[PATCH v5 17/21] mm/mmap: Relocate arch_unmap() to vms_complete_munmap_vmas()

["Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>]

From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>

The arch_unmap call was previously moved above the rbtree modifications
in commit 5a28fc94c914 ("x86/mpx, mm/core: Fix recursive munmap()
corruption").  The move was motivated by an issue with calling
arch_unmap() after the rbtree was modified.

Since the above commit, mpx was dropped from the kernel in 45fc24e89b7c
("x86/mpx: remove MPX from arch/x86"), so the motivation for calling
arch_unmap() prior to modifying the vma tree no longer exists
(regardless of rbtree or maple tree implementations).

Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: LEROY Christophe <christophe.leroy2@xxxxxxxxxxxxxxxxxx>
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
---
 mm/mmap.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 9f870e715a47..117e8240f697 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2680,6 +2680,7 @@ static void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
 	mm = vms->mm;
 	mm->map_count -= vms->vma_count;
 	mm->locked_vm -= vms->locked_vm;
+	arch_unmap(mm, vms->start, vms->end); /* write lock needed */
 	if (vms->unlock)
 		mmap_write_downgrade(mm);
 
@@ -2907,7 +2908,7 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
  *
  * This function takes a @mas that is either pointing to the previous VMA or set
  * to MA_START and sets it up to remove the mapping(s).  The @len will be
- * aligned and any arch_unmap work will be preformed.
+ * aligned prior to munmap.
  *
  * Return: 0 on success and drops the lock if so directed, error and leaves the
  * lock held otherwise.
@@ -2927,16 +2928,12 @@ int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
 		return -EINVAL;
 
 	/*
-	 * Check if memory is sealed before arch_unmap.
 	 * Prevent unmapping a sealed VMA.
 	 * can_modify_mm assumes we have acquired the lock on MM.
 	 */
 	if (unlikely(!can_modify_mm(mm, start, end)))
 		return -EPERM;
 
-	 /* arch_unmap() might do unmaps itself.  */
-	arch_unmap(mm, start, end);
-
 	/* Find the first overlapping VMA */
 	vma = vma_find(vmi, end);
 	if (!vma) {
@@ -2997,9 +2994,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	if (unlikely(!can_modify_mm(mm, addr, end)))
 		return -EPERM;
 
-	 /* arch_unmap() might do unmaps itself.  */
-	arch_unmap(mm, addr, end);
-
 	/* Find the first overlapping VMA */
 	vma = vma_find(&vmi, end);
 	init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
@@ -3377,14 +3371,12 @@ int do_vma_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	struct mm_struct *mm = vma->vm_mm;
 
 	/*
-	 * Check if memory is sealed before arch_unmap.
 	 * Prevent unmapping a sealed VMA.
 	 * can_modify_mm assumes we have acquired the lock on MM.
 	 */
 	if (unlikely(!can_modify_mm(mm, start, end)))
 		return -EPERM;
 
-	arch_unmap(mm, start, end);
 	return do_vmi_align_munmap(vmi, vma, mm, start, end, uf, unlock);
 }
 
-- 
2.43.0