/*
   * mm/rmap.c - physical to virtual reverse mappings
   *
   * Copyright 2001, Rik van Riel <riel@conectiva.com.br>
   * Released under the General Public License (GPL).
   *
   * Simple, low overhead reverse mapping scheme.
   * Please try to keep this thing as modular as possible.
   *
   * Provides methods for unmapping each kind of mapped page:
   * the anon methods track anonymous pages, and
   * the file methods track pages belonging to an inode.
   *
   * Original design by Rik van Riel <riel@conectiva.com.br> 2001
   * File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004
   * Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004

   * Contributions by Hugh Dickins 2003, 2004

   */
  
  /*
   * Lock ordering in mm:
   *

   * inode->i_mutex	(while writing or truncating, not reading or faulting)

   *   mm->mmap_sem
   *     page->flags PG_locked (lock_page)

   *       hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share)
   *         mapping->i_mmap_rwsem
   *           anon_vma->rwsem
   *             mm->page_table_lock or pte_lock

   *               pgdat->lru_lock (in mark_page_accessed, isolate_lru_page)

   *               swap_lock (in swap_duplicate, swap_info_get)
   *                 mmlist_lock (in mmput, drain_mmlist and others)
   *                 mapping->private_lock (in __set_page_dirty_buffers)
   *                   mem_cgroup_{begin,end}_page_stat (memcg->move_lock)

   *                     i_pages lock (widely used)

   *                 inode->i_lock (in set_page_dirty's __mark_inode_dirty)
   *                 bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
   *                   sb_lock (within inode_lock in fs/fs-writeback.c)

   *                   i_pages lock (widely used, in set_page_dirty,

   *                             in arch-dependent flush_dcache_mmap_lock,
   *                             within bdi.wb->list_lock in __sync_single_inode)

   *

   * anon_vma->rwsem,mapping->i_mutex      (memory_failure, collect_procs_anon)

   *   ->tasklist_lock

   *     pte map lock

   */
  
  #include <linux/mm.h>

  #include <linux/sched/mm.h>

  #include <linux/sched/task.h>

  #include <linux/pagemap.h>
  #include <linux/swap.h>
  #include <linux/swapops.h>
  #include <linux/slab.h>
  #include <linux/init.h>

  #include <linux/ksm.h>

  #include <linux/rmap.h>
  #include <linux/rcupdate.h>

  #include <linux/export.h>

  #include <linux/memcontrol.h>

  #include <linux/mmu_notifier.h>

  #include <linux/migrate.h>

  #include <linux/hugetlb.h>

  #include <linux/huge_mm.h>

  #include <linux/backing-dev.h>

  #include <linux/page_idle.h>

  #include <linux/memremap.h>

  #include <linux/userfaultfd_k.h>

  
  #include <asm/tlbflush.h>

  #include <trace/events/tlb.h>

  #include "internal.h"

  static struct kmem_cache *anon_vma_cachep;

  static struct kmem_cache *anon_vma_chain_cachep;

  
  static inline struct anon_vma *anon_vma_alloc(void)
  {

  	struct anon_vma *anon_vma;
  
  	anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
  	if (anon_vma) {
  		atomic_set(&anon_vma->refcount, 1);

  		anon_vma->degree = 1;	/* Reference for first vma */
  		anon_vma->parent = anon_vma;

  		/*
  		 * Initialise the anon_vma root to point to itself. If called
  		 * from fork, the root will be reset to the parents anon_vma.
  		 */
  		anon_vma->root = anon_vma;
  	}
  
  	return anon_vma;

  }

  static inline void anon_vma_free(struct anon_vma *anon_vma)

  {

  	VM_BUG_ON(atomic_read(&anon_vma->refcount));

  
  	/*

  	 * Synchronize against page_lock_anon_vma_read() such that

  	 * we can safely hold the lock without the anon_vma getting
  	 * freed.
  	 *
  	 * Relies on the full mb implied by the atomic_dec_and_test() from
  	 * put_anon_vma() against the acquire barrier implied by

  	 * down_read_trylock() from page_lock_anon_vma_read(). This orders:

  	 *

  	 * page_lock_anon_vma_read()	VS	put_anon_vma()
  	 *   down_read_trylock()		  atomic_dec_and_test()

  	 *   LOCK				  MB

  	 *   atomic_read()			  rwsem_is_locked()

  	 *
  	 * LOCK should suffice since the actual taking of the lock must
  	 * happen _before_ what follows.
  	 */

  	might_sleep();

  	if (rwsem_is_locked(&anon_vma->root->rwsem)) {

  		anon_vma_lock_write(anon_vma);

  		anon_vma_unlock_write(anon_vma);

  	}

  	kmem_cache_free(anon_vma_cachep, anon_vma);
  }

  static inline struct anon_vma_chain *anon_vma_chain_alloc(gfp_t gfp)

  {

  	return kmem_cache_alloc(anon_vma_chain_cachep, gfp);

  }

  static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)

  {
  	kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
  }

  static void anon_vma_chain_link(struct vm_area_struct *vma,
  				struct anon_vma_chain *avc,
  				struct anon_vma *anon_vma)
  {
  	avc->vma = vma;
  	avc->anon_vma = anon_vma;
  	list_add(&avc->same_vma, &vma->anon_vma_chain);

  	anon_vma_interval_tree_insert(avc, &anon_vma->rb_root);

  }

  /**

   * __anon_vma_prepare - attach an anon_vma to a memory region

   * @vma: the memory region in question
   *
   * This makes sure the memory mapping described by 'vma' has
   * an 'anon_vma' attached to it, so that we can associate the
   * anonymous pages mapped into it with that anon_vma.
   *

   * The common case will be that we already have one, which
   * is handled inline by anon_vma_prepare(). But if

   * not we either need to find an adjacent mapping that we

   * can re-use the anon_vma from (very common when the only
   * reason for splitting a vma has been mprotect()), or we
   * allocate a new one.
   *
   * Anon-vma allocations are very subtle, because we may have

   * optimistically looked up an anon_vma in page_lock_anon_vma_read()

   * and that may actually touch the spinlock even in the newly
   * allocated vma (it depends on RCU to make sure that the
   * anon_vma isn't actually destroyed).
   *
   * As a result, we need to do proper anon_vma locking even
   * for the new allocation. At the same time, we do not want
   * to do any locking for the common case of already having
   * an anon_vma.
   *
   * This must be called with the mmap_sem held for reading.
   */

  int __anon_vma_prepare(struct vm_area_struct *vma)

