diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
index 203e26da5f92..e5cc8848dcb3 100644
--- a/Documentation/admin-guide/mm/userfaultfd.rst
+++ b/Documentation/admin-guide/mm/userfaultfd.rst
@@ -113,6 +113,9 @@ events, except page fault notifications, may be generated:
   areas. ``UFFD_FEATURE_MINOR_SHMEM`` is the analogous feature indicating
   support for shmem virtual memory areas.
 
+- ``UFFD_FEATURE_MOVE`` indicates that the kernel supports moving an
+  existing page contents from userspace.
+
 The userland application should set the feature flags it intends to use
 when invoking the ``UFFDIO_API`` ioctl, to request that those features be
 enabled if supported.
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index ac616cfbacf5..4149a22335e5 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -2005,6 +2005,75 @@ static inline unsigned int uffd_ctx_features(__u64 user_features)
 	return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
 }
 
+static int userfaultfd_move(struct userfaultfd_ctx *ctx,
+			    unsigned long arg)
+{
+	__s64 ret;
+	struct uffdio_move uffdio_move;
+	struct uffdio_move __user *user_uffdio_move;
+	struct userfaultfd_wake_range range;
+	struct mm_struct *mm = ctx->mm;
+
+	user_uffdio_move = (struct uffdio_move __user *) arg;
+
+	if (atomic_read(&ctx->mmap_changing))
+		return -EAGAIN;
+
+	if (copy_from_user(&uffdio_move, user_uffdio_move,
+			   /* don't copy "move" last field */
+			   sizeof(uffdio_move)-sizeof(__s64)))
+		return -EFAULT;
+
+	/* Do not allow cross-mm moves. */
+	if (mm != current->mm)
+		return -EINVAL;
+
+	ret = validate_range(mm, uffdio_move.dst, uffdio_move.len);
+	if (ret)
+		return ret;
+
+	ret = validate_range(mm, uffdio_move.src, uffdio_move.len);
+	if (ret)
+		return ret;
+
+	if (uffdio_move.mode & ~(UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES|
+				  UFFDIO_MOVE_MODE_DONTWAKE))
+		return -EINVAL;
+
+	if (mmget_not_zero(mm)) {
+		mmap_read_lock(mm);
+
+		/* Re-check after taking mmap_lock */
+		if (likely(!atomic_read(&ctx->mmap_changing)))
+			ret = move_pages(ctx, mm, uffdio_move.dst, uffdio_move.src,
+					 uffdio_move.len, uffdio_move.mode);
+		else
+			ret = -EINVAL;
+
+		mmap_read_unlock(mm);
+		mmput(mm);
+	} else {
+		return -ESRCH;
+	}
+
+	if (unlikely(put_user(ret, &user_uffdio_move->move)))
+		return -EFAULT;
+	if (ret < 0)
+		goto out;
+
+	/* len == 0 would wake all */
+	VM_WARN_ON(!ret);
+	range.len = ret;
+	if (!(uffdio_move.mode & UFFDIO_MOVE_MODE_DONTWAKE)) {
+		range.start = uffdio_move.dst;
+		wake_userfault(ctx, &range);
+	}
+	ret = range.len == uffdio_move.len ? 0 : -EAGAIN;
+
+out:
+	return ret;
+}
+
 /*
  * userland asks for a certain API version and we return which bits
  * and ioctl commands are implemented in this kernel for such API
@@ -2097,6 +2166,9 @@ static long userfaultfd_ioctl(struct file *file, unsigned cmd,
 	case UFFDIO_ZEROPAGE:
 		ret = userfaultfd_zeropage(ctx, arg);
 		break;
+	case UFFDIO_MOVE:
+		ret = userfaultfd_move(ctx, arg);
+		break;
 	case UFFDIO_WRITEPROTECT:
 		ret = userfaultfd_writeprotect(ctx, arg);
 		break;
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index b26fe858fd44..8034eda972e5 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -121,6 +121,11 @@ static inline void anon_vma_lock_write(struct anon_vma *anon_vma)
 	down_write(&anon_vma->root->rwsem);
 }
 
+static inline int anon_vma_trylock_write(struct anon_vma *anon_vma)
+{
+	return down_write_trylock(&anon_vma->root->rwsem);
+}
+
 static inline void anon_vma_unlock_write(struct anon_vma *anon_vma)
 {
 	up_write(&anon_vma->root->rwsem);
