From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: nommu: remove uses of VMA linked list

Use the maple tree or VMA iterator instead.  This is faster and will allow
us to shrink the VMA.

Link: https://lkml.kernel.org/r/20220426150616.3937571-67-Liam.Howlett@oracle.com
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/nommu.c |   15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

--- a/mm/nommu.c~nommu-remove-uses-of-vma-linked-list
+++ a/mm/nommu.c
@@ -1383,6 +1383,7 @@ static int shrink_vma(struct mm_struct *
  */
 int do_munmap(struct mm_struct *mm, unsigned long start, size_t len, struct list_head *uf)
 {
+	MA_STATE(mas, &mm->mm_mt, start, start);
 	struct vm_area_struct *vma;
 	unsigned long end;
 	int ret;
@@ -1394,7 +1395,7 @@ int do_munmap(struct mm_struct *mm, unsi
 	end = start + len;
 
 	/* find the first potentially overlapping VMA */
-	vma = find_vma(mm, start);
+	vma = mas_find(&mas, end - 1);
 	if (!vma) {
 		static int limit;
 		if (limit < 5) {
@@ -1413,7 +1414,7 @@ int do_munmap(struct mm_struct *mm, unsi
 				return -EINVAL;
 			if (end == vma->vm_end)
 				goto erase_whole_vma;
-			vma = vma->vm_next;
+			vma = mas_next(&mas, end - 1);
 		} while (vma);
 		return -EINVAL;
 	} else {
@@ -1462,6 +1463,7 @@ SYSCALL_DEFINE2(munmap, unsigned long, a
  */
 void exit_mmap(struct mm_struct *mm)
 {
+	VMA_ITERATOR(vmi, mm, 0);
 	struct vm_area_struct *vma;
 
 	if (!mm)
@@ -1469,12 +1471,17 @@ void exit_mmap(struct mm_struct *mm)
 
 	mm->total_vm = 0;
 
-	while ((vma = mm->mmap)) {
-		mm->mmap = vma->vm_next;
+	/*
+	 * Lock the mm to avoid assert complaining even though this is the only
+	 * user of the mm
+	 */
+	mmap_write_lock(mm);
+	for_each_vma(vmi, vma) {
 		delete_vma_from_mm(vma);
 		delete_vma(mm, vma);
 		cond_resched();
 	}
+	mmap_write_unlock(mm);
 	__mt_destroy(&mm->mm_mt);
 }
 
_