mm: add VMA iterator

This thin layer of abstraction over the maple tree state is for iterating
over VMAs.  You can go forwards, go backwards or ask where the iterator
is.  Rename the existing vma_next() to __vma_next() -- it will be removed
by the end of this series.

Link: https://lkml.kernel.org/r/20220906194824.2110408-10-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>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Tested-by: Yu Zhao <yuzhao@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Howells <dhowells@redhat.com>
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>

Author: Matthew Wilcox (Oracle)

include/linux/mm.h

@@ -661,6 +661,38 @@ static inline bool vma_is_accessible(struct vm_area_struct *vma)
 	return vma->vm_flags & VM_ACCESS_FLAGS;
 }
 
+static inline
+struct vm_area_struct *vma_find(struct vma_iterator *vmi, unsigned long max)
+{
+	return mas_find(&vmi->mas, max);
+}
+
+static inline struct vm_area_struct *vma_next(struct vma_iterator *vmi)
+{
+	/*
+	 * Uses vma_find() to get the first VMA when the iterator starts.
+	 * Calling mas_next() could skip the first entry.
+	 */
+	return vma_find(vmi, ULONG_MAX);
+}
+
+static inline struct vm_area_struct *vma_prev(struct vma_iterator *vmi)
+{
+	return mas_prev(&vmi->mas, 0);
+}
+
+static inline unsigned long vma_iter_addr(struct vma_iterator *vmi)
+{
+	return vmi->mas.index;
+}
+
+#define for_each_vma(__vmi, __vma)					\
+	while (((__vma) = vma_next(&(__vmi))) != NULL)
+
+/* The MM code likes to work with exclusive end addresses */
+#define for_each_vma_range(__vmi, __vma, __end)				\
+	while (((__vma) = vma_find(&(__vmi), (__end) - 1)) != NULL)
+
 #ifdef CONFIG_SHMEM
 /*
  * The vma_is_shmem is not inline because it is used only by slow

include/linux/mm_types.h

@@ -777,6 +777,27 @@ static inline void lru_gen_use_mm(struct mm_struct *mm)
 
 #endif /* CONFIG_LRU_GEN */
 
+struct vma_iterator {
+	struct ma_state mas;
+};
+
+#define VMA_ITERATOR(name, __mm, __addr)				\
+	struct vma_iterator name = {					\
+		.mas = {						\
+			.tree = &(__mm)->mm_mt,				\
+			.index = __addr,				\
+			.node = MAS_START,				\
+		},							\
+	}
+
+static inline void vma_iter_init(struct vma_iterator *vmi,
+		struct mm_struct *mm, unsigned long addr)
+{
+	vmi->mas.tree = &mm->mm_mt;
+	vmi->mas.index = addr;
+	vmi->mas.node = MAS_START;
+}
+
 struct mmu_gather;
 extern void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm);
 extern void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm);

mm/mmap.c

@@ -586,15 +586,15 @@ static int find_vma_links(struct mm_struct *mm, unsigned long addr,
 }
 
 /*
- * vma_next() - Get the next VMA.
+ * __vma_next() - Get the next VMA.
  * @mm: The mm_struct.
  * @vma: The current vma.
  *
  * If @vma is NULL, return the first vma in the mm.
  *
  * Returns: The next VMA after @vma.
  */
-static inline struct vm_area_struct *vma_next(struct mm_struct *mm,
+static inline struct vm_area_struct *__vma_next(struct mm_struct *mm,
 					 struct vm_area_struct *vma)
 {
 	if (!vma)
@@ -1291,7 +1291,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
 	if (vm_flags & VM_SPECIAL)
 		return NULL;
 
-	next = vma_next(mm, prev);
+	next = __vma_next(mm, prev);
 	area = next;
 	if (area && area->vm_end == end)		/* cases 6, 7, 8 */
 		next = next->vm_next;
@@ -2843,7 +2843,7 @@ static void unmap_region(struct mm_struct *mm,
 		struct vm_area_struct *vma, struct vm_area_struct *prev,
 		unsigned long start, unsigned long end)
 {
-	struct vm_area_struct *next = vma_next(mm, prev);
+	struct vm_area_struct *next = __vma_next(mm, prev);
 	struct mmu_gather tlb;
 
 	lru_add_drain();
@@ -3051,7 +3051,7 @@ int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
 		if (error)
 			goto split_failed;
 	}
-	vma = vma_next(mm, prev);
+	vma = __vma_next(mm, prev);
 
 	if (unlikely(uf)) {
 		/*