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index f2dc19f40d05..e4056547fbe6 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -93,6 +93,17 @@ extern int mwriteprotect_range(struct mm_struct *dst_mm,
 extern long uffd_wp_range(struct vm_area_struct *vma,
 			  unsigned long start, unsigned long len, bool enable_wp);
 
+/* move_pages */
+void double_pt_lock(spinlock_t *ptl1, spinlock_t *ptl2);
+void double_pt_unlock(spinlock_t *ptl1, spinlock_t *ptl2);
+ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
+		   unsigned long dst_start, unsigned long src_start,
+		   unsigned long len, __u64 flags);
+int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pmd_t dst_pmdval,
+			struct vm_area_struct *dst_vma,
+			struct vm_area_struct *src_vma,
+			unsigned long dst_addr, unsigned long src_addr);
+
 /* mm helpers */
 static inline bool is_mergeable_vm_userfaultfd_ctx(struct vm_area_struct *vma,
 					struct vm_userfaultfd_ctx vm_ctx)
diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 0dbc81015018..2841e4ea8f2c 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -41,7 +41,8 @@
 			   UFFD_FEATURE_WP_HUGETLBFS_SHMEM |	\
 			   UFFD_FEATURE_WP_UNPOPULATED |	\
 			   UFFD_FEATURE_POISON |		\
-			   UFFD_FEATURE_WP_ASYNC)
+			   UFFD_FEATURE_WP_ASYNC |		\
+			   UFFD_FEATURE_MOVE)
 #define UFFD_API_IOCTLS				\
 	((__u64)1 << _UFFDIO_REGISTER |		\
 	 (__u64)1 << _UFFDIO_UNREGISTER |	\
@@ -50,6 +51,7 @@
 	((__u64)1 << _UFFDIO_WAKE |		\
 	 (__u64)1 << _UFFDIO_COPY |		\
 	 (__u64)1 << _UFFDIO_ZEROPAGE |		\
+	 (__u64)1 << _UFFDIO_MOVE |		\
 	 (__u64)1 << _UFFDIO_WRITEPROTECT |	\
 	 (__u64)1 << _UFFDIO_CONTINUE |		\
 	 (__u64)1 << _UFFDIO_POISON)
@@ -73,6 +75,7 @@
 #define _UFFDIO_WAKE			(0x02)
 #define _UFFDIO_COPY			(0x03)
 #define _UFFDIO_ZEROPAGE		(0x04)
+#define _UFFDIO_MOVE			(0x05)
 #define _UFFDIO_WRITEPROTECT		(0x06)
 #define _UFFDIO_CONTINUE		(0x07)
 #define _UFFDIO_POISON			(0x08)
@@ -92,6 +95,8 @@
 				      struct uffdio_copy)
 #define UFFDIO_ZEROPAGE		_IOWR(UFFDIO, _UFFDIO_ZEROPAGE,	\
 				      struct uffdio_zeropage)
+#define UFFDIO_MOVE		_IOWR(UFFDIO, _UFFDIO_MOVE,	\
+				      struct uffdio_move)
 #define UFFDIO_WRITEPROTECT	_IOWR(UFFDIO, _UFFDIO_WRITEPROTECT, \
 				      struct uffdio_writeprotect)
 #define UFFDIO_CONTINUE		_IOWR(UFFDIO, _UFFDIO_CONTINUE,	\
@@ -222,6 +227,9 @@ struct uffdio_api {
 	 * asynchronous mode is supported in which the write fault is
 	 * automatically resolved and write-protection is un-set.
 	 * It implies UFFD_FEATURE_WP_UNPOPULATED.
+	 *
+	 * UFFD_FEATURE_MOVE indicates that the kernel supports moving an
+	 * existing page contents from userspace.
 	 */
 #define UFFD_FEATURE_PAGEFAULT_FLAG_WP		(1<<0)
 #define UFFD_FEATURE_EVENT_FORK			(1<<1)
@@ -239,6 +247,7 @@ struct uffdio_api {
 #define UFFD_FEATURE_WP_UNPOPULATED		(1<<13)
 #define UFFD_FEATURE_POISON			(1<<14)
 #define UFFD_FEATURE_WP_ASYNC			(1<<15)
+#define UFFD_FEATURE_MOVE			(1<<16)
 	__u64 features;
 
 	__u64 ioctls;
@@ -347,6 +356,24 @@ struct uffdio_poison {
 	__s64 updated;
 };
 
+struct uffdio_move {
+	__u64 dst;
+	__u64 src;
+	__u64 len;
+	/*
+	 * Especially if used to atomically remove memory from the
+	 * address space the wake on the dst range is not needed.
+	 */
+#define UFFDIO_MOVE_MODE_DONTWAKE		((__u64)1<<0)
+#define UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES	((__u64)1<<1)
+	__u64 mode;
+	/*
+	 * "move" is written by the ioctl and must be at the end: the
+	 * copy_from_user will not read the last 8 bytes.
+	 */
+	__s64 move;
+};
+
 /*
  * Flags for the userfaultfd(2) system call itself.
