mm: move internal core VMA manipulation functions to own file

This patch introduces vma.c and moves internal core VMA manipulation
functions to this file from mmap.c.

This allows us to isolate VMA functionality in a single place such that we
can create userspace testing code that invokes this functionality in an
environment where we can implement simple unit tests of core
functionality.

This patch ensures that core VMA functionality is explicitly marked as
such by its presence in mm/vma.h.

It also places the header includes required by vma.c in vma_internal.h,
which is simply imported by vma.c.  This makes the VMA functionality
testable, as userland testing code can simply stub out functionality as
required.

Link: https://lkml.kernel.org/r/c77a6aafb4c42aaadb8e7271a853658cbdca2e22.1722251717.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Gow <davidgow@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Kees Cook <kees@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Rae Moar <rmoar@google.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Pengfei Xu <pengfei.xu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 1766 insertions, 0 deletions

diff --git a/mm/vma.c b/mm/vma.c
new file mode 100644
index 000000000000..bf0546fe6eab
--- /dev/null
+++ b/mm/vma.c
@@ -0,0 +1,1766 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/*
+ * VMA-specific functions.
+ */
+
+#include "vma_internal.h"
+#include "vma.h"
+
+/*
+ * If the vma has a ->close operation then the driver probably needs to release
+ * per-vma resources, so we don't attempt to merge those if the caller indicates
+ * the current vma may be removed as part of the merge.
+ */
+static inline bool is_mergeable_vma(struct vm_area_struct *vma,
+		struct file *file, unsigned long vm_flags,
+		struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
+		struct anon_vma_name *anon_name, bool may_remove_vma)
+{
+	/*
+	 * VM_SOFTDIRTY should not prevent from VMA merging, if we
+	 * match the flags but dirty bit -- the caller should mark
+	 * merged VMA as dirty. If dirty bit won't be excluded from
+	 * comparison, we increase pressure on the memory system forcing
+	 * the kernel to generate new VMAs when old one could be
+	 * extended instead.
+	 */
+	if ((vma->vm_flags ^ vm_flags) & ~VM_SOFTDIRTY)
+		return false;
+	if (vma->vm_file != file)
+		return false;
+	if (may_remove_vma && vma->vm_ops && vma->vm_ops->close)
+		return false;
+	if (!is_mergeable_vm_userfaultfd_ctx(vma, vm_userfaultfd_ctx))
+		return false;
+	if (!anon_vma_name_eq(anon_vma_name(vma), anon_name))
+		return false;
+	return true;
+}
+
+static inline bool is_mergeable_anon_vma(struct anon_vma *anon_vma1,
+		 struct anon_vma *anon_vma2, struct vm_area_struct *vma)
+{
+	/*
+	 * The list_is_singular() test is to avoid merging VMA cloned from
+	 * parents. This can improve scalability caused by anon_vma lock.
+	 */
+	if ((!anon_vma1 || !anon_vma2) && (!vma ||
+		list_is_singular(&vma->anon_vma_chain)))
+		return true;
+	return anon_vma1 == anon_vma2;
+}
+
+/*
+ * init_multi_vma_prep() - Initializer for struct vma_prepare
+ * @vp: The vma_prepare struct
+ * @vma: The vma that will be altered once locked
+ * @next: The next vma if it is to be adjusted
+ * @remove: The first vma to be removed
+ * @remove2: The second vma to be removed
+ */
+static void init_multi_vma_prep(struct vma_prepare *vp,
+				struct vm_area_struct *vma,
+				struct vm_area_struct *next,
+				struct vm_area_struct *remove,
+				struct vm_area_struct *remove2)
+{
+	memset(vp, 0, sizeof(struct vma_prepare));
+	vp->vma = vma;
+	vp->anon_vma = vma->anon_vma;
+	vp->remove = remove;
+	vp->remove2 = remove2;
+	vp->adj_next = next;
+	if (!vp->anon_vma && next)
+		vp->anon_vma = next->anon_vma;
+
+	vp->file = vma->vm_file;
+	if (vp->file)
+		vp->mapping = vma->vm_file->f_mapping;
+
+}
+
+/*
+ * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
+ * in front of (at a lower virtual address and file offset than) the vma.
+ *
+ * We cannot merge two vmas if they have differently assigned (non-NULL)
+ * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
+ *
+ * We don't check here for the merged mmap wrapping around the end of pagecache
+ * indices (16TB on ia32) because do_mmap() does not permit mmap's which
+ * wrap, nor mmaps which cover the final page at index -1UL.
+ *
+ * We assume the vma may be removed as part of the merge.
+ */
+bool
+can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
+		struct anon_vma *anon_vma, struct file *file,
+		pgoff_t vm_pgoff, struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
+		struct anon_vma_name *anon_name)
+{
+	if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name, true) &&
+	    is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
+		if (vma->vm_pgoff == vm_pgoff)
+			return true;
+	}
+	return false;
+}
+
+/*
+ * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
+ * beyond (at a higher virtual address and file offset than) the vma.
+ *
+ * We cannot merge two vmas if they have differently assigned (non-NULL)
+ * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
+ *
+ * We assume that vma is not removed as part of the merge.
+ */
+bool
+can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
+		struct anon_vma *anon_vma, struct file *file,
+		pgoff_t vm_pgoff, struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
+		struct anon_vma_name *anon_name)
+{
+	if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name, false) &&
+	    is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
+		pgoff_t vm_pglen;
+
+		vm_pglen = vma_pages(vma);
+		if (vma->vm_pgoff + vm_pglen == vm_pgoff)
+			return true;
+	}
+	return false;
+}
+
+/*
+ * Close a vm structure and free it.
+ */
+void remove_vma(struct vm_area_struct *vma, bool unreachable)
+{
+	might_sleep();
+	if (vma->vm_ops && vma->vm_ops->close)
+		vma->vm_ops->close(vma);
+	if (vma->vm_file)
+		fput(vma->vm_file);
+	mpol_put(vma_policy(vma));
+	if (unreachable)
+		__vm_area_free(vma);
+	else
+		vm_area_free(vma);
+}
+
+/*
+ * Get rid of page table information in the indicated region.
+ *
+ * Called with the mm semaphore held.
+ */
+void unmap_region(struct mm_struct *mm, struct ma_state *mas,
+		struct vm_area_struct *vma, struct vm_area_struct *prev,
+		struct vm_area_struct *next, unsigned long start,
+		unsigned long end, unsigned long tree_end, bool mm_wr_locked)
+{
+	struct mmu_gather tlb;
+	unsigned long mt_start = mas->index;
+
+	lru_add_drain();
+	tlb_gather_mmu(&tlb, mm);
+	update_hiwater_rss(mm);
+	unmap_vmas(&tlb, mas, vma, start, end, tree_end, mm_wr_locked);
+	mas_set(mas, mt_start);
+	free_pgtables(&tlb, mas, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
+				 next ? next->vm_start : USER_PGTABLES_CEILING,
+				 mm_wr_locked);
+	tlb_finish_mmu(&tlb);
+}
+
+/*
+ * __split_vma() bypasses sysctl_max_map_count checking.  We use this where it
+ * has already been checked or doesn't make sense to fail.
+ * VMA Iterator will point to the end VMA.
