mmap: convert vma_expand() to use vma iterator

Use the vma iterator instead of the maple state for type safety and for
consistency through the mm code.

Link: https://lkml.kernel.org/r/20230120162650.984577-14-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap.c

@@ -527,7 +527,7 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
  *
  * Returns: 0 on success
  */
-inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
+inline 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)
 {
@@ -556,7 +556,7 @@ inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
 	/* Only handles expanding */
 	VM_BUG_ON(vma->vm_start < start || vma->vm_end > end);
 
-	if (mas_preallocate(mas, GFP_KERNEL))
+	if (vma_iter_prealloc(vmi))
 		goto nomem;
 
 	vma_adjust_trans_huge(vma, start, end, 0);
@@ -581,8 +581,7 @@ inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
 	vma->vm_start = start;
 	vma->vm_end = end;
 	vma->vm_pgoff = pgoff;
-	/* Note: mas must be pointing to the expanding VMA */
-	vma_mas_store(vma, mas);
+	vma_iter_store(vmi, vma);
 
 	if (file) {
 		vma_interval_tree_insert(vma, root);
@@ -2600,7 +2599,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 
 	/* Actually expand, if possible */
 	if (vma &&
-	    !vma_expand(&vmi.mas, vma, merge_start, merge_end, vm_pgoff, next)) {
+	    !vma_expand(&vmi, vma, merge_start, merge_end, vm_pgoff, next)) {
 		khugepaged_enter_vma(vma, vm_flags);
 		goto expanded;
 	}