  */
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f31f02472396..967786f49134 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1964,6 +1964,128 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	return ret;
 }
 
+#ifdef CONFIG_USERFAULTFD
+/*
+ * The PT lock for src_pmd and the mmap_lock for reading are held by
+ * the caller, but it must return after releasing the page_table_lock.
+ * Just move the page from src_pmd to dst_pmd if possible.
+ * Return zero if succeeded in moving the page, -EAGAIN if it needs to be
+ * repeated by the caller, or other errors in case of failure.
+ */
+int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pmd_t dst_pmdval,
+			struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
+			unsigned long dst_addr, unsigned long src_addr)
+{
+	pmd_t _dst_pmd, src_pmdval;
+	struct page *src_page;
+	struct folio *src_folio;
+	struct anon_vma *src_anon_vma;
+	spinlock_t *src_ptl, *dst_ptl;
+	pgtable_t src_pgtable;
+	struct mmu_notifier_range range;
+	int err = 0;
+
+	src_pmdval = *src_pmd;
+	src_ptl = pmd_lockptr(mm, src_pmd);
+
+	lockdep_assert_held(src_ptl);
+	mmap_assert_locked(mm);
+
+	/* Sanity checks before the operation */
+	if (WARN_ON_ONCE(!pmd_none(dst_pmdval)) || WARN_ON_ONCE(src_addr & ~HPAGE_PMD_MASK) ||
+	    WARN_ON_ONCE(dst_addr & ~HPAGE_PMD_MASK)) {
+		spin_unlock(src_ptl);
+		return -EINVAL;
+	}
+
+	if (!pmd_trans_huge(src_pmdval)) {
+		spin_unlock(src_ptl);
+		if (is_pmd_migration_entry(src_pmdval)) {
+			pmd_migration_entry_wait(mm, &src_pmdval);
+			return -EAGAIN;
+		}
+		return -ENOENT;
+	}
+
+	src_page = pmd_page(src_pmdval);
+	if (unlikely(!PageAnonExclusive(src_page))) {
+		spin_unlock(src_ptl);
+		return -EBUSY;
+	}
+
+	src_folio = page_folio(src_page);
+	folio_get(src_folio);
+	spin_unlock(src_ptl);
+
+	flush_cache_range(src_vma, src_addr, src_addr + HPAGE_PMD_SIZE);
+	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, src_addr,
+				src_addr + HPAGE_PMD_SIZE);
+	mmu_notifier_invalidate_range_start(&range);
+
+	folio_lock(src_folio);
+
+	/*
+	 * split_huge_page walks the anon_vma chain without the page
+	 * lock. Serialize against it with the anon_vma lock, the page
+	 * lock is not enough.
+	 */
+	src_anon_vma = folio_get_anon_vma(src_folio);
+	if (!src_anon_vma) {
+		err = -EAGAIN;
+		goto unlock_folio;
+	}
+	anon_vma_lock_write(src_anon_vma);
+
+	dst_ptl = pmd_lockptr(mm, dst_pmd);
+	double_pt_lock(src_ptl, dst_ptl);
+	if (unlikely(!pmd_same(*src_pmd, src_pmdval) ||
+		     !pmd_same(*dst_pmd, dst_pmdval))) {
+		err = -EAGAIN;
+		goto unlock_ptls;
+	}
+	if (folio_maybe_dma_pinned(src_folio) ||
+	    !PageAnonExclusive(&src_folio->page)) {
+		err = -EBUSY;
+		goto unlock_ptls;
+	}
+
+	if (WARN_ON_ONCE(!folio_test_head(src_folio)) ||
+	    WARN_ON_ONCE(!folio_test_anon(src_folio))) {
+		err = -EBUSY;
+		goto unlock_ptls;
+	}
+
+	folio_move_anon_rmap(src_folio, dst_vma);
+	WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
+
+	src_pmdval = pmdp_huge_clear_flush(src_vma, src_addr, src_pmd);
+	/* Folio got pinned from under us. Put it back and fail the move. */
+	if (folio_maybe_dma_pinned(src_folio)) {
+		set_pmd_at(mm, src_addr, src_pmd, src_pmdval);
+		err = -EBUSY;
+		goto unlock_ptls;
+	}
+
+	_dst_pmd = mk_huge_pmd(&src_folio->page, dst_vma->vm_page_prot);
+	/* Follow mremap() behavior and treat the entry dirty after the move */
+	_dst_pmd = pmd_mkwrite(pmd_mkdirty(_dst_pmd), dst_vma);
+	set_pmd_at(mm, dst_addr, dst_pmd, _dst_pmd);
+
+	src_pgtable = pgtable_trans_huge_withdraw(mm, src_pmd);
+	pgtable_trans_huge_deposit(mm, dst_pmd, src_pgtable);
+unlock_ptls:
+	double_pt_unlock(src_ptl, dst_ptl);
+	anon_vma_unlock_write(src_anon_vma);
+	put_anon_vma(src_anon_vma);
+unlock_folio:
+	/* unblock rmap walks */
+	folio_unlock(src_folio);
+	mmu_notifier_invalidate_range_end(&range);
+	folio_put(src_folio);
+	return err;
+}
+#endif /* CONFIG_USERFAULTFD */
+
 /*
  * Returns page table lock pointer if a given pmd maps a thp, NULL otherwise.
