[PATCH 05/10] mm: abstract vma_merge_new_vma() to use vma_merge_struct

Lorenzo Stoakes
2024-08-05T12:14:41Z

Abstract this function to so we can write tests which use the newly
abstracted interface and maintain a stable interface for tests before/after
refactoring.

We introduce a temporary wrapper vma_merge_new_vma_wrapper() to minimise
the code changes, in a subsequent commit we will entirely refactor this
function.

We also introduce a temporary implementation of vma_merge_modified() for
the same reason - maintaining a common interface to the tests, this will be
removed when vma_merge_modified() is correctly implemented in a subsequent
commit.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
mm/mmap.c | 6 +++---
mm/vma.c | 33 ++++++++++++---------------------
mm/vma.h | 33 ++++++++++++++++++++++++++++++---
tools/testing/vma/vma.c | 12 ++++++++----
4 files changed, 53 insertions(+), 31 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 04145347c245..f6593a81f73d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1494,9 +1494,9 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
* vma again as we may succeed this time.
*/
if (unlikely(vm_flags != vma->vm_flags && prev)) {
- merge = vma_merge_new_vma(&vmi, prev, vma,
- vma->vm_start, vma->vm_end,
- vma->vm_pgoff);
+ merge = vma_merge_new_vma_wrapper(&vmi, prev, vma,
+ vma->vm_start, vma->vm_end,
+ vma->vm_pgoff);
if (merge) {
/*
* ->mmap() can change vma->vm_file and fput
diff --git a/mm/vma.c b/mm/vma.c
index 3d6ce04f1b9c..55615392e8d2 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -1106,6 +1106,11 @@ static struct vm_area_struct *vma_merge(struct vma_merge_struct *vmg)
return NULL;
}

+struct vm_area_struct *vma_merge_modified(struct vma_merge_struct *vmg)
+{
+ return vma_merge(vmg);
+}
+
/*
* We are about to modify one or multiple of a VMA's flags, policy, userfaultfd
* context and anonymous VMA name within the range [start, end).
@@ -1260,27 +1265,14 @@ struct vm_area_struct
* Attempt to merge a newly mapped VMA with those adjacent to it. The caller
* must ensure that [start, end) does not overlap any existing VMA.
*/
-struct vm_area_struct
-*vma_merge_new_vma(struct vma_iterator *vmi, struct vm_area_struct *prev,
- struct vm_area_struct *vma, unsigned long start,
- unsigned long end, pgoff_t pgoff)
+struct vm_area_struct *vma_merge_new_vma(struct vma_merge_struct *vmg)
{
- struct vma_merge_struct vmg = {
- .vmi = vmi,
- .prev = prev,
- .vma = vma,
- .start = start,
- .end = end,
- .flags = vma->vm_flags,
- .file = vma->vm_file,
- .anon_vma = vma->anon_vma,
- .pgoff = pgoff,
- .policy = vma_policy(vma),
- .uffd_ctx = vma->vm_userfaultfd_ctx,
- .anon_name = anon_vma_name(vma),
- };
+ if (!vmg->prev) {
+ vmg->prev = vma_prev(vmg->vmi);
+ vma_iter_set(vmg->vmi, vmg->start);
+ }

- return vma_merge(&vmg);
+ return vma_merge(vmg);
}

/*
@@ -1295,7 +1287,6 @@ struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
struct vma_merge_struct vmg = {
.vmi = vmi,
.prev = vma,
- .vma = vma,
.start = vma->vm_end,
.end = vma->vm_end + delta,
.flags = vma->vm_flags,
@@ -1425,7 +1416,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
if (new_vma && new_vma->vm_start < addr + len)
return NULL; /* should never get here */

- new_vma = vma_merge_new_vma(&vmi, prev, vma, addr, addr + len, pgoff);
+ new_vma = vma_merge_new_vma_wrapper(&vmi, prev, vma, addr, addr + len, pgoff);
if (new_vma) {
/*
* Source vma may have been merged into new_vma
diff --git a/mm/vma.h b/mm/vma.h
index c464d25da120..50459f9e4c7f 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -134,9 +134,36 @@ struct vm_area_struct
struct vm_userfaultfd_ctx new_ctx);

struct vm_area_struct
-*vma_merge_new_vma(struct vma_iterator *vmi, struct vm_area_struct *prev,
- struct vm_area_struct *vma, unsigned long start,
- unsigned long end, pgoff_t pgoff);
+*vma_merge_new_vma(struct vma_merge_struct *vmg);
+
+/* Temporary convenience wrapper. */
+static inline struct vm_area_struct
+*vma_merge_new_vma_wrapper(struct vma_iterator *vmi, struct vm_area_struct *prev,
+ struct vm_area_struct *vma, unsigned long start,
+ unsigned long end, pgoff_t pgoff)
+{
+ struct vma_merge_struct vmg = {
+ .vmi = vmi,
+ .prev = prev,
+ .start = start,
+ .end = end,
+ .flags = vma->vm_flags,
+ .file = vma->vm_file,
+ .anon_vma = vma->anon_vma,
+ .pgoff = pgoff,
+ .policy = vma_policy(vma),
+ .uffd_ctx = vma->vm_userfaultfd_ctx,
+ .anon_name = anon_vma_name(vma),
+ };
+
+ return vma_merge_new_vma(&vmg);
+}
+
+/*
+ * Temporary wrapper around vma_merge() so we can have a common interface for
+ * tests.
+ */
+struct vm_area_struct *vma_merge_modified(struct vma_merge_struct *vmg);

struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
struct vm_area_struct *vma,
diff --git a/tools/testing/vma/vma.c b/tools/testing/vma/vma.c
index d216e51206c1..4416cfa93056 100644
--- a/tools/testing/vma/vma.c
+++ b/tools/testing/vma/vma.c
@@ -53,16 +53,20 @@ static bool test_simple_merge(void)
unsigned long flags = VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE;
struct mm_struct mm = {};
struct vm_area_struct *vma_left = alloc_vma(&mm, 0, 0x1000, 0, flags);
- struct vm_area_struct *vma_middle = alloc_vma(&mm, 0x1000, 0x2000, 1, flags);
struct vm_area_struct *vma_right = alloc_vma(&mm, 0x2000, 0x3000, 2, flags);
VMA_ITERATOR(vmi, &mm, 0x1000);
+ struct vma_merge_struct vmg = {
+ .vmi = &vmi,
+ .start = 0x1000,
+ .end = 0x2000,
+ .flags = flags,
+ .pgoff = 1,
+ };

ASSERT_FALSE(vma_link(&mm, vma_left));
- ASSERT_FALSE(vma_link(&mm, vma_middle));
ASSERT_FALSE(vma_link(&mm, vma_right));

- vma = vma_merge_new_vma(&vmi, vma_left, vma_middle, 0x1000,
- 0x2000, 1);
+ vma = vma_merge_new_vma(&vmg);
ASSERT_NE(vma, NULL);

ASSERT_EQ(vma->vm_start, 0);
--
2.45.2