail() */
     if (PageAnon(head)) {
         /* Additional pin to swap cache */
         if (PageSwapCache(head)) {
             page_ref_add(head, 2);
             xa_unlock(&swap_cache->i_pages);
         } else {
             page_ref_inc(head);
         }
     } else {
         /* Additional pin to page cache */
         page_ref_add(head, 2);
         xa_unlock(&head->mapping->i_pages);
     }
     local_irq_enable();
 
     remap_page(folio, nr);
 
     if (PageSwapCache(head)) {
         swp_entry_t entry = { .val = page_private(head) };
 
         split_swap_cluster(entry);
     }
 
     for (i = 0; i < nr; i++) {
         struct page *subpage = head + i;
         if (subpage == page)
             continue;
         unlock_page(subpage);
 
         /*
          * Subpages may be freed if there wasn't any mapping
          * like if add_to_swap() is running on a lru page that
          * had its mapping zapped. And freeing these pages
          * requires taking the lru_lock so we do the put_page
          * of the tail pages after the split is complete.
          */
         free_page_and_swap_cache(subpage);
     }
 }
 
 /* Racy check whether the huge page can be split */
 bool can_split_folio(struct folio *folio, int *pextra_pins)
 {
     int extra_pins;
 
     /* Additional pins from page cache */
     if (folio_test_anon(folio))
         extra_pins = folio_test_swapcache(folio) ?
                 folio_nr_pages(folio) : 0;
     else
         extra_pins = folio_nr_pages(folio);
     if (pextra_pins)
         *pextra_pins = extra_pins;
     return folio_mapcount(folio) == folio_ref_count(folio) - extra_pins - 1;
 }
 
 /*
  * This function splits huge page into normal pages. @page can point to any
  * subpage of huge page to split. Split doesn't change the position of @page.
  *
  * Only caller must hold pin on the @page, otherwise split fails with -EBUSY.
  * The huge page must be locked.
  *
  * If @list is null, tail pages will be added to LRU list, otherwise, to @list.
  *
  * Both head page and tail pages will inherit mapping, flags, and so on from
  * the hugepage.
  *
  * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if
  * they are not mapped.
  *
  * Returns 0 if the hugepage is split successfully.
  * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under
  * us.
  */
 int split_huge_page_to_list(struct page *page, struct list_head *list)
 {
     struct folio *folio = page_folio(page);
     struct page *head = &folio->page;
     struct deferred_split *ds_queue = get_deferred_split_queue(head);
     XA_STATE(xas, &head->mapping->i_pages, head->index);
     struct anon_vma *anon_vma = NULL;
     struct address_space *mapping = NULL;
     int extra_pins, ret;
     pgoff_t end;
     bool is_hzp;
 
     VM_BUG_ON_PAGE(!PageLocked(head), head);
     VM_BUG_ON_PAGE(!PageCompound(head), head);
 
     is_hzp = is_huge_zero_page(head);
     VM_WARN_ON_ONCE_PAGE(is_hzp, head);
     if (is_hzp)
         return -EBUSY;
 
     if (PageWriteback(head))
         return -EBUSY;
 
     if (PageAnon(head)) {
         /*
          * The caller does not necessarily hold an mmap_lock that would
          * prevent the anon_vma disappearing so we first we take a
          * reference to it and then lock the anon_vma for write. This
          * is similar to folio_lock_anon_vma_read except the write lock
          * is taken to serialise against parallel split or collapse
          * operations.
          */
         anon_vma = page_get_anon_vma(head);
         if (!anon_vma) {
             ret = -EBUSY;
             goto out;
         }
         end = -1;
         mapping = NULL;
         anon_vma_lock_write(anon_vma);
     } else {
         mapping = head->mapping;
 
         /* Truncated ? */
         if (!mapping) {
             ret = -EBUSY;
             goto out;
         }
 
         xas_split_alloc(&xas, head, compound_order(head),
                 mapping_gfp_mask(mapping) & GFP_RECLAIM_MASK);
         if (xas_error(&xas)) {
             ret = xas_error(&xas);
             goto out;
         }
 
         anon_vma = NULL;
         i_mmap_lock_read(mapping);
 