  *
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index bc2d8ff269c7..b800e511893b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1139,6 +1139,9 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
 	 * Prevent all access to pagetables with the exception of
 	 * gup_fast later handled by the ptep_clear_flush and the VM
 	 * handled by the anon_vma lock + PG_lock.
+	 *
+	 * UFFDIO_MOVE is prevented to race as well thanks to the
+	 * mmap_lock.
 	 */
 	mmap_write_lock(mm);
 	result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
diff --git a/mm/rmap.c b/mm/rmap.c
index 525c5bc0b0b3..de9426ad0f1b 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -490,6 +490,12 @@ void __init anon_vma_init(void)
  * 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.
+ *
+ * NOTE: the caller should normally hold folio lock when calling this.  If
+ * not, the caller needs to double check the anon_vma didn't change after
+ * taking the anon_vma lock for either read or write (UFFDIO_MOVE can modify it
+ * concurrently without folio lock protection). See folio_lock_anon_vma_read()
+ * which has already covered that, and comment above remap_pages().
  */
 struct anon_vma *folio_get_anon_vma(struct folio *folio)
 {
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 96d9eae5c7cc..c8a836b5dead 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -842,3 +842,599 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
 	mmap_read_unlock(dst_mm);
 	return err;
 }
+
+
+void double_pt_lock(spinlock_t *ptl1,
+		    spinlock_t *ptl2)
+	__acquires(ptl1)
+	__acquires(ptl2)
+{
+	spinlock_t *ptl_tmp;
+
+	if (ptl1 > ptl2) {
+		/* exchange ptl1 and ptl2 */
+		ptl_tmp = ptl1;
+		ptl1 = ptl2;
+		ptl2 = ptl_tmp;
+	}
+	/* lock in virtual address order to avoid lock inversion */
+	spin_lock(ptl1);
+	if (ptl1 != ptl2)
+		spin_lock_nested(ptl2, SINGLE_DEPTH_NESTING);
+	else
+		__acquire(ptl2);
+}
+
+void double_pt_unlock(spinlock_t *ptl1,
+		      spinlock_t *ptl2)
+	__releases(ptl1)
+	__releases(ptl2)
+{
+	spin_unlock(ptl1);
+	if (ptl1 != ptl2)
+		spin_unlock(ptl2);
+	else
+		__release(ptl2);
+}
+
+
+static int move_present_pte(struct mm_struct *mm,
+			    struct vm_area_struct *dst_vma,
+			    struct vm_area_struct *src_vma,
+			    unsigned long dst_addr, unsigned long src_addr,
+			    pte_t *dst_pte, pte_t *src_pte,
+			    pte_t orig_dst_pte, pte_t orig_src_pte,
+			    spinlock_t *dst_ptl, spinlock_t *src_ptl,
+			    struct folio *src_folio)
+{
+	int err = 0;
+
+	double_pt_lock(dst_ptl, src_ptl);
+
+	if (!pte_same(*src_pte, orig_src_pte) ||
+	    !pte_same(*dst_pte, orig_dst_pte)) {
+		err = -EAGAIN;
+		goto out;
+	}
+	if (folio_test_large(src_folio) ||
+	    folio_maybe_dma_pinned(src_folio) ||
+	    !PageAnonExclusive(&src_folio->page)) {
+		err = -EBUSY;
+		goto out;
+	}
+
+	folio_move_anon_rmap(src_folio, dst_vma);
+	WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
+
+	orig_src_pte = ptep_clear_flush(src_vma, src_addr, src_pte);
+	/* Folio got pinned from under us. Put it back and fail the move. */
+	if (folio_maybe_dma_pinned(src_folio)) {
+		set_pte_at(mm, src_addr, src_pte, orig_src_pte);
+		err = -EBUSY;
+		goto out;
+	}
+
+	orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot);
+	/* Follow mremap() behavior and treat the entry dirty after the move */
+	orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma);
+
+	set_pte_at(mm, dst_addr, dst_pte, orig_dst_pte);
+out:
+	double_pt_unlock(dst_ptl, src_ptl);
+	return err;
+}
+
+static int move_swap_pte(struct mm_struct *mm,
+			 unsigned long dst_addr, unsigned long src_addr,
+			 pte_t *dst_pte, pte_t *src_pte,
+			 pte_t orig_dst_pte, pte_t orig_src_pte,
+			 spinlock_t *dst_ptl, spinlock_t *src_ptl)
+{
+	if (!pte_swp_exclusive(orig_src_pte))
+		return -EBUSY;
+
+	double_pt_lock(dst_ptl, src_ptl);
+
+	if (!pte_same(*src_pte, orig_src_pte) ||
+	    !pte_same(*dst_pte, orig_dst_pte)) {
+		double_pt_unlock(dst_ptl, src_ptl);
+		return -EAGAIN;
+	}
+
+	orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte);
+	set_pte_at(mm, dst_addr, dst_pte, orig_src_pte);
+	double_pt_unlock(dst_ptl, src_ptl);
+
+	return 0;
+}
+
+/*
+ * The mmap_lock for reading is held by the caller. Just move the page
+ * from src_pmd to dst_pmd if possible, and return true if succeeded
+ * in moving the page.
