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

Mike Rapoport
2025-08-14T08:44:07Z

On Tue, Aug 12, 2025 at 04:44:19PM +0100, Lorenzo Stoakes wrote:
> 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>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
> 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
>

--
Sincerely yours,
Mike.