[PATCH 10/10] mm: replace mm->flags with bitmap entirely and set to 64 bits

Lorenzo Stoakes
2025-08-12T15:48:46Z

Now we have updated all users of mm->flags to use the bitmap accessors,
repalce it with the bitmap version entirely.

We are then able to move to having 64 bits of mm->flags on both 32-bit and
64-bit architectures.

We also update the VMA userland tests to ensure that everything remains
functional there.

No functional changes intended, other than there now being 64 bits of
available mm_struct flags.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
include/linux/mm.h | 12 ++++++------
include/linux/mm_types.h | 14 +++++---------
include/linux/sched/coredump.h | 2 +-
tools/testing/vma/vma_internal.h | 19 +++++++++++++++++--
4 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 34311ebe62cc..b61e2d4858cf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -724,32 +724,32 @@ static inline void assert_fault_locked(struct vm_fault *vmf)

static inline bool mm_flags_test(int flag, const struct mm_struct *mm)
{
- return test_bit(flag, ACCESS_PRIVATE(&mm->_flags, __mm_flags));
+ return test_bit(flag, ACCESS_PRIVATE(&mm->flags, __mm_flags));
}

static inline bool mm_flags_test_and_set(int flag, struct mm_struct *mm)
{
- return test_and_set_bit(flag, ACCESS_PRIVATE(&mm->_flags, __mm_flags));
+ return test_and_set_bit(flag, ACCESS_PRIVATE(&mm->flags, __mm_flags));
}

static inline bool mm_flags_test_and_clear(int flag, struct mm_struct *mm)
{
- return test_and_clear_bit(flag, ACCESS_PRIVATE(&mm->_flags, __mm_flags));
+ return test_and_clear_bit(flag, ACCESS_PRIVATE(&mm->flags, __mm_flags));
}

static inline void mm_flags_set(int flag, struct mm_struct *mm)
{
- set_bit(flag, ACCESS_PRIVATE(&mm->_flags, __mm_flags));
+ set_bit(flag, ACCESS_PRIVATE(&mm->flags, __mm_flags));
}

static inline void mm_flags_clear(int flag, struct mm_struct *mm)
{
- clear_bit(flag, ACCESS_PRIVATE(&mm->_flags, __mm_flags));
+ clear_bit(flag, ACCESS_PRIVATE(&mm->flags, __mm_flags));
}

static inline void mm_flags_clear_all(struct mm_struct *mm)
{
- bitmap_zero(ACCESS_PRIVATE(&mm->_flags, __mm_flags), NUM_MM_FLAG_BITS);
+ bitmap_zero(ACCESS_PRIVATE(&mm->flags, __mm_flags), NUM_MM_FLAG_BITS);
}

extern const struct vm_operations_struct vma_dummy_vm_ops;
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 25577ab39094..47d2e4598acd 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -932,7 +932,7 @@ struct mm_cid {
* Opaque type representing current mm_struct flag state. Must be accessed via
* mm_flags_xxx() helper functions.
*/
-#define NUM_MM_FLAG_BITS BITS_PER_LONG
+#define NUM_MM_FLAG_BITS (64)
typedef struct {
__private DECLARE_BITMAP(__mm_flags, NUM_MM_FLAG_BITS);
} mm_flags_t;
@@ -1119,11 +1119,7 @@ struct mm_struct {
/* Architecture-specific MM context */
mm_context_t context;

- /* Temporary union while we convert users to mm_flags_t. */
- union {
- unsigned long flags; /* Must use atomic bitops to access */
- mm_flags_t _flags; /* Must use mm_flags_* helpers to access */
- };
+ mm_flags_t flags; /* Must use mm_flags_* hlpers to access */

#ifdef CONFIG_AIO
spinlock_t ioctx_lock;
@@ -1236,7 +1232,7 @@ struct mm_struct {
/* Read the first system word of mm flags, non-atomically. */
static inline unsigned long __mm_flags_get_word(struct mm_struct *mm)
{
- unsigned long *bitmap = ACCESS_PRIVATE(&mm->_flags, __mm_flags);
+ unsigned long *bitmap = ACCESS_PRIVATE(&mm->flags, __mm_flags);

return bitmap_read(bitmap, 0, BITS_PER_LONG);
}
@@ -1245,7 +1241,7 @@ static inline unsigned long __mm_flags_get_word(struct mm_struct *mm)
static inline void __mm_flags_set_word(struct mm_struct *mm,
unsigned long value)
{
- unsigned long *bitmap = ACCESS_PRIVATE(&mm->_flags, __mm_flags);
+ unsigned long *bitmap = ACCESS_PRIVATE(&mm->flags, __mm_flags);

bitmap_copy(bitmap, &value, BITS_PER_LONG);
}
@@ -1253,7 +1249,7 @@ static inline void __mm_flags_set_word(struct mm_struct *mm,
/* Obtain a read-only view of the bitmap. */
static inline const unsigned long *__mm_flags_get_bitmap(const struct mm_struct *mm)
{
- return (const unsigned long *)ACCESS_PRIVATE(&mm->_flags, __mm_flags);
+ return (const unsigned long *)ACCESS_PRIVATE(&mm->flags, __mm_flags);
}

#define MM_MT_FLAGS (MT_FLAGS_ALLOC_RANGE | MT_FLAGS_LOCK_EXTERN | \
diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h
index 19ecfcceb27a..079ae5a97480 100644
--- a/include/linux/sched/coredump.h
+++ b/include/linux/sched/coredump.h
@@ -20,7 +20,7 @@ static inline unsigned long __mm_flags_get_dumpable(struct mm_struct *mm)

static inline void __mm_flags_set_mask_dumpable(struct mm_struct *mm, int value)
{
- unsigned long *bitmap = ACCESS_PRIVATE(&mm->_flags, __mm_flags);
+ unsigned long *bitmap = ACCESS_PRIVATE(&mm->flags, __mm_flags);

set_mask_bits(bitmap, MMF_DUMPABLE_MASK, value);
}
diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
index cb1c2a8afe26..f13354bf0a1e 100644
--- a/tools/testing/vma/vma_internal.h
+++ b/tools/testing/vma/vma_internal.h
@@ -249,6 +249,14 @@ struct mutex {};
#define DEFINE_MUTEX(mutexname) \
struct mutex mutexname = {}

+#define DECLARE_BITMAP(name, bits) \
+ unsigned long name[BITS_TO_LONGS(bits)]
+
+#define NUM_MM_FLAG_BITS (64)
+typedef struct {
+ __private DECLARE_BITMAP(__mm_flags, NUM_MM_FLAG_BITS);
+} mm_flags_t;
+
struct mm_struct {
struct maple_tree mm_mt;
int map_count; /* number of VMAs */
@@ -260,7 +268,7 @@ struct mm_struct {

unsigned long def_flags;

- unsigned long flags; /* Must use atomic bitops to access */
+ mm_flags_t flags; /* Must use mm_flags_* helpers to access */
};

struct vm_area_struct;
@@ -1333,6 +1341,13 @@ static inline void userfaultfd_unmap_complete(struct mm_struct *mm,
{
}

+# define ACCESS_PRIVATE(p, member) ((p)->member)
+
+static inline bool mm_flags_test(int flag, const struct mm_struct *mm)
+{
+ return test_bit(flag, ACCESS_PRIVATE(&mm->flags, __mm_flags));
+}
+
/*
* Denies creating a writable executable mapping or gaining executable permissions.
*
@@ -1363,7 +1378,7 @@ static inline void userfaultfd_unmap_complete(struct mm_struct *mm,
static inline bool map_deny_write_exec(unsigned long old, unsigned long new)
{
/* If MDWE is disabled, we have nothing to deny. */
- if (!test_bit(MMF_HAS_MDWE, &current->mm->flags))
+ if (mm_flags_test(MMF_HAS_MDWE, current->mm))
return false;

/* If the new VMA is not executable, we have nothing to deny. */
--
2.50.1