+ */
+static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,
+			  struct vm_area_struct *dst_vma,
+			  struct vm_area_struct *src_vma,
+			  unsigned long dst_addr, unsigned long src_addr,
+			  __u64 mode)
+{
+	swp_entry_t entry;
+	pte_t orig_src_pte, orig_dst_pte;
+	pte_t src_folio_pte;
+	spinlock_t *src_ptl, *dst_ptl;
+	pte_t *src_pte = NULL;
+	pte_t *dst_pte = NULL;
+
+	struct folio *src_folio = NULL;
+	struct anon_vma *src_anon_vma = NULL;
+	struct mmu_notifier_range range;
+	int err = 0;
+
+	flush_cache_range(src_vma, src_addr, src_addr + PAGE_SIZE);
+	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
+				src_addr, src_addr + PAGE_SIZE);
+	mmu_notifier_invalidate_range_start(&range);
+retry:
+	dst_pte = pte_offset_map_nolock(mm, dst_pmd, dst_addr, &dst_ptl);
+
+	/* Retry if a huge pmd materialized from under us */
+	if (unlikely(!dst_pte)) {
+		err = -EAGAIN;
+		goto out;
+	}
+
+	src_pte = pte_offset_map_nolock(mm, src_pmd, src_addr, &src_ptl);
+
+	/*
+	 * We held the mmap_lock for reading so MADV_DONTNEED
+	 * can zap transparent huge pages under us, or the
+	 * transparent huge page fault can establish new
+	 * transparent huge pages under us.
+	 */
+	if (unlikely(!src_pte)) {
+		err = -EAGAIN;
+		goto out;
+	}
+
+	/* Sanity checks before the operation */
+	if (WARN_ON_ONCE(pmd_none(*dst_pmd)) ||	WARN_ON_ONCE(pmd_none(*src_pmd)) ||
+	    WARN_ON_ONCE(pmd_trans_huge(*dst_pmd)) || WARN_ON_ONCE(pmd_trans_huge(*src_pmd))) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	spin_lock(dst_ptl);
+	orig_dst_pte = *dst_pte;
+	spin_unlock(dst_ptl);
+	if (!pte_none(orig_dst_pte)) {
+		err = -EEXIST;
+		goto out;
+	}
+
+	spin_lock(src_ptl);
+	orig_src_pte = *src_pte;
+	spin_unlock(src_ptl);
+	if (pte_none(orig_src_pte)) {
+		if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES))
+			err = -ENOENT;
+		else /* nothing to do to move a hole */
+			err = 0;
+		goto out;
+	}
+
+	/* If PTE changed after we locked the folio them start over */
+	if (src_folio && unlikely(!pte_same(src_folio_pte, orig_src_pte))) {
+		err = -EAGAIN;
+		goto out;
+	}
+
+	if (pte_present(orig_src_pte)) {
+		/*
+		 * Pin and lock both source folio and anon_vma. Since we are in
+		 * RCU read section, we can't block, so on contention have to
+		 * unmap the ptes, obtain the lock and retry.
