A compound page of order N must start at a PFN aligned to 2^N pages. Therefore, a range used to initialize compound pages must start on a compound-page boundary and contain an integral number of compound pages.
Two recent Device DAX bugs were caused by ranges that violated this invariant, but neither was detected by memmap_init_zone_device(). Warn if the adjusted zone-device range violates this invariant so future violations are reported when the compound pages are initialized. Link: https://lore.kernel.org/r/[email protected] Link: https://lore.kernel.org/r/[email protected] Assisted-by: LLM Signed-off-by: Muchun Song <[email protected]> --- mm/mm_init.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/mm_init.c b/mm/mm_init.c index 4c17a892924d..01ced0553ce9 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1142,6 +1142,8 @@ void __ref memmap_init_zone_device(struct zone *zone, if (!nr_pages) return; + VM_WARN_ON(!IS_ALIGNED(start_pfn | nr_pages, pfns_per_compound)); + /* * Seed the reusable head-page template from the first real struct * page. The normal page-init and refcount helpers must operate on base-commit: 63562804f25cb5b6f5e4f5e3a9f0d1c3c6868596 -- 2.54.0