         /*
          *__split_huge_page() may need to trim off pages beyond EOF:
          * but on 32-bit, i_size_read() takes an irq-unsafe seqlock,
          * which cannot be nested inside the page tree lock. So note
          * end now: i_size itself may be changed at any moment, but
          * head page lock is good enough to serialize the trimming.
          */
         end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
         if (shmem_mapping(mapping))
             end = shmem_fallocend(mapping->host, end);
     }
 
     /*
      * Racy check if we can split the page, before unmap_page() will
      * split PMDs
      */
     if (!can_split_folio(folio, &extra_pins)) {
         ret = -EBUSY;
         goto out_unlock;
     }
 
     unmap_page(head);
 
     /* block interrupt reentry in xa_lock and spinlock */
     local_irq_disable();
     if (mapping) {
         /*
          * Check if the head page is present in page cache.
          * We assume all tail are present too, if head is there.
          */
         xas_lock(&xas);
         xas_reset(&xas);
         if (xas_load(&xas) != head)
             goto fail;
     }
 
     /* Prevent deferred_split_scan() touching ->_refcount */
     spin_lock(&ds_queue->split_queue_lock);
     if (page_ref_freeze(head, 1 + extra_pins)) {
         if (!list_empty(page_deferred_list(head))) {
             ds_queue->split_queue_len--;
             list_del(page_deferred_list(head));
         }
         spin_unlock(&ds_queue->split_queue_lock);
         if (mapping) {
             int nr = thp_nr_pages(head);
 
             xas_split(&xas, head, thp_order(head));
             if (PageSwapBacked(head)) {
                 __mod_lruvec_page_state(head, NR_SHMEM_THPS,
                             -nr);
             } else {
                 __mod_lruvec_page_state(head, NR_FILE_THPS,
                             -nr);
                 filemap_nr_thps_dec(mapping);
             }
         }
 
         __split_huge_page(page, list, end);
         ret = 0;
     } else {
         spin_unlock(&ds_queue->split_queue_lock);
 fail:
         if (mapping)
             xas_unlock(&xas);
         local_irq_enable();
         remap_page(folio, folio_nr_pages(folio));
         ret = -EBUSY;
     }
 
 out_unlock:
     if (anon_vma) {
         anon_vma_unlock_write(anon_vma);
         put_anon_vma(anon_vma);
     }
     if (mapping)
         i_mmap_unlock_read(mapping);
 out:
     xas_destroy(&xas);
     count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
     return ret;
 }
 
 void free_transhuge_page(struct page *page)
 {
     struct deferred_split *ds_queue = get_deferred_split_queue(page);
     unsigned long flags;
 
     spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
     if (!list_empty(page_deferred_list(page))) {
         ds_queue->split_queue_len--;
         list_del(page_deferred_list(page));
     }
     spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
     free_compound_page(page);
 }
 
 void deferred_split_huge_page(struct page *page)
 {
     struct deferred_split *ds_queue = get_deferred_split_queue(page);
 #ifdef CONFIG_MEMCG
     struct mem_cgroup *memcg = page_memcg(compound_head(page));
 #endif
     unsigned long flags;
 
     VM_BUG_ON_PAGE(!PageTransHuge(page), page);
 
     /*
      * The try_to_unmap() in page reclaim path might reach here too,
      * this may cause a race condition to corrupt deferred split queue.
      * And, if page reclaim is already handling the same page, it is
      * unnecessary to handle it again in shrinker.
      *
      * Check PageSwapCache to determine if the page is being
      * handled by page reclaim since THP swap would add the page into
      * swap cache before calling try_to_unmap().
      */
     if (PageSwapCache(page))
         return;
 
     spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
     if (list_empty(page_deferred_list(page))) {
         count_vm_event(THP_DEFERRED_SPLIT_PAGE);
         list_add_tail(page_deferred_list(page), &ds_queue->split_queue);
         ds_queue->split_queue_len++;
 #ifdef CONFIG_MEMCG
         if (memcg)
             set_shrinker_bit(memcg, page_to_nid(page),
                      deferred_split_shrinker.id);
 #endif
     }
     spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
 }
 
 static unsigned long deferred_split_count(struct shrinker *shrink,
         struct shrink_control *sc)
 {
     struct pglist_data *pgdata = NODE_DATA(sc->nid);
     struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
 