+		 */
+		if (!src_folio) {
+			struct folio *folio;
+
+			/*
+			 * Pin the page while holding the lock to be sure the
+			 * page isn't freed under us
+			 */
+			spin_lock(src_ptl);
+			if (!pte_same(orig_src_pte, *src_pte)) {
+				spin_unlock(src_ptl);
+				err = -EAGAIN;
+				goto out;
+			}
+
+			folio = vm_normal_folio(src_vma, src_addr, orig_src_pte);
+			if (!folio || folio_test_large(folio) ||
+			    !PageAnonExclusive(&folio->page)) {
+				spin_unlock(src_ptl);
+				err = -EBUSY;
+				goto out;
+			}
+
+			folio_get(folio);
+			src_folio = folio;
+			src_folio_pte = orig_src_pte;
+			spin_unlock(src_ptl);
+
+			if (!folio_trylock(src_folio)) {
+				pte_unmap(&orig_src_pte);
+				pte_unmap(&orig_dst_pte);
+				src_pte = dst_pte = NULL;
+				/* now we can block and wait */
+				folio_lock(src_folio);
+				goto retry;
+			}
+
+			if (WARN_ON_ONCE(!folio_test_anon(src_folio))) {
+				err = -EBUSY;
+				goto out;
+			}
+		}
+
+		if (!src_anon_vma) {
+			/*
+			 * folio_referenced walks the anon_vma chain
+			 * without the folio lock. Serialize against it with
+			 * the anon_vma lock, the folio lock is not enough.
+			 */
+			src_anon_vma = folio_get_anon_vma(src_folio);
+			if (!src_anon_vma) {
+				/* page was unmapped from under us */
+				err = -EAGAIN;
+				goto out;
+			}
+			if (!anon_vma_trylock_write(src_anon_vma)) {
+				pte_unmap(&orig_src_pte);
+				pte_unmap(&orig_dst_pte);
+				src_pte = dst_pte = NULL;
+				/* now we can block and wait */
+				anon_vma_lock_write(src_anon_vma);
+				goto retry;
+			}
+		}
+
+		err = move_present_pte(mm,  dst_vma, src_vma,
+				       dst_addr, src_addr, dst_pte, src_pte,
+				       orig_dst_pte, orig_src_pte,
+				       dst_ptl, src_ptl, src_folio);
+	} else {
+		entry = pte_to_swp_entry(orig_src_pte);
+		if (non_swap_entry(entry)) {
+			if (is_migration_entry(entry)) {
+				pte_unmap(&orig_src_pte);
+				pte_unmap(&orig_dst_pte);
+				src_pte = dst_pte = NULL;
+				migration_entry_wait(mm, src_pmd, src_addr);
+				err = -EAGAIN;
+			} else
+				err = -EFAULT;
+			goto out;
+		}
+
+		err = move_swap_pte(mm, dst_addr, src_addr,
+				    dst_pte, src_pte,
+				    orig_dst_pte, orig_src_pte,
+				    dst_ptl, src_ptl);
+	}
+
+out:
+	if (src_anon_vma) {
+		anon_vma_unlock_write(src_anon_vma);
+		put_anon_vma(src_anon_vma);
+	}
+	if (src_folio) {
+		folio_unlock(src_folio);
+		folio_put(src_folio);
+	}
+	if (dst_pte)
+		pte_unmap(dst_pte);
+	if (src_pte)
+		pte_unmap(src_pte);
+	mmu_notifier_invalidate_range_end(&range);
+
+	return err;
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline bool move_splits_huge_pmd(unsigned long dst_addr,
+					unsigned long src_addr,
+					unsigned long src_end)
+{
+	return (src_addr & ~HPAGE_PMD_MASK) || (dst_addr & ~HPAGE_PMD_MASK) ||
+		src_end - src_addr < HPAGE_PMD_SIZE;
+}
+#else
+static inline bool move_splits_huge_pmd(unsigned long dst_addr,
+					unsigned long src_addr,
+					unsigned long src_end)
+{
+	/* This is unreachable anyway, just to avoid warnings when HPAGE_PMD_SIZE==0 */
+	return false;
+}
+#endif
+
+static inline bool vma_move_compatible(struct vm_area_struct *vma)
+{
+	return !(vma->vm_flags & (VM_PFNMAP | VM_IO |  VM_HUGETLB |
+				  VM_MIXEDMAP | VM_SHADOW_STACK));
+}
+
+static int validate_move_areas(struct userfaultfd_ctx *ctx,
+			       struct vm_area_struct *src_vma,
+			       struct vm_area_struct *dst_vma)
+{
+	/* Only allow moving if both have the same access and protection */
+	if ((src_vma->vm_flags & VM_ACCESS_FLAGS) != (dst_vma->vm_flags & VM_ACCESS_FLAGS) ||
+	    pgprot_val(src_vma->vm_page_prot) != pgprot_val(dst_vma->vm_page_prot))
+		return -EINVAL;
+
+	/* Only allow moving if both are mlocked or both aren't */
+	if ((src_vma->vm_flags & VM_LOCKED) != (dst_vma->vm_flags & VM_LOCKED))
+		return -EINVAL;
+
+	/*
+	 * For now, we keep it simple and only move between writable VMAs.
+	 * Access flags are equal, therefore cheching only the source is enough.
