[PATCH v3 44/48] mm/mmap: Don't use __vma_adjust() in shift_arg_pages()

Liam Howlett
2023-01-17T02:40:03Z

Introduce shrink_vma() which uses the vma_prepare() and vma_complete()
functions to reduce the vma coverage.

Convert shift_arg_pages() to use expand_vma() and the new shrink_vma()
function. Remove support from __vma_adjust() to reduce a vma size since
shift_arg_pages() is the only user that shrinks a VMA in this way.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
fs/exec.c | 4 ++--
include/linux/mm.h | 13 ++++------
mm/mmap.c | 59 ++++++++++++++++++++++++++++++++++++----------
3 files changed, 53 insertions(+), 23 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index d52fca2dd30b..c0df813d2b45 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -699,7 +699,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
/*
* cover the whole range: [new_start, old_end)
*/
- if (vma_adjust(&vmi, vma, new_start, old_end, vma->vm_pgoff))
+ if (vma_expand(&vmi, vma, new_start, old_end, vma->vm_pgoff, NULL))
return -ENOMEM;

/*
@@ -733,7 +733,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)

vma_prev(&vmi);
/* Shrink the vma to just the new range */
- return vma_adjust(&vmi, vma, new_start, new_end, vma->vm_pgoff);
+ return vma_shrink(&vmi, vma, new_start, new_end, vma->vm_pgoff);
}

/*
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a00871cc63cc..0b229ddf43a4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2822,14 +2822,11 @@ void anon_vma_interval_tree_verify(struct anon_vma_chain *node);

/* mmap.c */
extern int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin);
-extern int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma, unsigned long start,
- unsigned long end, pgoff_t pgoff, struct vm_area_struct *expand);
-static inline int vma_adjust(struct vma_iterator *vmi,
- struct vm_area_struct *vma, unsigned long start, unsigned long end,
- pgoff_t pgoff)
-{
- return __vma_adjust(vmi, vma, start, end, pgoff, NULL);
-}
+extern int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
+ unsigned long start, unsigned long end, pgoff_t pgoff,
+ struct vm_area_struct *next);
+extern int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
+ unsigned long start, unsigned long end, pgoff_t pgoff);
extern struct vm_area_struct *vma_merge(struct vma_iterator *vmi,
struct mm_struct *, struct vm_area_struct *prev, unsigned long addr,
unsigned long end, unsigned long vm_flags, struct anon_vma *,
diff --git a/mm/mmap.c b/mm/mmap.c
index a8c941e3be84..a6e07edc15e9 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -637,10 +637,9 @@ static inline void vma_complete(struct vma_prepare *vp,
*
* Returns: 0 on success
*/
-inline int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
- unsigned long start, unsigned long end, pgoff_t pgoff,
- struct vm_area_struct *next)
-
+int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
+ unsigned long start, unsigned long end, pgoff_t pgoff,
+ struct vm_area_struct *next)
{
bool remove_next = false;
struct vma_prepare vp;
@@ -686,6 +685,44 @@ inline int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
nomem:
return -ENOMEM;
}
+
+/*
+ * vma_shrink() - Reduce an existing VMAs memory area
+ * @vmi: The vma iterator
+ * @vma: The VMA to modify
+ * @start: The new start
+ * @end: The new end
+ *
+ * Returns: 0 on success, -ENOMEM otherwise
+ */
+int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
+ unsigned long start, unsigned long end, pgoff_t pgoff)
+{
+ struct vma_prepare vp;
+
+ WARN_ON((vma->vm_start != start) && (vma->vm_end != end));
+
+ if (vma_iter_prealloc(vmi, vma))
+ return -ENOMEM;
+
+ init_vma_prep(&vp, vma);
+ vma_adjust_trans_huge(vma, start, end, 0);
+ vma_prepare(&vp);
+
+ if (vma->vm_start < start)
+ vma_iter_clear(vmi, vma->vm_start, start);
+
+ if (vma->vm_end > end)
+ vma_iter_clear(vmi, end, vma->vm_end);
+
+ vma->vm_start = start;
+ vma->vm_end = end;
+ vma->vm_pgoff = pgoff;
+ vma_complete(&vp, vmi, vma->vm_mm);
+ validate_mm(vma->vm_mm);
+ return 0;
+}
+
/*
* We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
* is already present in an i_mmap tree without adjusting the tree.
@@ -801,14 +838,7 @@ int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,

vma_prepare(&vma_prep);

- if (vma->vm_start < start)
- vma_iter_clear(vmi, vma->vm_start, start);
- else if (start != vma->vm_start)
- vma_changed = true;
-
- if (vma->vm_end > end)
- vma_iter_clear(vmi, end, vma->vm_end);
- else if (end != vma->vm_end)
+ if (start < vma->vm_start || end > vma->vm_end)
vma_changed = true;

vma->vm_start = start;
@@ -821,7 +851,10 @@ int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,
if (adjust_next) {
next->vm_start += adjust_next;
next->vm_pgoff += adjust_next >> PAGE_SHIFT;
- vma_iter_store(vmi, next);
+ if (adjust_next < 0) {
+ WARN_ON_ONCE(vma_changed);
+ vma_iter_store(vmi, next);
+ }
}

vma_complete(&vma_prep, vmi, mm);
--
2.35.1