From: Lorenzo Stoakes Date: Tue, 12 Aug 2025 15:44:17 +0000 (+0100) Subject: mm: update fork mm->flags initialisation to use bitmap X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=19148a19da86f1b7d1a1b067c9f656b0f3a60fb1;p=users%2Fhch%2Fmisc.git mm: update fork mm->flags initialisation to use bitmap We now need to account for flag initialisation on fork. We retain the existing logic as much as we can, but dub the existing flag mask legacy. These flags are therefore required to fit in the first 32-bits of the flags field. However, further flag propagation upon fork can be implemented in mm_init() on a per-flag basis. We ensure we clear the entire bitmap prior to setting it, and use __mm_flags_get_word() and __mm_flags_set_word() to manipulate these legacy fields efficiently. Link: https://lkml.kernel.org/r/9fb8954a7a0f0184f012a8e66f8565bcbab014ba.1755012943.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes Reviewed-by: Liam R. Howlett Reviewed-by: Mike Rapoport (Microsoft) Acked-by: David Hildenbrand Cc: Adrian Hunter Cc: Alexander Gordeev Cc: Alexander Shishkin Cc: Al Viro Cc: Andreas Larsson Cc: Andy Lutomirski Cc: Arnaldo Carvalho de Melo Cc: Baolin Wang Cc: Barry Song Cc: Ben Segall Cc: Borislav Betkov Cc: Chengming Zhou Cc: Christian Borntraeger Cc: Christian Brauner Cc: David Rientjes Cc: David S. Miller Cc: Dev Jain Cc: Dietmar Eggemann Cc: Gerald Schaefer Cc: Heiko Carstens Cc: "H. Peter Anvin" Cc: Ian Rogers Cc: Ingo Molnar Cc: Jan Kara Cc: Jann Horn Cc: Jason Gunthorpe Cc: Jiri Olsa Cc: John Hubbard Cc: Juri Lelli Cc: Kan Liang Cc: Kees Cook Cc: Marc Rutland Cc: Mariano Pache Cc: "Masami Hiramatsu (Google)" Cc: Mateusz Guzik Cc: Matthew Wilcox (Oracle) Cc: Mel Gorman Cc: Michal Hocko Cc: Namhyung kim Cc: Oleg Nesterov Cc: Peter Xu Cc: Peter Zijlstra Cc: Ryan Roberts Cc: Shakeel Butt Cc: Steven Rostedt Cc: Suren Baghdasaryan Cc: Sven Schnelle Cc: Thomas Gleinxer Cc: Valentin Schneider Cc: Vasily Gorbik Cc: Vincent Guittot Cc: Vlastimil Babka Cc: xu xin Cc: Zi Yan Signed-off-by: Andrew Morton --- diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index de09ae2a0de6..69ce407b4343 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1831,16 +1831,23 @@ enum { #define MMF_TOPDOWN 31 /* mm searches top down by default */ #define MMF_TOPDOWN_MASK BIT(MMF_TOPDOWN) -#define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ +#define MMF_INIT_LEGACY_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ MMF_DISABLE_THP_MASK | MMF_HAS_MDWE_MASK |\ MMF_VM_MERGE_ANY_MASK | MMF_TOPDOWN_MASK) -static inline unsigned long mmf_init_flags(unsigned long flags) +/* Legacy flags must fit within 32 bits. */ +static_assert((u64)MMF_INIT_LEGACY_MASK <= (u64)UINT_MAX); + +/* + * Initialise legacy flags according to masks, propagating selected flags on + * fork. Further flag manipulation can be performed by the caller. + */ +static inline unsigned long mmf_init_legacy_flags(unsigned long flags) { if (flags & (1UL << MMF_HAS_MDWE_NO_INHERIT)) flags &= ~((1UL << MMF_HAS_MDWE) | (1UL << MMF_HAS_MDWE_NO_INHERIT)); - return flags & MMF_INIT_MASK; + return flags & MMF_INIT_LEGACY_MASK; } #endif /* _LINUX_MM_TYPES_H */ diff --git a/kernel/fork.c b/kernel/fork.c index af673856499d..b04ecba4a709 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1057,11 +1057,14 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, mm_init_uprobes_state(mm); hugetlb_count_init(mm); + mm_flags_clear_all(mm); if (current->mm) { - mm->flags = mmf_init_flags(current->mm->flags); + unsigned long flags = __mm_flags_get_word(current->mm); + + __mm_flags_set_word(mm, mmf_init_legacy_flags(flags)); mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK; } else { - mm->flags = default_dump_filter; + __mm_flags_set_word(mm, default_dump_filter); mm->def_flags = 0; }