  {

  	struct mm_struct *mm = vma->vm_mm;
  	struct anon_vma *anon_vma, *allocated;

  	struct anon_vma_chain *avc;

  
  	might_sleep();

  	avc = anon_vma_chain_alloc(GFP_KERNEL);
  	if (!avc)
  		goto out_enomem;
  
  	anon_vma = find_mergeable_anon_vma(vma);
  	allocated = NULL;
  	if (!anon_vma) {
  		anon_vma = anon_vma_alloc();
  		if (unlikely(!anon_vma))
  			goto out_enomem_free_avc;
  		allocated = anon_vma;
  	}

  	anon_vma_lock_write(anon_vma);
  	/* page_table_lock to protect against threads */
  	spin_lock(&mm->page_table_lock);
  	if (likely(!vma->anon_vma)) {
  		vma->anon_vma = anon_vma;
  		anon_vma_chain_link(vma, avc, anon_vma);
  		/* vma reference or self-parent link for new root */
  		anon_vma->degree++;

  		allocated = NULL;

  		avc = NULL;
  	}
  	spin_unlock(&mm->page_table_lock);
  	anon_vma_unlock_write(anon_vma);

  	if (unlikely(allocated))
  		put_anon_vma(allocated);
  	if (unlikely(avc))
  		anon_vma_chain_free(avc);

  	return 0;

  
   out_enomem_free_avc:
  	anon_vma_chain_free(avc);
   out_enomem:
  	return -ENOMEM;

  }

  /*
   * This is a useful helper function for locking the anon_vma root as
   * we traverse the vma->anon_vma_chain, looping over anon_vma's that
   * have the same vma.
   *
   * Such anon_vma's should have the same root, so you'd expect to see
   * just a single mutex_lock for the whole traversal.
   */
  static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *root, struct anon_vma *anon_vma)
  {
  	struct anon_vma *new_root = anon_vma->root;
  	if (new_root != root) {
  		if (WARN_ON_ONCE(root))

  			up_write(&root->rwsem);

  		root = new_root;

  		down_write(&root->rwsem);

  	}
  	return root;
  }
  
  static inline void unlock_anon_vma_root(struct anon_vma *root)
  {
  	if (root)

  		up_write(&root->rwsem);

  }

  /*
   * Attach the anon_vmas from src to dst.
   * Returns 0 on success, -ENOMEM on failure.

   *
   * If dst->anon_vma is NULL this function tries to find and reuse existing
   * anon_vma which has no vmas and only one child anon_vma. This prevents
   * degradation of anon_vma hierarchy to endless linear chain in case of
   * constantly forking task. On the other hand, an anon_vma with more than one
   * child isn't reused even if there was no alive vma, thus rmap walker has a
   * good chance of avoiding scanning the whole hierarchy when it searches where
   * page is mapped.

   */
  int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)

  {

  	struct anon_vma_chain *avc, *pavc;

  	struct anon_vma *root = NULL;

  	list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {

  		struct anon_vma *anon_vma;

  		avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
  		if (unlikely(!avc)) {
  			unlock_anon_vma_root(root);
  			root = NULL;
  			avc = anon_vma_chain_alloc(GFP_KERNEL);
  			if (!avc)
  				goto enomem_failure;
  		}

  		anon_vma = pavc->anon_vma;
  		root = lock_anon_vma_root(root, anon_vma);
  		anon_vma_chain_link(dst, avc, anon_vma);

  
  		/*
  		 * Reuse existing anon_vma if its degree lower than two,
  		 * that means it has no vma and only one anon_vma child.
  		 *
  		 * Do not chose parent anon_vma, otherwise first child
  		 * will always reuse it. Root anon_vma is never reused:
  		 * it has self-parent reference and at least one child.
  		 */
  		if (!dst->anon_vma && anon_vma != src->anon_vma &&
  				anon_vma->degree < 2)
  			dst->anon_vma = anon_vma;

  	}

  	if (dst->anon_vma)
  		dst->anon_vma->degree++;

  	unlock_anon_vma_root(root);

  	return 0;

   enomem_failure:

  	/*
  	 * dst->anon_vma is dropped here otherwise its degree can be incorrectly
  	 * decremented in unlink_anon_vmas().
  	 * We can safely do this because callers of anon_vma_clone() don't care
  	 * about dst->anon_vma if anon_vma_clone() failed.
  	 */
  	dst->anon_vma = NULL;

  	unlink_anon_vmas(dst);
  	return -ENOMEM;

  }

  /*
   * Attach vma to its own anon_vma, as well as to the anon_vmas that
   * the corresponding VMA in the parent process is attached to.
   * Returns 0 on success, non-zero on failure.
   */
  int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)

  {

  	struct anon_vma_chain *avc;
  	struct anon_vma *anon_vma;

  	int error;

  	/* Don't bother if the parent process has no anon_vma here. */
  	if (!pvma->anon_vma)
  		return 0;

  	/* Drop inherited anon_vma, we'll reuse existing or allocate new. */
  	vma->anon_vma = NULL;

  	/*
  	 * First, attach the new VMA to the parent VMA's anon_vmas,
  	 * so rmap can find non-COWed pages in child processes.
  	 */

  	error = anon_vma_clone(vma, pvma);
  	if (error)
  		return error;

  	/* An existing anon_vma has been reused, all done then. */
  	if (vma->anon_vma)
  		return 0;

  	/* Then add our own anon_vma. */
  	anon_vma = anon_vma_alloc();
  	if (!anon_vma)
  		goto out_error;

  	avc = anon_vma_chain_alloc(GFP_KERNEL);

  	if (!avc)
  		goto out_error_free_anon_vma;

  
  	/*
  	 * The root anon_vma's spinlock is the lock actually used when we
  	 * lock any of the anon_vmas in this anon_vma tree.
  	 */
  	anon_vma->root = pvma->anon_vma->root;

  	anon_vma->parent = pvma->anon_vma;

  	/*

  	 * With refcounts, an anon_vma can stay around longer than the
  	 * process it belongs to. The root anon_vma needs to be pinned until
  	 * this anon_vma is freed, because the lock lives in the root.

  	 */
  	get_anon_vma(anon_vma->root);

  	/* Mark this anon_vma as the one where our new (COWed) pages go. */
  	vma->anon_vma = anon_vma;

  	anon_vma_lock_write(anon_vma);

  	anon_vma_chain_link(vma, avc, anon_vma);

  	anon_vma->parent->degree++;

  	anon_vma_unlock_write(anon_vma);

  
  	return 0;
  
   out_error_free_anon_vma:

  	put_anon_vma(anon_vma);

   out_error:

  	unlink_anon_vmas(vma);

  	return -ENOMEM;

  }

  void unlink_anon_vmas(struct vm_area_struct *vma)
  {
  	struct anon_vma_chain *avc, *next;

  	struct anon_vma *root = NULL;

  	/*
  	 * Unlink each anon_vma chained to the VMA.  This list is ordered
  	 * from newest to oldest, ensuring the root anon_vma gets freed last.
  	 */

  	list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {

  		struct anon_vma *anon_vma = avc->anon_vma;
  
  		root = lock_anon_vma_root(root, anon_vma);

  		anon_vma_interval_tree_remove(avc, &anon_vma->rb_root);

  
  		/*
  		 * Leave empty anon_vmas on the list - we'll need
  		 * to free them outside the lock.
  		 */

  		if (RB_EMPTY_ROOT(&anon_vma->rb_root.rb_root)) {

  			anon_vma->parent->degree--;

  			continue;

  		}

  
  		list_del(&avc->same_vma);
  		anon_vma_chain_free(avc);
  	}

  	if (vma->anon_vma)
  		vma->anon_vma->degree--;

  	unlock_anon_vma_root(root);
  
  	/*
  	 * Iterate the list once more, it now only contains empty and unlinked
  	 * anon_vmas, destroy them. Could not do before due to __put_anon_vma()

  	 * needing to write-acquire the anon_vma->root->rwsem.

  	 */
  	list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
  		struct anon_vma *anon_vma = avc->anon_vma;

  		VM_WARN_ON(anon_vma->degree);

  		put_anon_vma(anon_vma);

  		list_del(&avc->same_vma);
  		anon_vma_chain_free(avc);
  	}
  }

  static void anon_vma_ctor(void *data)

  {

  	struct anon_vma *anon_vma = data;

  	init_rwsem(&anon_vma->rwsem);

  	atomic_set(&anon_vma->refcount, 0);

  	anon_vma->rb_root = RB_ROOT_CACHED;

  }
  
  void __init anon_vma_init(void)
  {
  	anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),

  			0, SLAB_TYPESAFE_BY_RCU|SLAB_PANIC|SLAB_ACCOUNT,

  			anon_vma_ctor);
  	anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain,
  			SLAB_PANIC|SLAB_ACCOUNT);

  }
  
  /*

   * Getting a lock on a stable anon_vma from a page off the LRU is tricky!
   *
   * Since there is no serialization what so ever against page_remove_rmap()
   * the best this function can do is return a locked anon_vma that might
   * have been relevant to this page.
   *
   * The page might have been remapped to a different anon_vma or the anon_vma
   * returned may already be freed (and even reused).
   *

   * In case it was remapped to a different anon_vma, the new anon_vma will be a
   * child of the old anon_vma, and the anon_vma lifetime rules will therefore
   * ensure that any anon_vma obtained from the page will still be valid for as
   * long as we observe page_mapped() [ hence all those page_mapped() tests ].
   *

   * All users of this function must be very careful when walking the anon_vma
   * chain and verify that the page in question is indeed mapped in it
   * [ something equivalent to page_mapped_in_vma() ].
   *
   * Since anon_vma's slab is DESTROY_BY_RCU and we know from page_remove_rmap()
   * that the anon_vma pointer from page->mapping is valid if there is a
   * mapcount, we can dereference the anon_vma after observing those.

   */

  struct anon_vma *page_get_anon_vma(struct page *page)

  {

  	struct anon_vma *anon_vma = NULL;

  	unsigned long anon_mapping;
  
  	rcu_read_lock();

  	anon_mapping = (unsigned long)READ_ONCE(page->mapping);

  	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)

  		goto out;
  	if (!page_mapped(page))
  		goto out;
  
  	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);

  	if (!atomic_inc_not_zero(&anon_vma->refcount)) {
  		anon_vma = NULL;
  		goto out;
  	}

  
  	/*
  	 * If this page is still mapped, then its anon_vma cannot have been

  	 * freed.  But if it has been unmapped, we have no security against the
  	 * anon_vma structure being freed and reused (for another anon_vma:

  	 * SLAB_TYPESAFE_BY_RCU guarantees that - so the atomic_inc_not_zero()

  	 * above cannot corrupt).

  	 */

  	if (!page_mapped(page)) {

  		rcu_read_unlock();

  		put_anon_vma(anon_vma);

  		return NULL;

  	}

  out:
  	rcu_read_unlock();

  
  	return anon_vma;
  }

  /*
   * Similar to page_get_anon_vma() except it locks the anon_vma.
   *
   * Its a little more complex as it tries to keep the fast path to a single
   * atomic op -- the trylock. If we fail the trylock, we fall back to getting a
   * reference like with page_get_anon_vma() and then block on the mutex.
   */

  struct anon_vma *page_lock_anon_vma_read(struct page *page)

  {

  	struct anon_vma *anon_vma = NULL;

  	struct anon_vma *root_anon_vma;

  	unsigned long anon_mapping;

  	rcu_read_lock();

  	anon_mapping = (unsigned long)READ_ONCE(page->mapping);

  	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
  		goto out;
  	if (!page_mapped(page))
  		goto out;
  
  	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);

  	root_anon_vma = READ_ONCE(anon_vma->root);

  	if (down_read_trylock(&root_anon_vma->rwsem)) {

  		/*

  		 * If the page is still mapped, then this anon_vma is still
  		 * its anon_vma, and holding the mutex ensures that it will

  		 * not go away, see anon_vma_free().

  		 */

  		if (!page_mapped(page)) {

  			up_read(&root_anon_vma->rwsem);

  			anon_vma = NULL;
  		}
  		goto out;
  	}

  	/* trylock failed, we got to sleep */
  	if (!atomic_inc_not_zero(&anon_vma->refcount)) {
  		anon_vma = NULL;
  		goto out;
  	}
  
  	if (!page_mapped(page)) {

  		rcu_read_unlock();

  		put_anon_vma(anon_vma);

  		return NULL;

  	}
  
  	/* we pinned the anon_vma, its safe to sleep */
  	rcu_read_unlock();

  	anon_vma_lock_read(anon_vma);

  
  	if (atomic_dec_and_test(&anon_vma->refcount)) {
  		/*
  		 * Oops, we held the last refcount, release the lock
  		 * and bail -- can't simply use put_anon_vma() because

  		 * we'll deadlock on the anon_vma_lock_write() recursion.

  		 */

  		anon_vma_unlock_read(anon_vma);

  		__put_anon_vma(anon_vma);
  		anon_vma = NULL;
  	}
  
  	return anon_vma;
  
  out:
  	rcu_read_unlock();

  	return anon_vma;

  }

  void page_unlock_anon_vma_read(struct anon_vma *anon_vma)

  {

  	anon_vma_unlock_read(anon_vma);

  }

  #ifdef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH

  /*
   * Flush TLB entries for recently unmapped pages from remote CPUs. It is
   * important if a PTE was dirty when it was unmapped that it's flushed
   * before any IO is initiated on the page to prevent lost writes. Similarly,
   * it must be flushed before freeing to prevent data leakage.
   */
  void try_to_unmap_flush(void)
  {
  	struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;

  
  	if (!tlb_ubc->flush_required)
  		return;

  	arch_tlbbatch_flush(&tlb_ubc->arch);

  	tlb_ubc->flush_required = false;

  	tlb_ubc->writable = false;

  }

  /* Flush iff there are potentially writable TLB entries that can race with IO */
  void try_to_unmap_flush_dirty(void)
  {
  	struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
  
  	if (tlb_ubc->writable)
  		try_to_unmap_flush();
  }

  static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)

  {
  	struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;

  	arch_tlbbatch_add_mm(&tlb_ubc->arch, mm);

  	tlb_ubc->flush_required = true;

  
  	/*

  	 * Ensure compiler does not re-order the setting of tlb_flush_batched
  	 * before the PTE is cleared.
  	 */
  	barrier();
  	mm->tlb_flush_batched = true;
  
  	/*

  	 * If the PTE was dirty then it's best to assume it's writable. The
  	 * caller must use try_to_unmap_flush_dirty() or try_to_unmap_flush()
  	 * before the page is queued for IO.
  	 */
  	if (writable)
  		tlb_ubc->writable = true;

  }
  
  /*
   * Returns true if the TLB flush should be deferred to the end of a batch of
   * unmap operations to reduce IPIs.
   */
  static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
  {
  	bool should_defer = false;
  
  	if (!(flags & TTU_BATCH_FLUSH))
  		return false;
  
  	/* If remote CPUs need to be flushed then defer batch the flush */
  	if (cpumask_any_but(mm_cpumask(mm), get_cpu()) < nr_cpu_ids)
  		should_defer = true;
  	put_cpu();
  
  	return should_defer;
  }

  
  /*
   * Reclaim unmaps pages under the PTL but do not flush the TLB prior to
   * releasing the PTL if TLB flushes are batched. It's possible for a parallel
   * operation such as mprotect or munmap to race between reclaim unmapping
   * the page and flushing the page. If this race occurs, it potentially allows
   * access to data via a stale TLB entry. Tracking all mm's that have TLB
   * batching in flight would be expensive during reclaim so instead track
   * whether TLB batching occurred in the past and if so then do a flush here
   * if required. This will cost one additional flush per reclaim cycle paid
   * by the first operation at risk such as mprotect and mumap.
   *
   * This must be called under the PTL so that an access to tlb_flush_batched
   * that is potentially a "reclaim vs mprotect/munmap/etc" race will synchronise
   * via the PTL.
   */
  void flush_tlb_batched_pending(struct mm_struct *mm)
  {
  	if (mm->tlb_flush_batched) {
  		flush_tlb_mm(mm);
  
  		/*
  		 * Do not allow the compiler to re-order the clearing of
  		 * tlb_flush_batched before the tlb is flushed.
  		 */
  		barrier();
  		mm->tlb_flush_batched = false;
  	}
  }

  #else

  static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)

  {
  }
  
  static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
  {
  	return false;
  }
  #endif /* CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH */

  /*

   * At what user virtual address is page expected in vma?

   * Caller should check the page is actually part of the vma.

   */
  unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
  {

  	unsigned long address;

  	if (PageAnon(page)) {

  		struct anon_vma *page__anon_vma = page_anon_vma(page);
  		/*
  		 * Note: swapoff's unuse_vma() is more efficient with this
  		 * check, and needs it to match anon_vma when KSM is active.
  		 */
  		if (!vma->anon_vma || !page__anon_vma ||
  		    vma->anon_vma->root != page__anon_vma->root)

  			return -EFAULT;

  	} else if (page->mapping) {
  		if (!vma->vm_file || vma->vm_file->f_mapping != page->mapping)

  			return -EFAULT;
  	} else
  		return -EFAULT;

  	address = __vma_address(page, vma);
  	if (unlikely(address < vma->vm_start || address >= vma->vm_end))
  		return -EFAULT;
  	return address;

  }

  pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
  {
  	pgd_t *pgd;

  	p4d_t *p4d;

  	pud_t *pud;
  	pmd_t *pmd = NULL;

  	pmd_t pmde;

  
  	pgd = pgd_offset(mm, address);
  	if (!pgd_present(*pgd))
  		goto out;

  	p4d = p4d_offset(pgd, address);
  	if (!p4d_present(*p4d))
  		goto out;
  
  	pud = pud_offset(p4d, address);

  	if (!pud_present(*pud))
  		goto out;
  
  	pmd = pmd_offset(pud, address);

  	/*

  	 * Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at()

  	 * without holding anon_vma lock for write.  So when looking for a
  	 * genuine pmde (in which to find pte), test present and !THP together.
  	 */

  	pmde = *pmd;
  	barrier();

  	if (!pmd_present(pmde) || pmd_trans_huge(pmde))

  		pmd = NULL;
  out:
  	return pmd;
  }

  struct page_referenced_arg {
  	int mapcount;
  	int referenced;
  	unsigned long vm_flags;
  	struct mem_cgroup *memcg;
  };
  /*
   * arg: page_referenced_arg will be passed
   */

  static bool page_referenced_one(struct page *page, struct vm_area_struct *vma,

  			unsigned long address, void *arg)
  {

  	struct page_referenced_arg *pra = arg;

  	struct page_vma_mapped_walk pvmw = {
  		.page = page,
  		.vma = vma,
  		.address = address,
  	};

  	int referenced = 0;

  	while (page_vma_mapped_walk(&pvmw)) {
  		address = pvmw.address;

  		if (vma->vm_flags & VM_LOCKED) {
  			page_vma_mapped_walk_done(&pvmw);
  			pra->vm_flags |= VM_LOCKED;

  			return false; /* To break the loop */

  		}

  		if (pvmw.pte) {
  			if (ptep_clear_flush_young_notify(vma, address,
  						pvmw.pte)) {
  				/*
  				 * Don't treat a reference through
  				 * a sequentially read mapping as such.
  				 * If the page has been used in another mapping,
  				 * we will catch it; if this other mapping is
  				 * already gone, the unmap path will have set
  				 * PG_referenced or activated the page.
  				 */
  				if (likely(!(vma->vm_flags & VM_SEQ_READ)))
  					referenced++;
  			}
  		} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
  			if (pmdp_clear_flush_young_notify(vma, address,
  						pvmw.pmd))

  				referenced++;

  		} else {
  			/* unexpected pmd-mapped page? */
  			WARN_ON_ONCE(1);

  		}

  
  		pra->mapcount--;

  	}

  	if (referenced)
  		clear_page_idle(page);
  	if (test_and_clear_page_young(page))
  		referenced++;

  	if (referenced) {
  		pra->referenced++;
  		pra->vm_flags |= vma->vm_flags;

  	}

  	if (!pra->mapcount)

  		return false; /* To break the loop */

  	return true;

  }

  static bool invalid_page_referenced_vma(struct vm_area_struct *vma, void *arg)

  {

  	struct page_referenced_arg *pra = arg;
  	struct mem_cgroup *memcg = pra->memcg;

  	if (!mm_match_cgroup(vma->vm_mm, memcg))
  		return true;

  	return false;

  }
  
  /**
   * page_referenced - test if the page was referenced
   * @page: the page to test
   * @is_locked: caller holds lock on the page

   * @memcg: target memory cgroup

   * @vm_flags: collect encountered vma->vm_flags who actually referenced the page

   *
   * Quick test_and_clear_referenced for all mappings to a page,
   * returns the number of ptes which referenced the page.
   */

  int page_referenced(struct page *page,
  		    int is_locked,

  		    struct mem_cgroup *memcg,

  		    unsigned long *vm_flags)

  {

  	int we_locked = 0;

  	struct page_referenced_arg pra = {

  		.mapcount = total_mapcount(page),

  		.memcg = memcg,
  	};
  	struct rmap_walk_control rwc = {
  		.rmap_one = page_referenced_one,
  		.arg = (void *)&pra,
  		.anon_lock = page_lock_anon_vma_read,
  	};

  	*vm_flags = 0;

  	if (!pra.mapcount)

  		return 0;
  
  	if (!page_rmapping(page))
  		return 0;
  
  	if (!is_locked && (!PageAnon(page) || PageKsm(page))) {
  		we_locked = trylock_page(page);
  		if (!we_locked)
  			return 1;

  	}

  
  	/*
  	 * If we are reclaiming on behalf of a cgroup, skip
  	 * counting on behalf of references from different
  	 * cgroups
  	 */
  	if (memcg) {
  		rwc.invalid_vma = invalid_page_referenced_vma;
  	}

  	rmap_walk(page, &rwc);

  	*vm_flags = pra.vm_flags;
  
  	if (we_locked)
  		unlock_page(page);
  
  	return pra.referenced;

  }

  static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma,

  			    unsigned long address, void *arg)

  {

  	struct page_vma_mapped_walk pvmw = {
  		.page = page,
  		.vma = vma,
  		.address = address,
  		.flags = PVMW_SYNC,
  	};

  	struct mmu_notifier_range range;

  	int *cleaned = arg;

  	/*
  	 * We have to assume the worse case ie pmd for invalidation. Note that
  	 * the page can not be free from this function.
  	 */

  	mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_PAGE,
  				0, vma, vma->vm_mm, address,

  				min(vma->vm_end, address + page_size(page)));

  	mmu_notifier_invalidate_range_start(&range);

  	while (page_vma_mapped_walk(&pvmw)) {
  		int ret = 0;

  		address = pvmw.address;

  		if (pvmw.pte) {
  			pte_t entry;
  			pte_t *pte = pvmw.pte;
  
  			if (!pte_dirty(*pte) && !pte_write(*pte))
  				continue;

  			flush_cache_page(vma, address, pte_pfn(*pte));
  			entry = ptep_clear_flush(vma, address, pte);

  			entry = pte_wrprotect(entry);
  			entry = pte_mkclean(entry);

  			set_pte_at(vma->vm_mm, address, pte, entry);

  			ret = 1;
  		} else {
  #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
  			pmd_t *pmd = pvmw.pmd;
  			pmd_t entry;
  
  			if (!pmd_dirty(*pmd) && !pmd_write(*pmd))
  				continue;

  			flush_cache_page(vma, address, page_to_pfn(page));

  			entry = pmdp_invalidate(vma, address, pmd);

  			entry = pmd_wrprotect(entry);
  			entry = pmd_mkclean(entry);

  			set_pmd_at(vma->vm_mm, address, pmd, entry);

  			ret = 1;
  #else
  			/* unexpected pmd-mapped page? */
  			WARN_ON_ONCE(1);
  #endif
  		}

  		/*
  		 * No need to call mmu_notifier_invalidate_range() as we are
  		 * downgrading page table protection not changing it to point
  		 * to a new page.
  		 *

  		 * See Documentation/vm/mmu_notifier.rst

  		 */
  		if (ret)

  			(*cleaned)++;

  	}

  	mmu_notifier_invalidate_range_end(&range);

  	return true;

  }

  static bool invalid_mkclean_vma(struct vm_area_struct *vma, void *arg)

  {

  	if (vma->vm_flags & VM_SHARED)

  		return false;

  	return true;

  }
  
  int page_mkclean(struct page *page)
  {

  	int cleaned = 0;
  	struct address_space *mapping;
  	struct rmap_walk_control rwc = {
  		.arg = (void *)&cleaned,
  		.rmap_one = page_mkclean_one,
  		.invalid_vma = invalid_mkclean_vma,
  	};

  
  	BUG_ON(!PageLocked(page));

  	if (!page_mapped(page))
  		return 0;
  
  	mapping = page_mapping(page);
  	if (!mapping)
  		return 0;
  
  	rmap_walk(page, &rwc);

  	return cleaned;

  }

  EXPORT_SYMBOL_GPL(page_mkclean);

  /**

   * page_move_anon_rmap - move a page to our anon_vma
   * @page:	the page to move to our anon_vma
   * @vma:	the vma the page belongs to

   *
   * When a page belongs exclusively to one process after a COW event,
   * that page can be moved into the anon_vma that belongs to just that
   * process, so the rmap code will not search the parent or sibling
   * processes.
   */

  void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma)

  {
  	struct anon_vma *anon_vma = vma->anon_vma;

  	page = compound_head(page);

  	VM_BUG_ON_PAGE(!PageLocked(page), page);

  	VM_BUG_ON_VMA(!anon_vma, vma);

  
  	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;

  	/*
  	 * Ensure that anon_vma and the PAGE_MAPPING_ANON bit are written
  	 * simultaneously, so a concurrent reader (eg page_referenced()'s
  	 * PageAnon()) will not see one without the other.
  	 */
  	WRITE_ONCE(page->mapping, (struct address_space *) anon_vma);

  }
  
  /**

   * __page_set_anon_rmap - set up new anonymous rmap

   * @page:	Page or Hugepage to add to rmap

   * @vma:	VM area to add page to.
   * @address:	User virtual address of the mapping	

   * @exclusive:	the page is exclusively owned by the current process

   */
  static void __page_set_anon_rmap(struct page *page,

  	struct vm_area_struct *vma, unsigned long address, int exclusive)

  {

  	struct anon_vma *anon_vma = vma->anon_vma;

  	BUG_ON(!anon_vma);

  	if (PageAnon(page))
  		return;

  	/*

  	 * If the page isn't exclusively mapped into this vma,
  	 * we must use the _oldest_ possible anon_vma for the
  	 * page mapping!