+ */
+static int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
+		       unsigned long addr, int new_below)
+{
+	struct vma_prepare vp;
+	struct vm_area_struct *new;
+	int err;
+
+	WARN_ON(vma->vm_start >= addr);
+	WARN_ON(vma->vm_end <= addr);
+
+	if (vma->vm_ops && vma->vm_ops->may_split) {
+		err = vma->vm_ops->may_split(vma, addr);
+		if (err)
+			return err;
+	}
+
+	new = vm_area_dup(vma);
+	if (!new)
+		return -ENOMEM;
+
+	if (new_below) {
+		new->vm_end = addr;
+	} else {
+		new->vm_start = addr;
+		new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
+	}
+
+	err = -ENOMEM;
+	vma_iter_config(vmi, new->vm_start, new->vm_end);
+	if (vma_iter_prealloc(vmi, new))
+		goto out_free_vma;
+
+	err = vma_dup_policy(vma, new);
+	if (err)
+		goto out_free_vmi;
+
+	err = anon_vma_clone(new, vma);
+	if (err)
+		goto out_free_mpol;
+
+	if (new->vm_file)
+		get_file(new->vm_file);
+
+	if (new->vm_ops && new->vm_ops->open)
+		new->vm_ops->open(new);
+
+	vma_start_write(vma);
+	vma_start_write(new);
+
+	init_vma_prep(&vp, vma);
+	vp.insert = new;
+	vma_prepare(&vp);
+	vma_adjust_trans_huge(vma, vma->vm_start, addr, 0);
+
+	if (new_below) {
+		vma->vm_start = addr;
+		vma->vm_pgoff += (addr - new->vm_start) >> PAGE_SHIFT;
+	} else {
+		vma->vm_end = addr;
+	}
+
+	/* vma_complete stores the new vma */
+	vma_complete(&vp, vmi, vma->vm_mm);
+
+	/* Success. */
+	if (new_below)
+		vma_next(vmi);
+	return 0;
+
+out_free_mpol:
+	mpol_put(vma_policy(new));
+out_free_vmi:
+	vma_iter_free(vmi);
+out_free_vma:
+	vm_area_free(new);
+	return err;
+}
+
+/*
+ * Split a vma into two pieces at address 'addr', a new vma is allocated
+ * either for the first part or the tail.
+ */
+static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
+		     unsigned long addr, int new_below)
+{
+	if (vma->vm_mm->map_count >= sysctl_max_map_count)
+		return -ENOMEM;
+
+	return __split_vma(vmi, vma, addr, new_below);
+}
+
+/*
+ * Ok - we have the memory areas we should free on a maple tree so release them,
+ * and do the vma updates.
+ *
+ * Called with the mm semaphore held.
+ */
+static inline void remove_mt(struct mm_struct *mm, struct ma_state *mas)
+{
+	unsigned long nr_accounted = 0;
+	struct vm_area_struct *vma;
+
+	/* Update high watermark before we lower total_vm */
+	update_hiwater_vm(mm);
+	mas_for_each(mas, vma, ULONG_MAX) {
+		long nrpages = vma_pages(vma);
+
+		if (vma->vm_flags & VM_ACCOUNT)
+			nr_accounted += nrpages;
+		vm_stat_account(mm, vma->vm_flags, -nrpages);
+		remove_vma(vma, false);
+	}
+	vm_unacct_memory(nr_accounted);
+}
+
+/*
+ * init_vma_prep() - Initializer wrapper for vma_prepare struct
+ * @vp: The vma_prepare struct
+ * @vma: The vma that will be altered once locked
+ */
+void init_vma_prep(struct vma_prepare *vp,
+		   struct vm_area_struct *vma)
+{
+	init_multi_vma_prep(vp, vma, NULL, NULL, NULL);
+}
+
+/*
+ * Requires inode->i_mapping->i_mmap_rwsem
+ */
+static void __remove_shared_vm_struct(struct vm_area_struct *vma,
+				      struct address_space *mapping)
+{
+	if (vma_is_shared_maywrite(vma))
+		mapping_unmap_writable(mapping);
+
+	flush_dcache_mmap_lock(mapping);
+	vma_interval_tree_remove(vma, &mapping->i_mmap);
+	flush_dcache_mmap_unlock(mapping);
+}
+
+/*
+ * vma has some anon_vma assigned, and is already inserted on that
+ * anon_vma's interval trees.
+ *
+ * Before updating the vma's vm_start / vm_end / vm_pgoff fields, the
+ * vma must be removed from the anon_vma's interval trees using
+ * anon_vma_interval_tree_pre_update_vma().
+ *
+ * After the update, the vma will be reinserted using
+ * anon_vma_interval_tree_post_update_vma().
+ *
+ * The entire update must be protected by exclusive mmap_lock and by
+ * the root anon_vma's mutex.
+ */
+void
+anon_vma_interval_tree_pre_update_vma(struct vm_area_struct *vma)
+{
+	struct anon_vma_chain *avc;
+
+	list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
+		anon_vma_interval_tree_remove(avc, &avc->anon_vma->rb_root);
+}
+
+void
+anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma)
+{
+	struct anon_vma_chain *avc;
+
+	list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
+		anon_vma_interval_tree_insert(avc, &avc->anon_vma->rb_root);
+}
+
+static void __vma_link_file(struct vm_area_struct *vma,
+			    struct address_space *mapping)
+{
+	if (vma_is_shared_maywrite(vma))
+		mapping_allow_writable(mapping);
+
+	flush_dcache_mmap_lock(mapping);
+	vma_interval_tree_insert(vma, &mapping->i_mmap);
+	flush_dcache_mmap_unlock(mapping);
+}
+
+/*
+ * vma_prepare() - Helper function for handling locking VMAs prior to altering
+ * @vp: The initialized vma_prepare struct
+ */
+void vma_prepare(struct vma_prepare *vp)
+{
+	if (vp->file) {
+		uprobe_munmap(vp->vma, vp->vma->vm_start, vp->vma->vm_end);
+
+		if (vp->adj_next)
+			uprobe_munmap(vp->adj_next, vp->adj_next->vm_start,
+				      vp->adj_next->vm_end);
+
+		i_mmap_lock_write(vp->mapping);
+		if (vp->insert && vp->insert->vm_file) {
+			/*
+			 * Put into interval tree now, so instantiated pages
+			 * are visible to arm/parisc __flush_dcache_page
+			 * throughout; but we cannot insert into address
+			 * space until vma start or end is updated.
+			 */
+			__vma_link_file(vp->insert,
+					vp->insert->vm_file->f_mapping);
+		}
+	}
+
+	if (vp->anon_vma) {
+		anon_vma_lock_write(vp->anon_vma);
+		anon_vma_interval_tree_pre_update_vma(vp->vma);
+		if (vp->adj_next)
+			anon_vma_interval_tree_pre_update_vma(vp->adj_next);
+	}
+
+	if (vp->file) {
+		flush_dcache_mmap_lock(vp->mapping);
+		vma_interval_tree_remove(vp->vma, &vp->mapping->i_mmap);
+		if (vp->adj_next)
+			vma_interval_tree_remove(vp->adj_next,
+						 &vp->mapping->i_mmap);
+	}
+
+}
+
+/*
+ * dup_anon_vma() - Helper function to duplicate anon_vma
+ * @dst: The destination VMA
+ * @src: The source VMA
+ * @dup: Pointer to the destination VMA when successful.
+ *
+ * Returns: 0 on success.
+ */
+static int dup_anon_vma(struct vm_area_struct *dst,
+			struct vm_area_struct *src, struct vm_area_struct **dup)
+{
+	/*
+	 * Easily overlooked: when mprotect shifts the boundary, make sure the
+	 * expanding vma has anon_vma set if the shrinking vma had, to cover any
+	 * anon pages imported.
