mm code often needs to know whether some mm represents a kernel or user address space. This is currently done by comparing the mm pointer with &init_mm; besides not being particularly elegant, this ignores the fact that other mm's (e.g. efi_mm) may also represent parts of the kernel address space.
Introduce a new mm flag MMF_KERNEL and set it for init_mm. Subsequent patches will use this flag to replace comparisons with &init_mm. No functional change is introduced for now. Assisted-by: Codex:GPT-5.5 Signed-off-by: Kevin Brodsky <[email protected]> --- include/linux/mm_types.h | 10 ++++++++++ mm/init-mm.c | 1 + 2 files changed, 11 insertions(+) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index a2e0dc5892ff..7838ea3aac00 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1414,6 +1414,8 @@ struct mm_struct { char flexible_array[] __aligned(__alignof__(unsigned long)); }; +#define MM_FLAGS_INIT(flags) { .__mm_flags = { BITMAP_FROM_U64(flags) } } + static inline bool mm_flags_test(int flag, const struct mm_struct *mm) { return test_bit(flag, ACCESS_PRIVATE(&mm->flags, __mm_flags)); @@ -2001,6 +2003,9 @@ enum { #define MMF_TOPDOWN 31 /* mm searches top down by default */ #define MMF_TOPDOWN_MASK BIT(MMF_TOPDOWN) +#define MMF_KERNEL 32 /* mm belongs to the kernel */ +#define MMF_KERNEL_MASK BIT_ULL(MMF_KERNEL) + #define MMF_INIT_LEGACY_MASK (MMF_DUMP_FILTER_MASK |\ MMF_DISABLE_THP_MASK | MMF_HAS_MDWE_MASK |\ MMF_VM_MERGE_ANY_MASK | MMF_TOPDOWN_MASK) @@ -2008,6 +2013,11 @@ enum { /* Legacy flags must fit within 32 bits. */ static_assert((u64)MMF_INIT_LEGACY_MASK <= (u64)UINT_MAX); +static inline bool mm_is_kernel(const struct mm_struct *mm) +{ + return mm && mm_flags_test(MMF_KERNEL, mm); +} + /* * Initialise legacy flags according to masks, propagating selected flags on * fork. Further flag manipulation can be performed by the caller. diff --git a/mm/init-mm.c b/mm/init-mm.c index 3e792aad7626..93773269bf87 100644 --- a/mm/init-mm.c +++ b/mm/init-mm.c @@ -34,6 +34,7 @@ struct mm_struct init_mm = { .pgd = swapper_pg_dir, .mm_users = ATOMIC_INIT(2), .mm_count = ATOMIC_INIT(1), + .flags = MM_FLAGS_INIT(MMF_KERNEL_MASK), .write_protect_seq = SEQCNT_ZERO(init_mm.write_protect_seq), MMAP_LOCK_INITIALIZER(init_mm) .page_table_lock = __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock), -- 2.51.2