 #ifdef CONFIG_MEMCG
     if (sc->memcg)
         ds_queue = &sc->memcg->deferred_split_queue;
 #endif
     return READ_ONCE(ds_queue->split_queue_len);
 }
 
 static unsigned long deferred_split_scan(struct shrinker *shrink,
         struct shrink_control *sc)
 {
     struct pglist_data *pgdata = NODE_DATA(sc->nid);
     struct deferred_split *ds_queue = &pgdata->deferred_split_queue;
     unsigned long flags;
     LIST_HEAD(list), *pos, *next;
     struct page *page;
     int split = 0;
 
 #ifdef CONFIG_MEMCG
     if (sc->memcg)
         ds_queue = &sc->memcg->deferred_split_queue;
 #endif
 
     spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
     /* Take pin on all head pages to avoid freeing them under us */
     list_for_each_safe(pos, next, &ds_queue->split_queue) {
         page = list_entry((void *)pos, struct page, deferred_list);
         page = compound_head(page);
         if (get_page_unless_zero(page)) {
             list_move(page_deferred_list(page), &list);
         } else {
             /* We lost race with put_compound_page() */
             list_del_init(page_deferred_list(page));
             ds_queue->split_queue_len--;
         }
         if (!--sc->nr_to_scan)
             break;
     }
     spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
 
     list_for_each_safe(pos, next, &list) {
         page = list_entry((void *)pos, struct page, deferred_list);
         if (!trylock_page(page))
             goto next;
         /* split_huge_page() removes page from list on success */
         if (!split_huge_page(page))
             split++;
         unlock_page(page);
 next:
         put_page(page);
     }
 
     spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
     list_splice_tail(&list, &ds_queue->split_queue);
     spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
 
     /*
      * Stop shrinker if we didn't split any page, but the queue is empty.
      * This can happen if pages were freed under us.
      */
     if (!split && list_empty(&ds_queue->split_queue))
         return SHRINK_STOP;
     return split;
 }
 
 static struct shrinker deferred_split_shrinker = {
     .count_objects = deferred_split_count,
     .scan_objects = deferred_split_scan,
     .seeks = DEFAULT_SEEKS,
     .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE |
          SHRINKER_NONSLAB,
 };
 
 #ifdef CONFIG_DEBUG_FS
 static void split_huge_pages_all(void)
 {
     struct zone *zone;
     struct page *page;
     unsigned long pfn, max_zone_pfn;
     unsigned long total = 0, split = 0;
 
     pr_debug("Split all THPs\n");
     for_each_zone(zone) {
         if (!managed_zone(zone))
             continue;
         max_zone_pfn = zone_end_pfn(zone);
         for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
             int nr_pages;
 
             page = pfn_to_online_page(pfn);
             if (!page || !get_page_unless_zero(page))
                 continue;
 
             if (zone != page_zone(page))
                 goto next;
 
             if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
                 goto next;
 
             total++;
             lock_page(page);
             nr_pages = thp_nr_pages(page);
             if (!split_huge_page(page))
                 split++;
             pfn += nr_pages - 1;
             unlock_page(page);
 next:
             put_page(page);
             cond_resched();
         }
     }
 
     pr_debug("%lu of %lu THP split\n", split, total);
 }
 
 static inline bool vma_not_suitable_for_thp_split(struct vm_area_struct *vma)
 {
     return vma_is_special_huge(vma) || (vma->vm_flags & VM_IO) ||
             is_vm_hugetlb_page(vma);
 }
 
 static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
                 unsigned long vaddr_end)
 {
     int ret = 0;
     struct task_struct *task;
     struct mm_struct *mm;
     unsigned long total = 0, split = 0;
     unsigned long addr;
 
     vaddr_start &= PAGE_MASK;
     vaddr_end &= PAGE_MASK;
 
     /* Find the task_struct from pid */
     rcu_read_lock();
     task = find_task_by_vpid(pid);
     if (!task) {
         rcu_read_unlock();
         ret = -ESRCH;
         goto out;
     }
     get_task_struct(task);
     rcu_read_unlock();
 
     /* Find the mm_struct */
     mm = get_task_mm(task);
     put_task_struct(task);
 
     if (!mm) {
         ret = -EINVAL;
         goto out;
     }
 
     pr_debug("Split huge pages in pid: %d, vaddr: [0x%lx - 0x%lx]\n",
          pid, vaddr_start, vaddr_end);
 
     mmap_read_lock(mm);
     /*
      * always increase addr by PAGE_SIZE, since we could have a PTE page
      * table filled with PTE-mapped THPs, each of which is distinct.
      */
     for (addr = vaddr_start; addr < vaddr_end; addr += PAGE_SIZE) {
         struct vm_area_struct *vma = vma_lookup(mm, addr);
         struct page *page;
 
         if (!vma)
             break;
 