+	 */
+	if (src->anon_vma && !dst->anon_vma) {
+		int ret;
+
+		vma_assert_write_locked(dst);
+		dst->anon_vma = src->anon_vma;
+		ret = anon_vma_clone(dst, src);
+		if (ret)
+			return ret;
+
+		*dup = dst;
+	}
+
+	return 0;
+}
+
+#ifdef CONFIG_DEBUG_VM_MAPLE_TREE
+void validate_mm(struct mm_struct *mm)
+{
+	int bug = 0;
+	int i = 0;
+	struct vm_area_struct *vma;
+	VMA_ITERATOR(vmi, mm, 0);
+
+	mt_validate(&mm->mm_mt);
+	for_each_vma(vmi, vma) {
+#ifdef CONFIG_DEBUG_VM_RB
+		struct anon_vma *anon_vma = vma->anon_vma;
+		struct anon_vma_chain *avc;
+#endif
+		unsigned long vmi_start, vmi_end;
+		bool warn = 0;
+
+		vmi_start = vma_iter_addr(&vmi);
+		vmi_end = vma_iter_end(&vmi);
+		if (VM_WARN_ON_ONCE_MM(vma->vm_end != vmi_end, mm))
+			warn = 1;
+
+		if (VM_WARN_ON_ONCE_MM(vma->vm_start != vmi_start, mm))
+			warn = 1;
+
+		if (warn) {
+			pr_emerg("issue in %s\n", current->comm);
+			dump_stack();
+			dump_vma(vma);
+			pr_emerg("tree range: %px start %lx end %lx\n", vma,
+				 vmi_start, vmi_end - 1);
+			vma_iter_dump_tree(&vmi);
+		}
+
+#ifdef CONFIG_DEBUG_VM_RB
+		if (anon_vma) {
+			anon_vma_lock_read(anon_vma);
+			list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
+				anon_vma_interval_tree_verify(avc);
+			anon_vma_unlock_read(anon_vma);
+		}
+#endif
+		i++;
+	}
+	if (i != mm->map_count) {
+		pr_emerg("map_count %d vma iterator %d\n", mm->map_count, i);
+		bug = 1;
+	}
+	VM_BUG_ON_MM(bug, mm);
+}
+#endif /* CONFIG_DEBUG_VM_MAPLE_TREE */
+
+/*
+ * vma_expand - Expand an existing VMA
+ *
+ * @vmi: The vma iterator
+ * @vma: The vma to expand
+ * @start: The start of the vma
+ * @end: The exclusive end of the vma
+ * @pgoff: The page offset of vma
+ * @next: The current of next vma.
+ *
+ * Expand @vma to @start and @end.  Can expand off the start and end.  Will
+ * expand over @next if it's different from @vma and @end == @next->vm_end.
+ * Checking if the @vma can expand and merge with @next needs to be handled by
+ * the caller.
+ *
+ * Returns: 0 on success
+ */
+int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
+	       unsigned long start, unsigned long end, pgoff_t pgoff,
+	       struct vm_area_struct *next)
+{
+	struct vm_area_struct *anon_dup = NULL;
+	bool remove_next = false;
+	struct vma_prepare vp;
+
+	vma_start_write(vma);
+	if (next && (vma != next) && (end == next->vm_end)) {
+		int ret;
+
+		remove_next = true;
+		vma_start_write(next);
+		ret = dup_anon_vma(vma, next, &anon_dup);
+		if (ret)
+			return ret;
+	}
+
+	init_multi_vma_prep(&vp, vma, NULL, remove_next ? next : NULL, NULL);
+	/* Not merging but overwriting any part of next is not handled. */
+	VM_WARN_ON(next && !vp.remove &&
+		  next != vma && end > next->vm_start);
+	/* Only handles expanding */
+	VM_WARN_ON(vma->vm_start < start || vma->vm_end > end);
+
+	/* Note: vma iterator must be pointing to 'start' */
+	vma_iter_config(vmi, start, end);
+	if (vma_iter_prealloc(vmi, vma))
+		goto nomem;
+
+	vma_prepare(&vp);
+	vma_adjust_trans_huge(vma, start, end, 0);
+	vma_set_range(vma, start, end, pgoff);
+	vma_iter_store(vmi, vma);
+
+	vma_complete(&vp, vmi, vma->vm_mm);
+	return 0;
+
+nomem:
+	if (anon_dup)
+		unlink_anon_vmas(anon_dup);
+	return -ENOMEM;
+}
+
+/*
+ * vma_shrink() - Reduce an existing VMAs memory area
+ * @vmi: The vma iterator
+ * @vma: The VMA to modify
+ * @start: The new start
+ * @end: The new end
+ *
+ * Returns: 0 on success, -ENOMEM otherwise
+ */
+int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
+	       unsigned long start, unsigned long end, pgoff_t pgoff)
+{
+	struct vma_prepare vp;
+
+	WARN_ON((vma->vm_start != start) && (vma->vm_end != end));
+
+	if (vma->vm_start < start)
+		vma_iter_config(vmi, vma->vm_start, start);
+	else
+		vma_iter_config(vmi, end, vma->vm_end);
+
+	if (vma_iter_prealloc(vmi, NULL))
+		return -ENOMEM;
+
+	vma_start_write(vma);
+
+	init_vma_prep(&vp, vma);
+	vma_prepare(&vp);
+	vma_adjust_trans_huge(vma, start, end, 0);
+
+	vma_iter_clear(vmi);
+	vma_set_range(vma, start, end, pgoff);
+	vma_complete(&vp, vmi, vma->vm_mm);
+	return 0;
+}
+
+/*
+ * vma_complete- Helper function for handling the unlocking after altering VMAs,
+ * or for inserting a VMA.
+ *
+ * @vp: The vma_prepare struct
+ * @vmi: The vma iterator
+ * @mm: The mm_struct
+ */
+void vma_complete(struct vma_prepare *vp,
+		  struct vma_iterator *vmi, struct mm_struct *mm)
+{
+	if (vp->file) {
+		if (vp->adj_next)
+			vma_interval_tree_insert(vp->adj_next,
+						 &vp->mapping->i_mmap);
+		vma_interval_tree_insert(vp->vma, &vp->mapping->i_mmap);
+		flush_dcache_mmap_unlock(vp->mapping);
+	}
+
+	if (vp->remove && vp->file) {
+		__remove_shared_vm_struct(vp->remove, vp->mapping);
+		if (vp->remove2)
+			__remove_shared_vm_struct(vp->remove2, vp->mapping);
+	} else if (vp->insert) {
+		/*
+		 * split_vma has split insert from vma, and needs
+		 * us to insert it before dropping the locks
+		 * (it may either follow vma or precede it).
+		 */
+		vma_iter_store(vmi, vp->insert);
+		mm->map_count++;
+	}
+
+	if (vp->anon_vma) {
+		anon_vma_interval_tree_post_update_vma(vp->vma);
+		if (vp->adj_next)
+			anon_vma_interval_tree_post_update_vma(vp->adj_next);
+		anon_vma_unlock_write(vp->anon_vma);
+	}
+
+	if (vp->file) {
+		i_mmap_unlock_write(vp->mapping);
+		uprobe_mmap(vp->vma);
+
+		if (vp->adj_next)
+			uprobe_mmap(vp->adj_next);
+	}
+
+	if (vp->remove) {
+again:
+		vma_mark_detached(vp->remove, true);
+		if (vp->file) {
+			uprobe_munmap(vp->remove, vp->remove->vm_start,
+				      vp->remove->vm_end);
+			fput(vp->file);
+		}
+		if (vp->remove->anon_vma)
+			anon_vma_merge(vp->vma, vp->remove);
+		mm->map_count--;
+		mpol_put(vma_policy(vp->remove));
+		if (!vp->remove2)
+			WARN_ON_ONCE(vp->vma->vm_end < vp->remove->vm_end);
+		vm_area_free(vp->remove);
+
+		/*
+		 * In mprotect's case 6 (see comments on vma_merge),
+		 * we are removing both mid and next vmas
+		 */
+		if (vp->remove2) {
+			vp->remove = vp->remove2;
+			vp->remove2 = NULL;
+			goto again;
+		}
+	}
+	if (vp->insert && vp->file)
+		uprobe_mmap(vp->insert);
+	validate_mm(mm);
+}
+
+/*
+ * do_vmi_align_munmap() - munmap the aligned region from @start to @end.
+ * @vmi: The vma iterator
+ * @vma: The starting vm_area_struct
+ * @mm: The mm_struct
+ * @start: The aligned start address to munmap.
+ * @end: The aligned end address to munmap.
+ * @uf: The userfaultfd list_head
+ * @unlock: Set to true to drop the mmap_lock.  unlocking only happens on
+ * success.
