On Tue, Aug 26, 2025 at 03:05:27PM +0200, David Hildenbrand wrote: > On 12.08.25 17:44, Lorenzo Stoakes wrote: > > There is an issue with the mask declarations in linux/mm_types.h, which > > naively do (1 << bit) operations. Unfortunately this results in the 1 being > > defaulted as a signed (32-bit) integer. > > > > When the compiler expands the MMF_INIT_MASK bitmask it comes up with: > > > > (((1 << 2) - 1) | (((1 << 9) - 1) << 2) | (1 << 24) | (1 << 28) | (1 << 30) > > | (1 << 31)) > > > > Which overflows the signed integer to -788,527,105. Implicitly casting this > > to an unsigned integer results in sign-expansion, and thus this value > > becomes 0xffffffffd10007ff, rather than the intended 0xd10007ff. > > > > While we're limited to a maximum of 32 bits in mm->flags, this isn't an > > issue as the remaining bits being masked will always be zero. > > > > However, now we are moving towards having more bits in this flag, this > > becomes an issue. > > > > Simply resolve this by using the _BITUL() helper to cast the shifted value > > to an unsigned long. > > Hmm, I thought BIT() should be used and would just fine? Sure.