         /* skip special VMA and hugetlb VMA */
         if (vma_not_suitable_for_thp_split(vma)) {
             addr = vma->vm_end;
             continue;
         }
 
         /* FOLL_DUMP to ignore special (like zero) pages */
         page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
 
         if (IS_ERR_OR_NULL(page) || is_zone_device_page(page))
             continue;
 
         if (!is_transparent_hugepage(page))
             goto next;
 
         total++;
         if (!can_split_folio(page_folio(page), NULL))
             goto next;
 
         if (!trylock_page(page))
             goto next;
 
         if (!split_huge_page(page))
             split++;
 
         unlock_page(page);
 next:
         put_page(page);
         cond_resched();
     }
     mmap_read_unlock(mm);
     mmput(mm);
 
     pr_debug("%lu of %lu THP split\n", split, total);
 
 out:
     return ret;
 }
 
 static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
                 pgoff_t off_end)
 {
     struct filename *file;
     struct file *candidate;
     struct address_space *mapping;
     int ret = -EINVAL;
     pgoff_t index;
     int nr_pages = 1;
     unsigned long total = 0, split = 0;
 
     file = getname_kernel(file_path);
     if (IS_ERR(file))
         return ret;
 
     candidate = file_open_name(file, O_RDONLY, 0);
     if (IS_ERR(candidate))
         goto out;
 
     pr_debug("split file-backed THPs in file: %s, page offset: [0x%lx - 0x%lx]\n",
          file_path, off_start, off_end);
 
     mapping = candidate->f_mapping;
 
     for (index = off_start; index < off_end; index += nr_pages) {
         struct page *fpage = pagecache_get_page(mapping, index,
                         FGP_ENTRY | FGP_HEAD, 0);
 
         nr_pages = 1;
         if (xa_is_value(fpage) || !fpage)
             continue;
 
         if (!is_transparent_hugepage(fpage))
             goto next;
 
         total++;
         nr_pages = thp_nr_pages(fpage);
 
         if (!trylock_page(fpage))
             goto next;
 
         if (!split_huge_page(fpage))
             split++;
 
         unlock_page(fpage);
 next:
         put_page(fpage);
         cond_resched();
     }
 
     filp_close(candidate, NULL);
     ret = 0;
 
     pr_debug("%lu of %lu file-backed THP split\n", split, total);
 out:
     putname(file);
     return ret;
 }
 
 #define MAX_INPUT_BUF_SZ 255
 
 static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
                 size_t count, loff_t *ppops)
 {
     static DEFINE_MUTEX(split_debug_mutex);
     ssize_t ret;
     /* hold pid, start_vaddr, end_vaddr or file_path, off_start, off_end */
     char input_buf[MAX_INPUT_BUF_SZ];
     int pid;
     unsigned long vaddr_start, vaddr_end;
 
     ret = mutex_lock_interruptible(&split_debug_mutex);
     if (ret)
         return ret;
 
     ret = -EFAULT;
 
     memset(input_buf, 0, MAX_INPUT_BUF_SZ);
     if (copy_from_user(input_buf, buf, min_t(size_t, count, MAX_INPUT_BUF_SZ)))
         goto out;
 
     input_buf[MAX_INPUT_BUF_SZ - 1] = '\0';
 
     if (input_buf[0] == '/') {
         char *tok;
         char *buf = input_buf;
         char file_path[MAX_INPUT_BUF_SZ];
         pgoff_t off_start = 0, off_end = 0;
         size_t input_len = strlen(input_buf);
 
         tok = strsep(&buf, ",");
         if (tok) {
             strcpy(file_path, tok);
         } else {
             ret = -EINVAL;
             goto out;
         }
 
         ret = sscanf(buf, "0x%lx,0x%lx", &off_start, &off_end);
         if (ret != 2) {
             ret = -EINVAL;
             goto out;
         }
         ret = split_huge_pages_in_file(file_path, off_start, off_end);
         if (!ret)
             ret = input_len;
 
         goto out;
     }
 
     ret = sscanf(input_buf, "%d,0x%lx,0x%lx", &pid, &vaddr_start, &vaddr_end);
     if (ret == 1 && pid == 1) {
         split_huge_pages_all();
         ret = strlen(input_buf);
         goto out;
     } else if (ret != 3) {
         ret = -EINVAL;
         goto out;
     }
 
     ret = split_huge_pages_pid(pid, vaddr_start, vaddr_end);
     if (!ret)
         ret = strlen(input_buf);
 out:
     mutex_unlock(&split_debug_mutex);
     return ret;
 