+ *
+ * Return: 0 on success and drops the lock if so directed, error and leaves the
+ * lock held otherwise.
+ */
+int
+do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
+		    struct mm_struct *mm, unsigned long start,
+		    unsigned long end, struct list_head *uf, bool unlock)
+{
+	struct vm_area_struct *prev, *next = NULL;
+	struct maple_tree mt_detach;
+	int count = 0;
+	int error = -ENOMEM;
+	unsigned long locked_vm = 0;
+	MA_STATE(mas_detach, &mt_detach, 0, 0);
+	mt_init_flags(&mt_detach, vmi->mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
+	mt_on_stack(mt_detach);
+
+	/*
+	 * If we need to split any vma, do it now to save pain later.
+	 *
+	 * Note: mremap's move_vma VM_ACCOUNT handling assumes a partially
+	 * unmapped vm_area_struct will remain in use: so lower split_vma
+	 * places tmp vma above, and higher split_vma places tmp vma below.
+	 */
+
+	/* Does it split the first one? */
+	if (start > vma->vm_start) {
+
+		/*
+		 * Make sure that map_count on return from munmap() will
+		 * not exceed its limit; but let map_count go just above
+		 * its limit temporarily, to help free resources as expected.
+		 */
+		if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
+			goto map_count_exceeded;
+
+		error = __split_vma(vmi, vma, start, 1);
+		if (error)
+			goto start_split_failed;
+	}
+
+	/*
+	 * Detach a range of VMAs from the mm. Using next as a temp variable as
+	 * it is always overwritten.
+	 */
+	next = vma;
+	do {
+		/* Does it split the end? */
+		if (next->vm_end > end) {
+			error = __split_vma(vmi, next, end, 0);
+			if (error)
+				goto end_split_failed;
+		}
+		vma_start_write(next);
+		mas_set(&mas_detach, count);
+		error = mas_store_gfp(&mas_detach, next, GFP_KERNEL);
+		if (error)
+			goto munmap_gather_failed;
+		vma_mark_detached(next, true);
+		if (next->vm_flags & VM_LOCKED)
+			locked_vm += vma_pages(next);
+
+		count++;
+		if (unlikely(uf)) {
+			/*
+			 * If userfaultfd_unmap_prep returns an error the vmas
+			 * will remain split, but userland will get a
+			 * highly unexpected error anyway. This is no
+			 * different than the case where the first of the two
+			 * __split_vma fails, but we don't undo the first
+			 * split, despite we could. This is unlikely enough
+			 * failure that it's not worth optimizing it for.
+			 */
+			error = userfaultfd_unmap_prep(next, start, end, uf);
+
+			if (error)
+				goto userfaultfd_error;
+		}
+#ifdef CONFIG_DEBUG_VM_MAPLE_TREE
+		BUG_ON(next->vm_start < start);
+		BUG_ON(next->vm_start > end);
+#endif
+	} for_each_vma_range(*vmi, next, end);
+
+#if defined(CONFIG_DEBUG_VM_MAPLE_TREE)
+	/* Make sure no VMAs are about to be lost. */
+	{
+		MA_STATE(test, &mt_detach, 0, 0);
+		struct vm_area_struct *vma_mas, *vma_test;
+		int test_count = 0;
+
+		vma_iter_set(vmi, start);
+		rcu_read_lock();
+		vma_test = mas_find(&test, count - 1);
+		for_each_vma_range(*vmi, vma_mas, end) {
+			BUG_ON(vma_mas != vma_test);
+			test_count++;
+			vma_test = mas_next(&test, count - 1);
+		}
+		rcu_read_unlock();
+		BUG_ON(count != test_count);
+	}
+#endif
+
+	while (vma_iter_addr(vmi) > start)
+		vma_iter_prev_range(vmi);
+
+	error = vma_iter_clear_gfp(vmi, start, end, GFP_KERNEL);
+	if (error)
+		goto clear_tree_failed;
+
+	/* Point of no return */
+	mm->locked_vm -= locked_vm;
+	mm->map_count -= count;
+	if (unlock)
+		mmap_write_downgrade(mm);
+
+	prev = vma_iter_prev_range(vmi);
+	next = vma_next(vmi);
+	if (next)
+		vma_iter_prev_range(vmi);
+
+	/*
+	 * We can free page tables without write-locking mmap_lock because VMAs
+	 * were isolated before we downgraded mmap_lock.
+	 */
+	mas_set(&mas_detach, 1);
+	unmap_region(mm, &mas_detach, vma, prev, next, start, end, count,
+		     !unlock);
+	/* Statistics and freeing VMAs */
+	mas_set(&mas_detach, 0);
+	remove_mt(mm, &mas_detach);
+	validate_mm(mm);
+	if (unlock)
+		mmap_read_unlock(mm);
+
+	__mt_destroy(&mt_detach);
+	return 0;
+
+clear_tree_failed:
+userfaultfd_error:
+munmap_gather_failed:
+end_split_failed:
+	mas_set(&mas_detach, 0);
+	mas_for_each(&mas_detach, next, end)
+		vma_mark_detached(next, false);
+
+	__mt_destroy(&mt_detach);
+start_split_failed:
+map_count_exceeded:
+	validate_mm(mm);
+	return error;
+}
+
+/*
+ * do_vmi_munmap() - munmap a given range.
+ * @vmi: The vma iterator
+ * @mm: The mm_struct
+ * @start: The start address to munmap
+ * @len: The length of the range to munmap
+ * @uf: The userfaultfd list_head
+ * @unlock: set to true if the user wants to drop the mmap_lock on success
+ *
+ * This function takes a @mas that is either pointing to the previous VMA or set
+ * to MA_START and sets it up to remove the mapping(s).  The @len will be
+ * aligned and any arch_unmap work will be preformed.
+ *
+ * Return: 0 on success and drops the lock if so directed, error and leaves the
+ * lock held otherwise.
+ */
+int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
+		  unsigned long start, size_t len, struct list_head *uf,
+		  bool unlock)
+{
+	unsigned long end;
+	struct vm_area_struct *vma;
+
+	if ((offset_in_page(start)) || start > TASK_SIZE || len > TASK_SIZE-start)
+		return -EINVAL;
+
+	end = start + PAGE_ALIGN(len);
+	if (end == start)
+		return -EINVAL;
+
+	/*
+	 * Check if memory is sealed before arch_unmap.
+	 * Prevent unmapping a sealed VMA.
+	 * can_modify_mm assumes we have acquired the lock on MM.
+	 */
+	if (unlikely(!can_modify_mm(mm, start, end)))
+		return -EPERM;
+
+	 /* arch_unmap() might do unmaps itself.  */
+	arch_unmap(mm, start, end);
+
+	/* Find the first overlapping VMA */
+	vma = vma_find(vmi, end);
+	if (!vma) {
+		if (unlock)
+			mmap_write_unlock(mm);
+		return 0;
+	}
+
+	return do_vmi_align_munmap(vmi, vma, mm, start, end, uf, unlock);
+}
+
+/*
+ * Given a mapping request (addr,end,vm_flags,file,pgoff,anon_name),
+ * figure out whether that can be merged with its predecessor or its
+ * successor.  Or both (it neatly fills a hole).
+ *
+ * In most cases - when called for mmap, brk or mremap - [addr,end) is
+ * certain not to be mapped by the time vma_merge is called; but when
+ * called for mprotect, it is certain to be already mapped (either at
+ * an offset within prev, or at the start of next), and the flags of
+ * this area are about to be changed to vm_flags - and the no-change
+ * case has already been eliminated.