  	 */

  	if (!exclusive)

  		anon_vma = anon_vma->root;

  	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
  	page->mapping = (struct address_space *) anon_vma;

  	page->index = linear_page_index(vma, address);

  }
  
  /**

   * __page_check_anon_rmap - sanity check anonymous rmap addition

   * @page:	the page to add the mapping to
   * @vma:	the vm area in which the mapping is added
   * @address:	the user virtual address mapped
   */
  static void __page_check_anon_rmap(struct page *page,
  	struct vm_area_struct *vma, unsigned long address)
  {
  #ifdef CONFIG_DEBUG_VM
  	/*
  	 * The page's anon-rmap details (mapping and index) are guaranteed to
  	 * be set up correctly at this point.
  	 *
  	 * We have exclusion against page_add_anon_rmap because the caller
  	 * always holds the page locked, except if called from page_dup_rmap,
  	 * in which case the page is already known to be setup.
  	 *
  	 * We have exclusion against page_add_new_anon_rmap because those pages
  	 * are initially only visible via the pagetables, and the pte is locked
  	 * over the call to page_add_new_anon_rmap.
  	 */

  	BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);

  	BUG_ON(page_to_pgoff(page) != linear_page_index(vma, address));

  #endif
  }
  
  /**

   * page_add_anon_rmap - add pte mapping to an anonymous page
   * @page:	the page to add the mapping to
   * @vma:	the vm area in which the mapping is added
   * @address:	the user virtual address mapped

   * @compound:	charge the page as compound or small page

   *

   * The caller needs to hold the pte lock, and the page must be locked in

   * the anon_vma case: to serialize mapping,index checking after setting,
   * and to ensure that PageAnon is not being upgraded racily to PageKsm
   * (but PageKsm is never downgraded to PageAnon).

   */
  void page_add_anon_rmap(struct page *page,

  	struct vm_area_struct *vma, unsigned long address, bool compound)

  {

  	do_page_add_anon_rmap(page, vma, address, compound ? RMAP_COMPOUND : 0);

  }
  
  /*
   * Special version of the above for do_swap_page, which often runs
   * into pages that are exclusively owned by the current process.
   * Everybody else should continue to use page_add_anon_rmap above.
   */
  void do_page_add_anon_rmap(struct page *page,

  	struct vm_area_struct *vma, unsigned long address, int flags)

  {

  	bool compound = flags & RMAP_COMPOUND;
  	bool first;

  	if (compound) {
  		atomic_t *mapcount;

  		VM_BUG_ON_PAGE(!PageLocked(page), page);

  		VM_BUG_ON_PAGE(!PageTransHuge(page), page);
  		mapcount = compound_mapcount_ptr(page);
  		first = atomic_inc_and_test(mapcount);

  	} else {
  		first = atomic_inc_and_test(&page->_mapcount);
  	}

  	if (first) {

  		int nr = compound ? hpage_nr_pages(page) : 1;

  		/*
  		 * We use the irq-unsafe __{inc|mod}_zone_page_stat because
  		 * these counters are not modified in interrupt context, and
  		 * pte lock(a spinlock) is held, which implies preemption
  		 * disabled.
  		 */

  		if (compound)

  			__inc_node_page_state(page, NR_ANON_THPS);

  		__mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, nr);

  	}

  	if (unlikely(PageKsm(page)))
  		return;

  	VM_BUG_ON_PAGE(!PageLocked(page), page);

  	/* address might be in next vma when migration races vma_adjust */

  	if (first)

  		__page_set_anon_rmap(page, vma, address,
  				flags & RMAP_EXCLUSIVE);

  	else

  		__page_check_anon_rmap(page, vma, address);

  }

  /**

   * page_add_new_anon_rmap - add pte mapping to a new anonymous page
   * @page:	the page to add the mapping to
   * @vma:	the vm area in which the mapping is added
   * @address:	the user virtual address mapped

   * @compound:	charge the page as compound or small page

   *
   * Same as page_add_anon_rmap but must only be called on *new* pages.
   * This means the inc-and-test can be bypassed.

   * Page does not have to be locked.

   */
  void page_add_new_anon_rmap(struct page *page,

  	struct vm_area_struct *vma, unsigned long address, bool compound)

  {

  	int nr = compound ? hpage_nr_pages(page) : 1;

  	VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);

  	__SetPageSwapBacked(page);

  	if (compound) {
  		VM_BUG_ON_PAGE(!PageTransHuge(page), page);

  		/* increment count (starts at -1) */
  		atomic_set(compound_mapcount_ptr(page), 0);

  		__inc_node_page_state(page, NR_ANON_THPS);

  	} else {
  		/* Anon THP always mapped first with PMD */
  		VM_BUG_ON_PAGE(PageTransCompound(page), page);
  		/* increment count (starts at -1) */
  		atomic_set(&page->_mapcount, 0);

  	}

  	__mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, nr);

  	__page_set_anon_rmap(page, vma, address, 1);

  }

  /**
   * page_add_file_rmap - add pte mapping to a file page
   * @page: the page to add the mapping to

   * @compound: charge the page as compound or small page

   *

   * The caller needs to hold the pte lock.

   */

  void page_add_file_rmap(struct page *page, bool compound)

  {

  	int i, nr = 1;
  
  	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);

  	lock_page_memcg(page);

  	if (compound && PageTransHuge(page)) {
  		for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
  			if (atomic_inc_and_test(&page[i]._mapcount))
  				nr++;
  		}
  		if (!atomic_inc_and_test(compound_mapcount_ptr(page)))
  			goto out;

  		if (PageSwapBacked(page))
  			__inc_node_page_state(page, NR_SHMEM_PMDMAPPED);
  		else
  			__inc_node_page_state(page, NR_FILE_PMDMAPPED);

  	} else {

  		if (PageTransCompound(page) && page_mapping(page)) {
  			VM_WARN_ON_ONCE(!PageLocked(page));

  			SetPageDoubleMap(compound_head(page));
  			if (PageMlocked(page))
  				clear_page_mlock(compound_head(page));
  		}

  		if (!atomic_inc_and_test(&page->_mapcount))
  			goto out;

  	}

  	__mod_lruvec_page_state(page, NR_FILE_MAPPED, nr);

  out:

  	unlock_page_memcg(page);

