While working on the HugeTLB Vmemmap Optimization (HVO) generalization, Sashiko reported that memmap_init_zone_device() could be asked to initialize struct pages with a large-page order for a physical range that was not naturally aligned to that order.
Following the Device DAX call path confirmed that the condition was reachable. Device DAX range validation checks the range size, but not its start address. An unaligned range can therefore reach memmap_init_zone_device() after the device binds, and a subsequent write to a userspace mapping may trigger a kernel panic. With the help of an LLM, I was able to reproduce the failure. The automatic resize path has a related problem. It can split an aligned size request across arbitrary free gaps, consume an unaligned fragment, and leave the resize partially applied when a later allocation fails. This series validates both the start and size of every Device DAX range and makes automatic resize account only for usable aligned space. It also fixes the mapping sysfs attribute to propagate validation failures instead of reporting success without allocating the requested range. Muchun Song (2): dax/bus: fix Device DAX range alignment validation dax/bus: fix mapping attribute error reporting drivers/dax/bus.c | 144 +++++++++++++++++++++++++++++++++++----------- 1 file changed, 109 insertions(+), 35 deletions(-) base-commit: 1a1de54f7369cd2b5bac0f265910e60ad3a6b4c3 -- 2.54.0