+ *
+ * The following mprotect cases have to be considered, where **** is
+ * the area passed down from mprotect_fixup, never extending beyond one
+ * vma, PPPP is the previous vma, CCCC is a concurrent vma that starts
+ * at the same address as **** and is of the same or larger span, and
+ * NNNN the next vma after ****:
+ *
+ *     ****             ****                   ****
+ *    PPPPPPNNNNNN    PPPPPPNNNNNN       PPPPPPCCCCCC
+ *    cannot merge    might become       might become
+ *                    PPNNNNNNNNNN       PPPPPPPPPPCC
+ *    mmap, brk or    case 4 below       case 5 below
+ *    mremap move:
+ *                        ****               ****
+ *                    PPPP    NNNN       PPPPCCCCNNNN
+ *                    might become       might become
+ *                    PPPPPPPPPPPP 1 or  PPPPPPPPPPPP 6 or
+ *                    PPPPPPPPNNNN 2 or  PPPPPPPPNNNN 7 or
+ *                    PPPPNNNNNNNN 3     PPPPNNNNNNNN 8
+ *
+ * It is important for case 8 that the vma CCCC overlapping the
+ * region **** is never going to extended over NNNN. Instead NNNN must
+ * be extended in region **** and CCCC must be removed. This way in
+ * all cases where vma_merge succeeds, the moment vma_merge drops the
+ * rmap_locks, the properties of the merged vma will be already
+ * correct for the whole merged range. Some of those properties like
+ * vm_page_prot/vm_flags may be accessed by rmap_walks and they must
+ * be correct for the whole merged range immediately after the
+ * rmap_locks are released. Otherwise if NNNN would be removed and
+ * CCCC would be extended over the NNNN range, remove_migration_ptes
+ * or other rmap walkers (if working on addresses beyond the "end"
+ * parameter) may establish ptes with the wrong permissions of CCCC
+ * instead of the right permissions of NNNN.
+ *
+ * In the code below:
+ * PPPP is represented by *prev
+ * CCCC is represented by *curr or not represented at all (NULL)
+ * NNNN is represented by *next or not represented at all (NULL)
+ * **** is not represented - it will be merged and the vma containing the
+ *      area is returned, or the function will return NULL
+ */
+static struct vm_area_struct
+*vma_merge(struct vma_iterator *vmi, struct vm_area_struct *prev,
+	   struct vm_area_struct *src, unsigned long addr, unsigned long end,
+	   unsigned long vm_flags, pgoff_t pgoff, struct mempolicy *policy,
+	   struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
+	   struct anon_vma_name *anon_name)
+{
+	struct mm_struct *mm = src->vm_mm;
+	struct anon_vma *anon_vma = src->anon_vma;
+	struct file *file = src->vm_file;
+	struct vm_area_struct *curr, *next, *res;
+	struct vm_area_struct *vma, *adjust, *remove, *remove2;
+	struct vm_area_struct *anon_dup = NULL;
+	struct vma_prepare vp;
+	pgoff_t vma_pgoff;
+	int err = 0;
+	bool merge_prev = false;
+	bool merge_next = false;
+	bool vma_expanded = false;
+	unsigned long vma_start = addr;
+	unsigned long vma_end = end;
+	pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
+	long adj_start = 0;
+
+	/*
+	 * We later require that vma->vm_flags == vm_flags,
+	 * so this tests vma->vm_flags & VM_SPECIAL, too.
+	 */
+	if (vm_flags & VM_SPECIAL)
+		return NULL;
+
+	/* Does the input range span an existing VMA? (cases 5 - 8) */
+	curr = find_vma_intersection(mm, prev ? prev->vm_end : 0, end);
+
+	if (!curr ||			/* cases 1 - 4 */
+	    end == curr->vm_end)	/* cases 6 - 8, adjacent VMA */
+		next = vma_lookup(mm, end);
+	else
+		next = NULL;		/* case 5 */
+
+	if (prev) {
+		vma_start = prev->vm_start;
+		vma_pgoff = prev->vm_pgoff;
+
+		/* Can we merge the predecessor? */
+		if (addr == prev->vm_end && mpol_equal(vma_policy(prev), policy)
+		    && can_vma_merge_after(prev, vm_flags, anon_vma, file,
+					   pgoff, vm_userfaultfd_ctx, anon_name)) {
+			merge_prev = true;
+			vma_prev(vmi);
+		}
+	}
+
+	/* Can we merge the successor? */
+	if (next && mpol_equal(policy, vma_policy(next)) &&
+	    can_vma_merge_before(next, vm_flags, anon_vma, file, pgoff+pglen,
+				 vm_userfaultfd_ctx, anon_name)) {
+		merge_next = true;
+	}
+
+	/* Verify some invariant that must be enforced by the caller. */
+	VM_WARN_ON(prev && addr <= prev->vm_start);
+	VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end));
+	VM_WARN_ON(addr >= end);
+
+	if (!merge_prev && !merge_next)
+		return NULL; /* Not mergeable. */
+
+	if (merge_prev)
+		vma_start_write(prev);
+
+	res = vma = prev;
+	remove = remove2 = adjust = NULL;
+
+	/* Can we merge both the predecessor and the successor? */
+	if (merge_prev && merge_next &&
+	    is_mergeable_anon_vma(prev->anon_vma, next->anon_vma, NULL)) {
+		vma_start_write(next);
+		remove = next;				/* case 1 */
+		vma_end = next->vm_end;
+		err = dup_anon_vma(prev, next, &anon_dup);
+		if (curr) {				/* case 6 */
+			vma_start_write(curr);
+			remove = curr;
+			remove2 = next;
+			/*
+			 * Note that the dup_anon_vma below cannot overwrite err
+			 * since the first caller would do nothing unless next
+			 * has an anon_vma.
+			 */
+			if (!next->anon_vma)
+				err = dup_anon_vma(prev, curr, &anon_dup);
+		}
+	} else if (merge_prev) {			/* case 2 */
+		if (curr) {
+			vma_start_write(curr);
+			if (end == curr->vm_end) {	/* case 7 */
+				/*
+				 * can_vma_merge_after() assumed we would not be
+				 * removing prev vma, so it skipped the check
+				 * for vm_ops->close, but we are removing curr
+				 */
+				if (curr->vm_ops && curr->vm_ops->close)
+					err = -EINVAL;
+				remove = curr;
+			} else {			/* case 5 */
+				adjust = curr;
+				adj_start = (end - curr->vm_start);
+			}
+			if (!err)
+				err = dup_anon_vma(prev, curr, &anon_dup);
+		}
+	} else { /* merge_next */
+		vma_start_write(next);
+		res = next;
+		if (prev && addr < prev->vm_end) {	/* case 4 */
+			vma_start_write(prev);
+			vma_end = addr;
+			adjust = next;
+			adj_start = -(prev->vm_end - addr);
+			err = dup_anon_vma(next, prev, &anon_dup);
+		} else {
+			/*
+			 * Note that cases 3 and 8 are the ONLY ones where prev
+			 * is permitted to be (but is not necessarily) NULL.
+			 */
+			vma = next;			/* case 3 */
+			vma_start = addr;
+			vma_end = next->vm_end;
+			vma_pgoff = next->vm_pgoff - pglen;
+			if (curr) {			/* case 8 */
+				vma_pgoff = curr->vm_pgoff;
+				vma_start_write(curr);
+				remove = curr;
+				err = dup_anon_vma(next, curr, &anon_dup);
+			}
+		}
+	}
+
+	/* Error in anon_vma clone. */
+	if (err)
+		goto anon_vma_fail;
+
+	if (vma_start < vma->vm_start || vma_end > vma->vm_end)
+		vma_expanded = true;
+
+	if (vma_expanded) {
+		vma_iter_config(vmi, vma_start, vma_end);
+	} else {
+		vma_iter_config(vmi, adjust->vm_start + adj_start,
+				adjust->vm_end);
+	}
+
+	if (vma_iter_prealloc(vmi, vma))
+		goto prealloc_fail;
+
+	init_multi_vma_prep(&vp, vma, adjust, remove, remove2);
+	VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
+		   vp.anon_vma != adjust->anon_vma);
+
+	vma_prepare(&vp);
+	vma_adjust_trans_huge(vma, vma_start, vma_end, adj_start);
+	vma_set_range(vma, vma_start, vma_end, vma_pgoff);
+
+	if (vma_expanded)
+		vma_iter_store(vmi, vma);
+
+	if (adj_start) {
+		adjust->vm_start += adj_start;
+		adjust->vm_pgoff += adj_start >> PAGE_SHIFT;
+		if (adj_start < 0) {
+			WARN_ON(vma_expanded);
+			vma_iter_store(vmi, next);
+		}
+	}
+
+	vma_complete(&vp, vmi, mm);
+	khugepaged_enter_vma(res, vm_flags);
+	return res;
+
+prealloc_fail:
+	if (anon_dup)
+		unlink_anon_vmas(anon_dup);
+
+anon_vma_fail:
+	vma_iter_set(vmi, addr);
+	vma_iter_load(vmi);
+	return NULL;
+}
+
+/*
+ * We are about to modify one or multiple of a VMA's flags, policy, userfaultfd
+ * context and anonymous VMA name within the range [start, end).
+ *
+ * As a result, we might be able to merge the newly modified VMA range with an
+ * adjacent VMA with identical properties.
+ *
+ * If no merge is possible and the range does not span the entirety of the VMA,
+ * we then need to split the VMA to accommodate the change.
+ *
+ * The function returns either the merged VMA, the original VMA if a split was
+ * required instead, or an error if the split failed.
+ */
+struct vm_area_struct *vma_modify(struct vma_iterator *vmi,
+				  struct vm_area_struct *prev,
+				  struct vm_area_struct *vma,
+				  unsigned long start, unsigned long end,
+				  unsigned long vm_flags,
+				  struct mempolicy *policy,
+				  struct vm_userfaultfd_ctx uffd_ctx,
+				  struct anon_vma_name *anon_name)
+{
+	pgoff_t pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
+	struct vm_area_struct *merged;
+
+	merged = vma_merge(vmi, prev, vma, start, end, vm_flags,
+			   pgoff, policy, uffd_ctx, anon_name);
+	if (merged)
+		return merged;
+
+	if (vma->vm_start < start) {
+		int err = split_vma(vmi, vma, start, 1);
+
+		if (err)
+			return ERR_PTR(err);
+	}
+
+	if (vma->vm_end > end) {
+		int err = split_vma(vmi, vma, end, 0);
+
+		if (err)
+			return ERR_PTR(err);
+	}
+
+	return vma;
+}
+
+/*
+ * Attempt to merge a newly mapped VMA with those adjacent to it. The caller
+ * must ensure that [start, end) does not overlap any existing VMA.
+ */
+struct vm_area_struct
+*vma_merge_new_vma(struct vma_iterator *vmi, struct vm_area_struct *prev,
+		   struct vm_area_struct *vma, unsigned long start,
+		   unsigned long end, pgoff_t pgoff)
+{
+	return vma_merge(vmi, prev, vma, start, end, vma->vm_flags, pgoff,
+			 vma_policy(vma), vma->vm_userfaultfd_ctx, anon_vma_name(vma));
+}
+
+/*
+ * Expand vma by delta bytes, potentially merging with an immediately adjacent
+ * VMA with identical properties.
+ */
+struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
+					struct vm_area_struct *vma,
+					unsigned long delta)
+{
+	pgoff_t pgoff = vma->vm_pgoff + vma_pages(vma);
+
+	/* vma is specified as prev, so case 1 or 2 will apply. */
+	return vma_merge(vmi, vma, vma, vma->vm_end, vma->vm_end + delta,
+			 vma->vm_flags, pgoff, vma_policy(vma),
+			 vma->vm_userfaultfd_ctx, anon_vma_name(vma));
+}
+
+void unlink_file_vma_batch_init(struct unlink_vma_file_batch *vb)
+{
+	vb->count = 0;
+}
+
+static void unlink_file_vma_batch_process(struct unlink_vma_file_batch *vb)
+{
+	struct address_space *mapping;
+	int i;
+
+	mapping = vb->vmas[0]->vm_file->f_mapping;
+	i_mmap_lock_write(mapping);
+	for (i = 0; i < vb->count; i++) {
+		VM_WARN_ON_ONCE(vb->vmas[i]->vm_file->f_mapping != mapping);
+		__remove_shared_vm_struct(vb->vmas[i], mapping);
+	}
+	i_mmap_unlock_write(mapping);
+
+	unlink_file_vma_batch_init(vb);
+}
+
+void unlink_file_vma_batch_add(struct unlink_vma_file_batch *vb,
+			       struct vm_area_struct *vma)
+{
+	if (vma->vm_file == NULL)
+		return;
+
+	if ((vb->count > 0 && vb->vmas[0]->vm_file != vma->vm_file) ||
+	    vb->count == ARRAY_SIZE(vb->vmas))
+		unlink_file_vma_batch_process(vb);
+
+	vb->vmas[vb->count] = vma;
+	vb->count++;
+}
+
+void unlink_file_vma_batch_final(struct unlink_vma_file_batch *vb)
+{
+	if (vb->count > 0)
+		unlink_file_vma_batch_process(vb);
+}
+
+/*
+ * Unlink a file-based vm structure from its interval tree, to hide
+ * vma from rmap and vmtruncate before freeing its page tables.
+ */
+void unlink_file_vma(struct vm_area_struct *vma)
+{
+	struct file *file = vma->vm_file;
+
+	if (file) {
+		struct address_space *mapping = file->f_mapping;
+
+		i_mmap_lock_write(mapping);
+		__remove_shared_vm_struct(vma, mapping);
+		i_mmap_unlock_write(mapping);
+	}
+}
+
+void vma_link_file(struct vm_area_struct *vma)
+{
+	struct file *file = vma->vm_file;
+	struct address_space *mapping;
+
+	if (file) {
+		mapping = file->f_mapping;
+		i_mmap_lock_write(mapping);
+		__vma_link_file(vma, mapping);
+		i_mmap_unlock_write(mapping);
+	}
+}
+
+int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
+{
+	VMA_ITERATOR(vmi, mm, 0);
+
+	vma_iter_config(&vmi, vma->vm_start, vma->vm_end);
+	if (vma_iter_prealloc(&vmi, vma))
+		return -ENOMEM;
+
+	vma_start_write(vma);
+	vma_iter_store(&vmi, vma);
+	vma_link_file(vma);
+	mm->map_count++;
+	validate_mm(mm);
+	return 0;
+}
+
+/*
+ * Copy the vma structure to a new location in the same mm,
+ * prior to moving page table entries, to effect an mremap move.
+ */
+struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
+	unsigned long addr, unsigned long len, pgoff_t pgoff,
+	bool *need_rmap_locks)
+{
+	struct vm_area_struct *vma = *vmap;
+	unsigned long vma_start = vma->vm_start;
+	struct mm_struct *mm = vma->vm_mm;
+	struct vm_area_struct *new_vma, *prev;
+	bool faulted_in_anon_vma = true;
+	VMA_ITERATOR(vmi, mm, addr);
+
+	/*
+	 * If anonymous vma has not yet been faulted, update new pgoff
+	 * to match new location, to increase its chance of merging.
+	 */
+	if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) {
+		pgoff = addr >> PAGE_SHIFT;
+		faulted_in_anon_vma = false;
+	}
+
+	new_vma = find_vma_prev(mm, addr, &prev);
+	if (new_vma && new_vma->vm_start < addr + len)
+		return NULL;	/* should never get here */
+
+	new_vma = vma_merge_new_vma(&vmi, prev, vma, addr, addr + len, pgoff);
+	if (new_vma) {
+		/*
+		 * Source vma may have been merged into new_vma
+		 */
+		if (unlikely(vma_start >= new_vma->vm_start &&
+			     vma_start < new_vma->vm_end)) {
+			/*
+			 * The only way we can get a vma_merge with
+			 * self during an mremap is if the vma hasn't
+			 * been faulted in yet and we were allowed to
+			 * reset the dst vma->vm_pgoff to the
+			 * destination address of the mremap to allow
+			 * the merge to happen. mremap must change the
+			 * vm_pgoff linearity between src and dst vmas
+			 * (in turn preventing a vma_merge) to be
+			 * safe. It is only safe to keep the vm_pgoff
+			 * linear if there are no pages mapped yet.
+			 */
+			VM_BUG_ON_VMA(faulted_in_anon_vma, new_vma);
+			*vmap = vma = new_vma;
+		}
+		*need_rmap_locks = (new_vma->vm_pgoff <= vma->vm_pgoff);
+	} else {
+		new_vma = vm_area_dup(vma);
+		if (!new_vma)
+			goto out;
+		vma_set_range(new_vma, addr, addr + len, pgoff);
+		if (vma_dup_policy(vma, new_vma))
+			goto out_free_vma;
+		if (anon_vma_clone(new_vma, vma))
+			goto out_free_mempol;
+		if (new_vma->vm_file)
+			get_file(new_vma->vm_file);
+		if (new_vma->vm_ops && new_vma->vm_ops->open)
+			new_vma->vm_ops->open(new_vma);
+		if (vma_link(mm, new_vma))
+			goto out_vma_link;
+		*need_rmap_locks = false;
+	}
+	return new_vma;
+
+out_vma_link:
+	if (new_vma->vm_ops && new_vma->vm_ops->close)
+		new_vma->vm_ops->close(new_vma);
+
+	if (new_vma->vm_file)
+		fput(new_vma->vm_file);
+
+	unlink_anon_vmas(new_vma);
+out_free_mempol:
+	mpol_put(vma_policy(new_vma));
+out_free_vma:
+	vm_area_free(new_vma);
+out:
+	return NULL;
+}
+
+/*
+ * Rough compatibility check to quickly see if it's even worth looking
+ * at sharing an anon_vma.
+ *
+ * They need to have the same vm_file, and the flags can only differ
+ * in things that mprotect may change.
+ *
+ * NOTE! The fact that we share an anon_vma doesn't _have_ to mean that
+ * we can merge the two vma's. For example, we refuse to merge a vma if
+ * there is a vm_ops->close() function, because that indicates that the
+ * driver is doing some kind of reference counting. But that doesn't
+ * really matter for the anon_vma sharing case.
+ */
+static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *b)
+{
+	return a->vm_end == b->vm_start &&
+		mpol_equal(vma_policy(a), vma_policy(b)) &&
+		a->vm_file == b->vm_file &&
+		!((a->vm_flags ^ b->vm_flags) & ~(VM_ACCESS_FLAGS | VM_SOFTDIRTY)) &&
+		b->vm_pgoff == a->vm_pgoff + ((b->vm_start - a->vm_start) >> PAGE_SHIFT);
+}
+
+/*
+ * Do some basic sanity checking to see if we can re-use the anon_vma
+ * from 'old'. The 'a'/'b' vma's are in VM order - one of them will be
+ * the same as 'old', the other will be the new one that is trying
+ * to share the anon_vma.
+ *
+ * NOTE! This runs with mmap_lock held for reading, so it is possible that
+ * the anon_vma of 'old' is concurrently in the process of being set up
+ * by another page fault trying to merge _that_. But that's ok: if it
+ * is being set up, that automatically means that it will be a singleton
+ * acceptable for merging, so we can do all of this optimistically. But
+ * we do that READ_ONCE() to make sure that we never re-load the pointer.
+ *
+ * IOW: that the "list_is_singular()" test on the anon_vma_chain only
+ * matters for the 'stable anon_vma' case (ie the thing we want to avoid
+ * is to return an anon_vma that is "complex" due to having gone through
+ * a fork).
+ *
+ * We also make sure that the two vma's are compatible (adjacent,
+ * and with the same memory policies). That's all stable, even with just
+ * a read lock on the mmap_lock.
+ */
+static struct anon_vma *reusable_anon_vma(struct vm_area_struct *old,
+					  struct vm_area_struct *a,
+					  struct vm_area_struct *b)
+{
+	if (anon_vma_compatible(a, b)) {
+		struct anon_vma *anon_vma = READ_ONCE(old->anon_vma);
+
+		if (anon_vma && list_is_singular(&old->anon_vma_chain))
+			return anon_vma;
+	}
+	return NULL;
+}
+
+/*
+ * find_mergeable_anon_vma is used by anon_vma_prepare, to check
+ * neighbouring vmas for a suitable anon_vma, before it goes off
+ * to allocate a new anon_vma.  It checks because a repetitive
+ * sequence of mprotects and faults may otherwise lead to distinct
+ * anon_vmas being allocated, preventing vma merge in subsequent
+ * mprotect.
+ */
+struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
+{
+	struct anon_vma *anon_vma = NULL;
+	struct vm_area_struct *prev, *next;
+	VMA_ITERATOR(vmi, vma->vm_mm, vma->vm_end);
+
+	/* Try next first. */
+	next = vma_iter_load(&vmi);
+	if (next) {
+		anon_vma = reusable_anon_vma(next, vma, next);
+		if (anon_vma)
+			return anon_vma;
+	}
+
+	prev = vma_prev(&vmi);
+	VM_BUG_ON_VMA(prev != vma, vma);
+	prev = vma_prev(&vmi);
+	/* Try prev next. */
+	if (prev)
+		anon_vma = reusable_anon_vma(prev, prev, vma);
+
+	/*
+	 * We might reach here with anon_vma == NULL if we can't find
+	 * any reusable anon_vma.
+	 * There's no absolute need to look only at touching neighbours:
+	 * we could search further afield for "compatible" anon_vmas.
+	 * But it would probably just be a waste of time searching,
+	 * or lead to too many vmas hanging off the same anon_vma.
+	 * We're trying to allow mprotect remerging later on,
+	 * not trying to minimize memory used for anon_vmas.
+	 */
+	return anon_vma;
+}
+
+static bool vm_ops_needs_writenotify(const struct vm_operations_struct *vm_ops)
+{
+	return vm_ops && (vm_ops->page_mkwrite || vm_ops->pfn_mkwrite);
+}
+
+static bool vma_is_shared_writable(struct vm_area_struct *vma)
+{
+	return (vma->vm_flags & (VM_WRITE | VM_SHARED)) ==
+		(VM_WRITE | VM_SHARED);
+}
+
+static bool vma_fs_can_writeback(struct vm_area_struct *vma)
+{
+	/* No managed pages to writeback. */
+	if (vma->vm_flags & VM_PFNMAP)
+		return false;
+
+	return vma->vm_file && vma->vm_file->f_mapping &&
+		mapping_can_writeback(vma->vm_file->f_mapping);
+}
+
+/*
+ * Does this VMA require the underlying folios to have their dirty state
+ * tracked?
+ */
+bool vma_needs_dirty_tracking(struct vm_area_struct *vma)
+{
+	/* Only shared, writable VMAs require dirty tracking. */
+	if (!vma_is_shared_writable(vma))
+		return false;
+
+	/* Does the filesystem need to be notified? */
+	if (vm_ops_needs_writenotify(vma->vm_ops))
+		return true;
+
+	/*
+	 * Even if the filesystem doesn't indicate a need for writenotify, if it
+	 * can writeback, dirty tracking is still required.
+	 */
+	return vma_fs_can_writeback(vma);
+}
+
+/*
+ * Some shared mappings will want the pages marked read-only
+ * to track write events. If so, we'll downgrade vm_page_prot
+ * to the private version (using protection_map[] without the
+ * VM_SHARED bit).
+ */
+bool vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot)
+{
+	/* If it was private or non-writable, the write bit is already clear */
+	if (!vma_is_shared_writable(vma))
+		return false;
+
+	/* The backer wishes to know when pages are first written to? */
+	if (vm_ops_needs_writenotify(vma->vm_ops))
+		return true;
+
+	/* The open routine did something to the protections that pgprot_modify
+	 * won't preserve? */
+	if (pgprot_val(vm_page_prot) !=
+	    pgprot_val(vm_pgprot_modify(vm_page_prot, vma->vm_flags)))
+		return false;
+
+	/*
+	 * Do we need to track softdirty? hugetlb does not support softdirty
+	 * tracking yet.