  }

  static void page_remove_file_rmap(struct page *page, bool compound)

  {

  	int i, nr = 1;

  	VM_BUG_ON_PAGE(compound && !PageHead(page), page);

  	lock_page_memcg(page);

  	/* Hugepages are not counted in NR_FILE_MAPPED for now. */
  	if (unlikely(PageHuge(page))) {
  		/* hugetlb pages are always mapped with pmds */
  		atomic_dec(compound_mapcount_ptr(page));

  		goto out;

  	}

  	/* page still mapped by someone else? */

  	if (compound && PageTransHuge(page)) {
  		for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
  			if (atomic_add_negative(-1, &page[i]._mapcount))
  				nr++;
  		}
  		if (!atomic_add_negative(-1, compound_mapcount_ptr(page)))
  			goto out;

  		if (PageSwapBacked(page))
  			__dec_node_page_state(page, NR_SHMEM_PMDMAPPED);
  		else
  			__dec_node_page_state(page, NR_FILE_PMDMAPPED);

  	} else {
  		if (!atomic_add_negative(-1, &page->_mapcount))
  			goto out;
  	}

  
  	/*

  	 * We use the irq-unsafe __{inc|mod}_lruvec_page_state because

  	 * these counters are not modified in interrupt context, and
  	 * pte lock(a spinlock) is held, which implies preemption disabled.
  	 */

  	__mod_lruvec_page_state(page, NR_FILE_MAPPED, -nr);

  
  	if (unlikely(PageMlocked(page)))
  		clear_page_mlock(page);
  out:

  	unlock_page_memcg(page);

  }

  static void page_remove_anon_compound_rmap(struct page *page)
  {
  	int i, nr;
  
  	if (!atomic_add_negative(-1, compound_mapcount_ptr(page)))
  		return;
  
  	/* Hugepages are not counted in NR_ANON_PAGES for now. */
  	if (unlikely(PageHuge(page)))
  		return;
  
  	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
  		return;

  	__dec_node_page_state(page, NR_ANON_THPS);

  
  	if (TestClearPageDoubleMap(page)) {
  		/*
  		 * Subpages can be mapped with PTEs too. Check how many of
  		 * themi are still mapped.
  		 */
  		for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
  			if (atomic_add_negative(-1, &page[i]._mapcount))
  				nr++;
  		}
  	} else {
  		nr = HPAGE_PMD_NR;
  	}

  	if (unlikely(PageMlocked(page)))
  		clear_page_mlock(page);

  	if (nr) {

  		__mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);

  		deferred_split_huge_page(page);
  	}

  }

  /**
   * page_remove_rmap - take down pte mapping from a page

   * @page:	page to remove mapping from
   * @compound:	uncharge the page as compound or small page

   *

   * The caller needs to hold the pte lock.

   */

  void page_remove_rmap(struct page *page, bool compound)

  {

  	if (!PageAnon(page))
  		return page_remove_file_rmap(page, compound);

  	if (compound)
  		return page_remove_anon_compound_rmap(page);

  	/* page still mapped by someone else? */
  	if (!atomic_add_negative(-1, &page->_mapcount))

  		return;

  	/*

  	 * We use the irq-unsafe __{inc|mod}_zone_page_stat because
  	 * these counters are not modified in interrupt context, and

  	 * pte lock(a spinlock) is held, which implies preemption disabled.

  	 */

  	__dec_node_page_state(page, NR_ANON_MAPPED);

  	if (unlikely(PageMlocked(page)))
  		clear_page_mlock(page);

  	if (PageTransCompound(page))
  		deferred_split_huge_page(compound_head(page));

  	/*
  	 * It would be tidy to reset the PageAnon mapping here,
  	 * but that might overwrite a racing page_add_anon_rmap
  	 * which increments mapcount after us but sets mapping

  	 * before us: so leave the reset to free_unref_page,

  	 * and remember that it's only reliable while mapped.
  	 * Leaving it set also helps swapoff to reinstate ptes
  	 * faster for those pages still in swapcache.
  	 */

  }
  
  /*

   * @arg: enum ttu_flags will be passed to this argument

   */

  static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,

  		     unsigned long address, void *arg)

  {
  	struct mm_struct *mm = vma->vm_mm;

  	struct page_vma_mapped_walk pvmw = {
  		.page = page,
  		.vma = vma,
  		.address = address,
  	};

  	pte_t pteval;

  	struct page *subpage;

  	bool ret = true;

  	struct mmu_notifier_range range;

  	enum ttu_flags flags = (enum ttu_flags)arg;

  	/* munlock has nothing to gain from examining un-locked vmas */
  	if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))

  		return true;

  	if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
  	    is_zone_device_page(page) && !is_device_private_page(page))
  		return true;

  	if (flags & TTU_SPLIT_HUGE_PMD) {
  		split_huge_pmd_address(vma, address,

  				flags & TTU_SPLIT_FREEZE, page);

  	}

  	/*

  	 * For THP, we have to assume the worse case ie pmd for invalidation.
  	 * For hugetlb, it could be much worse if we need to do pud
  	 * invalidation in the case of pmd sharing.
  	 *
  	 * Note that the page can not be free in this function as call of
  	 * try_to_unmap() must hold a reference on the page.

  	 */

  	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,

  				address,

  				min(vma->vm_end, address + page_size(page)));

  	if (PageHuge(page)) {
  		/*
  		 * If sharing is possible, start and end will be adjusted
  		 * accordingly.
  		 */

  		adjust_range_if_pmd_sharing_possible(vma, &range.start,
  						     &range.end);

  	}

  	mmu_notifier_invalidate_range_start(&range);

  	while (page_vma_mapped_walk(&pvmw)) {

  #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
  		/* PMD-mapped THP migration entry */
  		if (!pvmw.pte && (flags & TTU_MIGRATION)) {
  			VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page), page);

  			set_pmd_migration_entry(&pvmw, page);
  			continue;
  		}
  #endif

  		/*
  		 * If the page is mlock()d, we cannot swap it out.
  		 * If it's recently referenced (perhaps page_referenced
  		 * skipped over this mm) then we should reactivate it.
  		 */
  		if (!(flags & TTU_IGNORE_MLOCK)) {
  			if (vma->vm_flags & VM_LOCKED) {
  				/* PTE-mapped THP are never mlocked */
  				if (!PageTransCompound(page)) {
  					/*
  					 * Holding pte lock, we do *not* need
  					 * mmap_sem here
  					 */
  					mlock_vma_page(page);
  				}

  				ret = false;

  				page_vma_mapped_walk_done(&pvmw);
  				break;

  			}

  			if (flags & TTU_MUNLOCK)
  				continue;

