On Thu, Apr 4, 2024 at 1:15 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, 4 Apr 2024 16:25:14 +0000 Frank van der Linden <fvdl@xxxxxxxxxx> wrote: > > > cma_init_reserved_mem uses IS_ALIGNED to check if the size > > represented by one bit in the cma allocation bitmask is > > aligned with CMA_MIN_ALIGNMENT_BYTES (pageblock size). > > > > However, this is too strict, as this will fail if > > order_per_bit > pageblock_order, which is a valid configuration. > > > > We could check IS_ALIGNED both ways, but since both numbers are > > powers of two, no check is needed at all. > > What are the userspace visible effects of this bug? None that I know of. This bug was exposed because I made the hugetlb code correctly pass the right order_per_bit argument (see the accompanying hugetlb cma fix), which then tripped this check when I backported it to an older kernel, passing an order of 30 (1G hugetlb page) as order_per_bit. This actually won't happen for 6.9-rc, since the (intended) order_per_bit was reduced to HUGETLB_PAGE_ORDER because of hugetlb page demotion. So, no user visible effects. However, if the other fix is going to be backported, this one is a prereq. - Frank