+	 */
+	if (vma_soft_dirty_enabled(vma) && !is_vm_hugetlb_page(vma))
+		return true;
+
+	/* Do we need write faults for uffd-wp tracking? */
+	if (userfaultfd_wp(vma))
+		return true;
+
+	/* Can the mapping track the dirty pages? */
+	return vma_fs_can_writeback(vma);
+}
+
+unsigned long count_vma_pages_range(struct mm_struct *mm,
+				    unsigned long addr, unsigned long end)
+{
+	VMA_ITERATOR(vmi, mm, addr);
+	struct vm_area_struct *vma;
+	unsigned long nr_pages = 0;
+
+	for_each_vma_range(vmi, vma, end) {
+		unsigned long vm_start = max(addr, vma->vm_start);
+		unsigned long vm_end = min(end, vma->vm_end);
+
+		nr_pages += PHYS_PFN(vm_end - vm_start);
+	}
+
+	return nr_pages;
+}
+
+static DEFINE_MUTEX(mm_all_locks_mutex);
+
+static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma)
+{
+	if (!test_bit(0, (unsigned long *) &anon_vma->root->rb_root.rb_root.rb_node)) {
+		/*
+		 * The LSB of head.next can't change from under us
+		 * because we hold the mm_all_locks_mutex.
+		 */
+		down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_lock);
+		/*
+		 * We can safely modify head.next after taking the
+		 * anon_vma->root->rwsem. If some other vma in this mm shares
+		 * the same anon_vma we won't take it again.
+		 *
+		 * No need of atomic instructions here, head.next
+		 * can't change from under us thanks to the
+		 * anon_vma->root->rwsem.
+		 */
+		if (__test_and_set_bit(0, (unsigned long *)
+				       &anon_vma->root->rb_root.rb_root.rb_node))
+			BUG();
+	}
+}
+
+static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)
+{
+	if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
+		/*
+		 * AS_MM_ALL_LOCKS can't change from under us because
+		 * we hold the mm_all_locks_mutex.
+		 *
+		 * Operations on ->flags have to be atomic because
+		 * even if AS_MM_ALL_LOCKS is stable thanks to the
+		 * mm_all_locks_mutex, there may be other cpus
+		 * changing other bitflags in parallel to us.
+		 */
+		if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
+			BUG();
+		down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_lock);
+	}
+}
+
+/*
+ * This operation locks against the VM for all pte/vma/mm related
+ * operations that could ever happen on a certain mm. This includes
+ * vmtruncate, try_to_unmap, and all page faults.
+ *
+ * The caller must take the mmap_lock in write mode before calling
+ * mm_take_all_locks(). The caller isn't allowed to release the
+ * mmap_lock until mm_drop_all_locks() returns.
+ *
+ * mmap_lock in write mode is required in order to block all operations
+ * that could modify pagetables and free pages without need of
+ * altering the vma layout. It's also needed in write mode to avoid new
+ * anon_vmas to be associated with existing vmas.
+ *
+ * A single task can't take more than one mm_take_all_locks() in a row
+ * or it would deadlock.
+ *
+ * The LSB in anon_vma->rb_root.rb_node and the AS_MM_ALL_LOCKS bitflag in
+ * mapping->flags avoid to take the same lock twice, if more than one
+ * vma in this mm is backed by the same anon_vma or address_space.
+ *
+ * We take locks in following order, accordingly to comment at beginning
+ * of mm/rmap.c:
+ *   - all hugetlbfs_i_mmap_rwsem_key locks (aka mapping->i_mmap_rwsem for
+ *     hugetlb mapping);
+ *   - all vmas marked locked
+ *   - all i_mmap_rwsem locks;
+ *   - all anon_vma->rwseml
+ *
+ * We can take all locks within these types randomly because the VM code
+ * doesn't nest them and we protected from parallel mm_take_all_locks() by
+ * mm_all_locks_mutex.
+ *
+ * mm_take_all_locks() and mm_drop_all_locks are expensive operations
+ * that may have to take thousand of locks.
+ *
+ * mm_take_all_locks() can fail if it's interrupted by signals.
+ */
+int mm_take_all_locks(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+	struct anon_vma_chain *avc;
+	VMA_ITERATOR(vmi, mm, 0);
+
+	mmap_assert_write_locked(mm);
+
+	mutex_lock(&mm_all_locks_mutex);
+
+	/*
+	 * vma_start_write() does not have a complement in mm_drop_all_locks()
+	 * because vma_start_write() is always asymmetrical; it marks a VMA as
+	 * being written to until mmap_write_unlock() or mmap_write_downgrade()
+	 * is reached.
+	 */
+	for_each_vma(vmi, vma) {
+		if (signal_pending(current))
+			goto out_unlock;
+		vma_start_write(vma);
+	}
+
+	vma_iter_init(&vmi, mm, 0);
+	for_each_vma(vmi, vma) {
+		if (signal_pending(current))
+			goto out_unlock;
+		if (vma->vm_file && vma->vm_file->f_mapping &&
+				is_vm_hugetlb_page(vma))
+			vm_lock_mapping(mm, vma->vm_file->f_mapping);
+	}
+
+	vma_iter_init(&vmi, mm, 0);
+	for_each_vma(vmi, vma) {
+		if (signal_pending(current))
+			goto out_unlock;
+		if (vma->vm_file && vma->vm_file->f_mapping &&
+				!is_vm_hugetlb_page(vma))
+			vm_lock_mapping(mm, vma->vm_file->f_mapping);
+	}
+
+	vma_iter_init(&vmi, mm, 0);
+	for_each_vma(vmi, vma) {
+		if (signal_pending(current))
+			goto out_unlock;
+		if (vma->anon_vma)
+			list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
+				vm_lock_anon_vma(mm, avc->anon_vma);
+	}
+
+	return 0;
+
+out_unlock:
+	mm_drop_all_locks(mm);
+	return -EINTR;
+}
+
+static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
+{
+	if (test_bit(0, (unsigned long *) &anon_vma->root->rb_root.rb_root.rb_node)) {
+		/*
+		 * The LSB of head.next can't change to 0 from under
+		 * us because we hold the mm_all_locks_mutex.
+		 *
+		 * We must however clear the bitflag before unlocking
+		 * the vma so the users using the anon_vma->rb_root will
+		 * never see our bitflag.
+		 *
+		 * No need of atomic instructions here, head.next
+		 * can't change from under us until we release the
+		 * anon_vma->root->rwsem.
+		 */
+		if (!__test_and_clear_bit(0, (unsigned long *)
+					  &anon_vma->root->rb_root.rb_root.rb_node))
+			BUG();
+		anon_vma_unlock_write(anon_vma);
+	}
+}
+
+static void vm_unlock_mapping(struct address_space *mapping)
+{
+	if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
+		/*
+		 * AS_MM_ALL_LOCKS can't change to 0 from under us
+		 * because we hold the mm_all_locks_mutex.
+		 */
+		i_mmap_unlock_write(mapping);
+		if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
+					&mapping->flags))
+			BUG();
+	}
+}
+
+/*
+ * The mmap_lock cannot be released by the caller until
+ * mm_drop_all_locks() returns.
+ */
+void mm_drop_all_locks(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+	struct anon_vma_chain *avc;
+	VMA_ITERATOR(vmi, mm, 0);
+
+	mmap_assert_write_locked(mm);
+	BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));
+
+	for_each_vma(vmi, vma) {
+		if (vma->anon_vma)
+			list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
+				vm_unlock_anon_vma(avc->anon_vma);
+		if (vma->vm_file && vma->vm_file->f_mapping)
+			vm_unlock_mapping(vma->vm_file->f_mapping);
+	}
+
+	mutex_unlock(&mm_all_locks_mutex);
+}