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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: iam4oyzbmwr7sxfx3wm95zjgos8puzio X-Rspam-User: X-Rspamd-Queue-Id: 3E4391C0012 X-Rspamd-Server: rspam01 X-HE-Tag: 1756218507-437144 X-HE-Meta: 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 BVmgPzD+ dv0OiKC1RFMdiajfbS83xlnUJdx1sJYZBpW6SHeBB81u9x1WQg++RFiEqKRLkuIjB7y5NZTnxuV7ebnZ/AP1SfPzBbOqLnPxoBtZawETVGR1WTh/PB2X+YFgILHfkMymAd2E7uu1amac87b6epExkO1SawhObBZ7SjdYsYSrl/mw/MpQwz9ikrLEiu6VIgudGdp2Mf/hbYSL9SpvVuxHt0zYQqjfGkd6kVquUnEWlpjixIOIab5OUN5q7yWvnLPPYJLx9tpS071ljQT28/5m7OqlPif+rj2AZBun1/Q5kDGTRzY8dHJ0IKmoALCxuzt0vqh71LQwHdqIY+D6iqNOWziBbBAlT8frhWr0zWLKkc84NLpfeWbCGmLgXj/7JaXsGCLabBpDDseYxEGPpS40yPHwls526ldeGyTsyHcMl8BHmSTaqOQj97wXjHsODGiSxXIVkVuz+qUGvi/I= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 26.08.25 16:21, Lorenzo Stoakes wrote: > 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? On 32bit, BIT(32) would exceed the shift width of unsigned long -> undefined behavior. The compiler should naturally complain. -- Cheers David / dhildenb