mm/mmap: use the maple tree in find_vma() instead of the rbtree.

Using the maple tree interface mt_find() will handle the RCU locking and
will start searching at the address up to the limit, ULONG_MAX in this
case.

Add kernel documentation to this API.

Link: https://lkml.kernel.org/r/20220906194824.2110408-12-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: David Hildenbrand <david@redhat.com>
Tested-by: Yu Zhao <yuzhao@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap.c

@@ -2449,11 +2449,18 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
 
 EXPORT_SYMBOL(get_unmapped_area);
 
-/* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
+/**
+ * find_vma() - Find the VMA for a given address, or the next VMA.
+ * @mm: The mm_struct to check
+ * @addr: The address
+ *
+ * Returns: The VMA associated with addr, or the next VMA.
+ * May return %NULL in the case of no VMA at addr or above.
+ */
 struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
 {
-	struct rb_node *rb_node;
 	struct vm_area_struct *vma;
+	unsigned long index = addr;
 
 	mmap_assert_locked(mm);
 	/* Check the cache first. */
@@ -2461,22 +2468,7 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
 	if (likely(vma))
 		return vma;
 
-	rb_node = mm->mm_rb.rb_node;
-
-	while (rb_node) {
-		struct vm_area_struct *tmp;
-
-		tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);
-
-		if (tmp->vm_end > addr) {
-			vma = tmp;
-			if (tmp->vm_start <= addr)
-				break;
-			rb_node = rb_node->rb_left;
-		} else
-			rb_node = rb_node->rb_right;
-	}
-
+	vma = mt_find(&mm->mm_mt, &index, ULONG_MAX);
 	if (vma)
 		vmacache_update(addr, vma);
 	return vma;