+	 */
+	if (!(src_vma->vm_flags & VM_WRITE))
+		return -EINVAL;
+
+	/* Check if vma flags indicate content which can be moved */
+	if (!vma_move_compatible(src_vma) || !vma_move_compatible(dst_vma))
+		return -EINVAL;
+
+	/* Ensure dst_vma is registered in uffd we are operating on */
+	if (!dst_vma->vm_userfaultfd_ctx.ctx ||
+	    dst_vma->vm_userfaultfd_ctx.ctx != ctx)
+		return -EINVAL;
+
+	/* Only allow moving across anonymous vmas */
+	if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma))
+		return -EINVAL;
+
+	/*
+	 * Ensure the dst_vma has a anon_vma or this page
+	 * would get a NULL anon_vma when moved in the
+	 * dst_vma.
+	 */
+	if (unlikely(anon_vma_prepare(dst_vma)))
+		return -ENOMEM;
+
+	return 0;
+}
+
+/**
+ * move_pages - move arbitrary anonymous pages of an existing vma
+ * @dst_start: start of the destination virtual memory range
+ * @src_start: start of the source virtual memory range
+ * @len: length of the virtual memory range
+ *
+ * Must be called with mmap_lock held for read.
+ *
+ * move_pages() remaps arbitrary anonymous pages atomically in zero
+ * copy. It only works on non shared anonymous pages because those can
+ * be relocated without generating non linear anon_vmas in the rmap
+ * code.
+ *
+ * It provides a zero copy mechanism to handle userspace page faults.
+ * The source vma pages should have mapcount == 1, which can be
+ * enforced by using madvise(MADV_DONTFORK) on src vma.
+ *
+ * The thread receiving the page during the userland page fault
+ * will receive the faulting page in the source vma through the network,
+ * storage or any other I/O device (MADV_DONTFORK in the source vma
+ * avoids move_pages() to fail with -EBUSY if the process forks before
+ * move_pages() is called), then it will call move_pages() to map the
+ * page in the faulting address in the destination vma.
+ *
+ * This userfaultfd command works purely via pagetables, so it's the
+ * most efficient way to move physical non shared anonymous pages
+ * across different virtual addresses. Unlike mremap()/mmap()/munmap()
+ * it does not create any new vmas. The mapping in the destination
+ * address is atomic.
+ *
+ * It only works if the vma protection bits are identical from the
+ * source and destination vma.
+ *
+ * It can remap non shared anonymous pages within the same vma too.
+ *
+ * If the source virtual memory range has any unmapped holes, or if
+ * the destination virtual memory range is not a whole unmapped hole,
+ * move_pages() will fail respectively with -ENOENT or -EEXIST. This
+ * provides a very strict behavior to avoid any chance of memory
+ * corruption going unnoticed if there are userland race conditions.
+ * Only one thread should resolve the userland page fault at any given
+ * time for any given faulting address. This means that if two threads
+ * try to both call move_pages() on the same destination address at the
+ * same time, the second thread will get an explicit error from this
+ * command.
+ *
+ * The command retval will return "len" is successful. The command
+ * however can be interrupted by fatal signals or errors. If
+ * interrupted it will return the number of bytes successfully
+ * remapped before the interruption if any, or the negative error if
+ * none. It will never return zero. Either it will return an error or
+ * an amount of bytes successfully moved. If the retval reports a
+ * "short" remap, the move_pages() command should be repeated by
+ * userland with src+retval, dst+reval, len-retval if it wants to know
+ * about the error that interrupted it.
+ *
+ * The UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES flag can be specified to
+ * prevent -ENOENT errors to materialize if there are holes in the
+ * source virtual range that is being remapped. The holes will be
+ * accounted as successfully remapped in the retval of the
+ * command. This is mostly useful to remap hugepage naturally aligned
+ * virtual regions without knowing if there are transparent hugepage
+ * in the regions or not, but preventing the risk of having to split
+ * the hugepmd during the remap.
+ *
+ * If there's any rmap walk that is taking the anon_vma locks without
+ * first obtaining the folio lock (the only current instance is
+ * folio_referenced), they will have to verify if the folio->mapping
+ * has changed after taking the anon_vma lock. If it changed they
+ * should release the lock and retry obtaining a new anon_vma, because
+ * it means the anon_vma was changed by move_pages() before the lock
+ * could be obtained. This is the only additional complexity added to
+ * the rmap code to provide this anonymous page remapping functionality.
