mm/vma: introduce vmi_complete_munmap_vmas()

Extract all necessary operations that need to be completed after the vma
maple tree is updated from a munmap() operation.  Extracting this makes
the later patch in the series easier to understand.

Link: https://lkml.kernel.org/r/20240830040101.822209-4-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Bert Karwatzki <spasswolf@web.de>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: Jiri Olsa <olsajiri@gmail.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vma.c

@@ -684,6 +684,58 @@ static inline void abort_munmap_vmas(struct ma_state *mas_detach)
 	__mt_destroy(mas_detach->tree);
 }
 
+/*
+ * vmi_complete_munmap_vmas() - Finish the munmap() operation
+ * @vmi: The vma iterator
+ * @vma: The first vma to be munmapped
+ * @mm: The mm struct
+ * @start: The start address
+ * @end: The end address
+ * @unlock: Unlock the mm or not
+ * @mas_detach: them maple state of the detached vma maple tree
+ * @locked_vm: The locked_vm count in the detached vmas
+ *
+ * This function updates the mm_struct, unmaps the region, frees the resources
+ * used for the munmap() and may downgrade the lock - if requested.  Everything
+ * needed to be done once the vma maple tree is updated.
+ */
+static void
+vmi_complete_munmap_vmas(struct vma_iterator *vmi, struct vm_area_struct *vma,
+		struct mm_struct *mm, unsigned long start, unsigned long end,
+		bool unlock, struct ma_state *mas_detach,
+		unsigned long locked_vm)
+{
+	struct vm_area_struct *prev, *next;
+	int count;
+
+	count = mas_detach->index + 1;
+	mm->map_count -= count;
+	mm->locked_vm -= locked_vm;
+	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(mas_detach->tree);
+}
+
 /*
  * do_vmi_align_munmap() - munmap the aligned region from @start to @end.
  * @vmi: The vma iterator
@@ -703,7 +755,7 @@ 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 vm_area_struct *next = NULL;
 	struct maple_tree mt_detach;
 	int count = 0;
 	int error = -ENOMEM;
@@ -818,31 +870,9 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		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);
+	vmi_complete_munmap_vmas(vmi, vma, mm, start, end, unlock, &mas_detach,
+				 locked_vm);
 
-	__mt_destroy(&mt_detach);
 	return 0;
 
 modify_vma_failed: