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scancount=1 engine=8.12.0-2508110000 definitions=main-2508260125 X-Proofpoint-GUID: lav0GmRnfN_7C6Wa7vu30twD7JewO7PM X-Proofpoint-ORIG-GUID: lav0GmRnfN_7C6Wa7vu30twD7JewO7PM X-Authority-Analysis: v=2.4 cv=NrLRc9dJ c=1 sm=1 tr=0 ts=68adc2f2 b=1 cx=c_pps a=WeWmnZmh0fydH62SvGsd2A==:117 a=WeWmnZmh0fydH62SvGsd2A==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=kj9zAlcOel0A:10 a=2OwXVqhp2XgA:10 a=GoEa3M9JfhUA:10 a=yPCof4ZbAAAA:8 a=20KFwNOVAAAA:8 a=uteFWKwLDzXGDGXyEYEA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwODIzMDAzNSBTYWx0ZWRfXznfofIsaJF0x 0BJSSH3ysH/w3XrvRlI17+/HCxMjGbXJtF4N6nUBaSZCaRagc7adIeK+4EpWmOji/JdsqWdywyW kV607be32iUpox4aa/SDq4IzP5bbP7vjRqpPs9u67oJqWmIbMJEysAiRiVk9gB6zG8MNhmlfkU2 7YWztm/xIOzRhAfO67SIs2wO4Yx7y5rPvVlBPpaw9KDeN5PP3jEh0c9EowxDcLyA77J9ZKYdTsE LK6dbqwJmkYGtcQL8FMSsrJ1IxI6QU43pSxJGLVqjCO6v5u9Zv6TWzpVqOdg6ncJUpj4qq8m+R+ SHEiRitazeOgsRAhM4OxgXs5FfRq9S6DJ3ss11KPetaHmvgCK44TdnJEbwqA45ZlAjNaaM5lLAT +85oRtj1 On Tue, Aug 26, 2025 at 03:12:08PM +0200, David Hildenbrand wrote: > On 12.08.25 17:44, Lorenzo Stoakes wrote: > > 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. > > > > Signed-off-by: Lorenzo Stoakes > > --- > > include/linux/mm_types.h | 13 ++++++++++--- > > kernel/fork.c | 7 +++++-- > > 2 files changed, 15 insertions(+), 5 deletions(-) > > > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > > index 38b3fa927997..25577ab39094 100644 > > --- a/include/linux/mm_types.h > > +++ b/include/linux/mm_types.h > > @@ -1820,16 +1820,23 @@ enum { > > #define MMF_TOPDOWN 31 /* mm searches top down by default */ > > #define MMF_TOPDOWN_MASK _BITUL(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); > > Why not use the magic number 32 you are mentioning in the comment? :) Meh I mean UINT_MAX works as a good 'any bit' mask and this will work on both 32-bit and 64-bit systems. > > static_assert((u32)MMF_INIT_LEGACY_MASK != MMF_INIT_LEGACY_MASK); On 32-bit that'd not work would it? Kinda the point here is that the issue would get picked up on either. I think with the comment above it's fine as-is! :) > > > + > > +/* > > + * Initialise legacy flags according to masks, propagating selected flags on > > + * fork. Further flag manipulation can be performed by the caller. > > It's weird not reading "initialize", but I am afraid the kernel is already > tainted :P > > t14s: ~/git/linux nth_page $ git grep "initialise" | wc -l > 1778 > t14s: ~/git/linux nth_page $ git grep "initialize" | wc -l > 22043 British English in the kernel will survive if I have anything to do with it ;) > > Besides the assert simplification > > Acked-by: David Hildenbrand Thanks! > > -- > Cheers > > David / dhildenb >