+ */
+ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
+		   unsigned long dst_start, unsigned long src_start,
+		   unsigned long len, __u64 mode)
+{
+	struct vm_area_struct *src_vma, *dst_vma;
+	unsigned long src_addr, dst_addr;
+	pmd_t *src_pmd, *dst_pmd;
+	long err = -EINVAL;
+	ssize_t moved = 0;
+
+	/* Sanitize the command parameters. */
+	if (WARN_ON_ONCE(src_start & ~PAGE_MASK) ||
+	    WARN_ON_ONCE(dst_start & ~PAGE_MASK) ||
+	    WARN_ON_ONCE(len & ~PAGE_MASK))
+		goto out;
+
+	/* Does the address range wrap, or is the span zero-sized? */
+	if (WARN_ON_ONCE(src_start + len <= src_start) ||
+	    WARN_ON_ONCE(dst_start + len <= dst_start))
+		goto out;
+
+	/*
+	 * Make sure the vma is not shared, that the src and dst remap
+	 * ranges are both valid and fully within a single existing
+	 * vma.
+	 */
+	src_vma = find_vma(mm, src_start);
+	if (!src_vma || (src_vma->vm_flags & VM_SHARED))
+		goto out;
+	if (src_start < src_vma->vm_start ||
+	    src_start + len > src_vma->vm_end)
+		goto out;
+
+	dst_vma = find_vma(mm, dst_start);
+	if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
+		goto out;
+	if (dst_start < dst_vma->vm_start ||
+	    dst_start + len > dst_vma->vm_end)
+		goto out;
+
+	err = validate_move_areas(ctx, src_vma, dst_vma);
+	if (err)
+		goto out;
+
+	for (src_addr = src_start, dst_addr = dst_start;
+	     src_addr < src_start + len;) {
+		spinlock_t *ptl;
+		pmd_t dst_pmdval;
+		unsigned long step_size;
+
+		/*
+		 * Below works because anonymous area would not have a
+		 * transparent huge PUD. If file-backed support is added,
+		 * that case would need to be handled here.
+		 */
+		src_pmd = mm_find_pmd(mm, src_addr);
+		if (unlikely(!src_pmd)) {
+			if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) {
+				err = -ENOENT;
+				break;
+			}
+			src_pmd = mm_alloc_pmd(mm, src_addr);
+			if (unlikely(!src_pmd)) {
+				err = -ENOMEM;
+				break;
+			}
+		}
+		dst_pmd = mm_alloc_pmd(mm, dst_addr);
+		if (unlikely(!dst_pmd)) {
+			err = -ENOMEM;
+			break;
+		}
+
+		dst_pmdval = pmdp_get_lockless(dst_pmd);
+		/*
+		 * If the dst_pmd is mapped as THP don't override it and just
+		 * be strict. If dst_pmd changes into TPH after this check, the
+		 * move_pages_huge_pmd() will detect the change and retry
+		 * while move_pages_pte() will detect the change and fail.
+		 */
+		if (unlikely(pmd_trans_huge(dst_pmdval))) {
+			err = -EEXIST;
+			break;
+		}
+
+		ptl = pmd_trans_huge_lock(src_pmd, src_vma);
+		if (ptl) {
+			if (pmd_devmap(*src_pmd)) {
+				spin_unlock(ptl);
+				err = -ENOENT;
+				break;
+			}
+
+			/* Check if we can move the pmd without splitting it. */
+			if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
+			    !pmd_none(dst_pmdval)) {
+				spin_unlock(ptl);
+				split_huge_pmd(src_vma, src_pmd, src_addr);
+				continue;
+			}
+
+			err = move_pages_huge_pmd(mm, dst_pmd, src_pmd,
+						  dst_pmdval, dst_vma, src_vma,
+						  dst_addr, src_addr);
+			step_size = HPAGE_PMD_SIZE;
+		} else {
+			if (pmd_none(*src_pmd)) {
+				if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) {
+					err = -ENOENT;
+					break;
+				}
+				if (unlikely(__pte_alloc(mm, src_pmd))) {
+					err = -ENOMEM;
+					break;
+				}
+			}
+
+			if (unlikely(pte_alloc(mm, dst_pmd))) {
+				err = -ENOMEM;
+				break;
+			}
+
+			err = move_pages_pte(mm, dst_pmd, src_pmd,
+					     dst_vma, src_vma,
+					     dst_addr, src_addr, mode);
+			step_size = PAGE_SIZE;
+		}
+
+		cond_resched();
+
+		if (fatal_signal_pending(current)) {
+			/* Do not override an error */
+			if (!err || err == -EAGAIN)
+				err = -EINTR;
+			break;
+		}
+
+		if (err) {
+			if (err == -EAGAIN)
+				continue;
+			break;
+		}
+
+		/* Proceed to the next page */
+		dst_addr += step_size;
+		src_addr += step_size;
+		moved += step_size;
+	}
+
+out:
+	VM_WARN_ON(moved < 0);
+	VM_WARN_ON(err > 0);
+	VM_WARN_ON(!moved && !err);
+	return moved ? moved : err;
+}
