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

[Mike Rapoport]

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@xxxxxxxxxx>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>

> ---
>  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.