  		}

  		/* Unexpected PMD-mapped THP? */
  		VM_BUG_ON_PAGE(!pvmw.pte, page);
  
  		subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte);

  		address = pvmw.address;

  		if (PageHuge(page)) {
  			if (huge_pmd_unshare(mm, &address, pvmw.pte)) {
  				/*
  				 * huge_pmd_unshare unmapped an entire PMD
  				 * page.  There is no way of knowing exactly
  				 * which PMDs may be cached for this mm, so
  				 * we must flush them all.  start/end were
  				 * already adjusted above to cover this range.
  				 */

  				flush_cache_range(vma, range.start, range.end);
  				flush_tlb_range(vma, range.start, range.end);
  				mmu_notifier_invalidate_range(mm, range.start,
  							      range.end);

  
  				/*
  				 * The ref count of the PMD page was dropped
  				 * which is part of the way map counting
  				 * is done for shared PMDs.  Return 'true'
  				 * here.  When there is no other sharing,
  				 * huge_pmd_unshare returns false and we will
  				 * unmap the actual page and drop map count
  				 * to zero.
  				 */
  				page_vma_mapped_walk_done(&pvmw);
  				break;
  			}
  		}

  		if (IS_ENABLED(CONFIG_MIGRATION) &&
  		    (flags & TTU_MIGRATION) &&
  		    is_zone_device_page(page)) {
  			swp_entry_t entry;
  			pte_t swp_pte;
  
  			pteval = ptep_get_and_clear(mm, pvmw.address, pvmw.pte);
  
  			/*
  			 * Store the pfn of the page in a special migration
  			 * pte. do_swap_page() will wait until the migration
  			 * pte is removed and then restart fault handling.
  			 */
  			entry = make_migration_entry(page, 0);
  			swp_pte = swp_entry_to_pte(entry);
  			if (pte_soft_dirty(pteval))
  				swp_pte = pte_swp_mksoft_dirty(swp_pte);
  			set_pte_at(mm, pvmw.address, pvmw.pte, swp_pte);

  			/*
  			 * No need to invalidate here it will synchronize on
  			 * against the special swap migration pte.

  			 *
  			 * The assignment to subpage above was computed from a
  			 * swap PTE which results in an invalid pointer.
  			 * Since only PAGE_SIZE pages can currently be
  			 * migrated, just set it to page. This will need to be
  			 * changed when hugepage migrations to device private
  			 * memory are supported.

  			 */

  			subpage = page;

  			goto discard;
  		}

  		if (!(flags & TTU_IGNORE_ACCESS)) {

  			if (ptep_clear_flush_young_notify(vma, address,

  						pvmw.pte)) {

  				ret = false;

  				page_vma_mapped_walk_done(&pvmw);
  				break;
  			}

  		}

  		/* Nuke the page table entry. */

  		flush_cache_page(vma, address, pte_pfn(*pvmw.pte));

  		if (should_defer_flush(mm, flags)) {
  			/*
  			 * We clear the PTE but do not flush so potentially
  			 * a remote CPU could still be writing to the page.
  			 * If the entry was previously clean then the
  			 * architecture must guarantee that a clear->dirty
  			 * transition on a cached TLB entry is written through
  			 * and traps if the PTE is unmapped.
  			 */

  			pteval = ptep_get_and_clear(mm, address, pvmw.pte);

  
  			set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
  		} else {

  			pteval = ptep_clear_flush(vma, address, pvmw.pte);

  		}

  		/* Move the dirty bit to the page. Now the pte is gone. */
  		if (pte_dirty(pteval))
  			set_page_dirty(page);

  		/* Update high watermark before we lower rss */
  		update_hiwater_rss(mm);

  		if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {

  			pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));

  			if (PageHuge(page)) {

  				hugetlb_count_sub(compound_nr(page), mm);

  				set_huge_swap_pte_at(mm, address,

  						     pvmw.pte, pteval,
  						     vma_mmu_pagesize(vma));

  			} else {
  				dec_mm_counter(mm, mm_counter(page));

  				set_pte_at(mm, address, pvmw.pte, pteval);

  			}

  		} else if (pte_unused(pteval) && !userfaultfd_armed(vma)) {

  			/*
  			 * The guest indicated that the page content is of no
  			 * interest anymore. Simply discard the pte, vmscan
  			 * will take care of the rest.

  			 * A future reference will then fault in a new zero
  			 * page. When userfaultfd is active, we must not drop
  			 * this page though, as its main user (postcopy
  			 * migration) will not expect userfaults on already
  			 * copied pages.

  			 */

  			dec_mm_counter(mm, mm_counter(page));

  			/* We have to invalidate as we cleared the pte */
  			mmu_notifier_invalidate_range(mm, address,
  						      address + PAGE_SIZE);

  		} else if (IS_ENABLED(CONFIG_MIGRATION) &&

  				(flags & (TTU_MIGRATION|TTU_SPLIT_FREEZE))) {

  			swp_entry_t entry;
  			pte_t swp_pte;

  
  			if (arch_unmap_one(mm, vma, address, pteval) < 0) {
  				set_pte_at(mm, address, pvmw.pte, pteval);
  				ret = false;
  				page_vma_mapped_walk_done(&pvmw);
  				break;
  			}

  			/*
  			 * Store the pfn of the page in a special migration
  			 * pte. do_swap_page() will wait until the migration
  			 * pte is removed and then restart fault handling.
  			 */
  			entry = make_migration_entry(subpage,
  					pte_write(pteval));
  			swp_pte = swp_entry_to_pte(entry);
  			if (pte_soft_dirty(pteval))
  				swp_pte = pte_swp_mksoft_dirty(swp_pte);

  			set_pte_at(mm, address, pvmw.pte, swp_pte);

  			/*
  			 * No need to invalidate here it will synchronize on
  			 * against the special swap migration pte.
  			 */

  		} else if (PageAnon(page)) {
  			swp_entry_t entry = { .val = page_private(subpage) };
  			pte_t swp_pte;
  			/*
  			 * Store the swap location in the pte.
  			 * See handle_pte_fault() ...
  			 */

  			if (unlikely(PageSwapBacked(page) != PageSwapCache(page))) {
  				WARN_ON_ONCE(1);

  				ret = false;

  				/* We have to invalidate as we cleared the pte */

  				mmu_notifier_invalidate_range(mm, address,
  							address + PAGE_SIZE);

  				page_vma_mapped_walk_done(&pvmw);
  				break;
  			}

  			/* MADV_FREE page check */
  			if (!PageSwapBacked(page)) {
  				if (!PageDirty(page)) {

  					/* Invalidate as we cleared the pte */
  					mmu_notifier_invalidate_range(mm,
  						address, address + PAGE_SIZE);