 }
 
 static const struct file_operations split_huge_pages_fops = {
     .owner   = THIS_MODULE,
     .write   = split_huge_pages_write,
     .llseek  = no_llseek,
 };
 
 static int __init split_huge_pages_debugfs(void)
 {
     debugfs_create_file("split_huge_pages", 0200, NULL, NULL,
                 &split_huge_pages_fops);
     return 0;
 }
 late_initcall(split_huge_pages_debugfs);
 #endif
 
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
 int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
         struct page *page)
 {
     struct vm_area_struct *vma = pvmw->vma;
     struct mm_struct *mm = vma->vm_mm;
     unsigned long address = pvmw->address;
     bool anon_exclusive;
     pmd_t pmdval;
     swp_entry_t entry;
     pmd_t pmdswp;
 
     if (!(pvmw->pmd && !pvmw->pte))
         return 0;
 
     flush_cache_range(vma, address, address + HPAGE_PMD_SIZE);
     pmdval = pmdp_invalidate(vma, address, pvmw->pmd);
 
     anon_exclusive = PageAnon(page) && PageAnonExclusive(page);
     if (anon_exclusive && page_try_share_anon_rmap(page)) {
         set_pmd_at(mm, address, pvmw->pmd, pmdval);
         return -EBUSY;
     }
 
     if (pmd_dirty(pmdval))
         set_page_dirty(page);
     if (pmd_write(pmdval))
         entry = make_writable_migration_entry(page_to_pfn(page));
     else if (anon_exclusive)
         entry = make_readable_exclusive_migration_entry(page_to_pfn(page));
     else
         entry = make_readable_migration_entry(page_to_pfn(page));
     pmdswp = swp_entry_to_pmd(entry);
     if (pmd_soft_dirty(pmdval))
         pmdswp = pmd_swp_mksoft_dirty(pmdswp);
     set_pmd_at(mm, address, pvmw->pmd, pmdswp);
     page_remove_rmap(page, vma, true);
     put_page(page);
     trace_set_migration_pmd(address, pmd_val(pmdswp));
 
     return 0;
 }
 
 void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 {
     struct vm_area_struct *vma = pvmw->vma;
     struct mm_struct *mm = vma->vm_mm;
     unsigned long address = pvmw->address;
     unsigned long haddr = address & HPAGE_PMD_MASK;
     pmd_t pmde;
     swp_entry_t entry;
 
     if (!(pvmw->pmd && !pvmw->pte))
         return;
 
     entry = pmd_to_swp_entry(*pvmw->pmd);
     get_page(new);
     pmde = pmd_mkold(mk_huge_pmd(new, READ_ONCE(vma->vm_page_prot)));
     if (pmd_swp_soft_dirty(*pvmw->pmd))
         pmde = pmd_mksoft_dirty(pmde);
     if (is_writable_migration_entry(entry))
         pmde = maybe_pmd_mkwrite(pmde, vma);
     if (pmd_swp_uffd_wp(*pvmw->pmd))
         pmde = pmd_wrprotect(pmd_mkuffd_wp(pmde));
 
     if (PageAnon(new)) {
         rmap_t rmap_flags = RMAP_COMPOUND;
 
         if (!is_readable_migration_entry(entry))
             rmap_flags |= RMAP_EXCLUSIVE;
 
         page_add_anon_rmap(new, vma, haddr, rmap_flags);
     } else {
         page_add_file_rmap(new, vma, true);
     }
     VM_BUG_ON(pmd_write(pmde) && PageAnon(new) && !PageAnonExclusive(new));
     set_pmd_at(mm, haddr, pvmw->pmd, pmde);
 
     /* No need to invalidate - it was non-present before */
     update_mmu_cache_pmd(vma, address, pvmw->pmd);
     trace_remove_migration_pmd(address, pmd_val(pmde));
 }
 #endif