mm: vmalloc: WARN_ON if mapping size is not PAGE_SIZE aligned

mm: vmalloc: WARN_ON if mapping size is not PAGE_SIZE aligned

In mm/vmalloc.c, the function vmap_pte_range() assumes that the mapping
size is aligned to PAGE_SIZE.  If this assumption is violated, the loop
will become infinite because the termination condition (`addr != end`)
will never be met.  This can lead to overwriting other VA ranges and/or
random pages physically follow the page table.

It's the caller's responsibility to ensure that the mapping size is
aligned to PAGE_SIZE.  However, the memory corruption is hard to root
cause.  To identify the programming error in the caller easier, check
whether the mapping size is PAGE_SIZE aligned with WARN_ON_ONCE().

[yadong.qi@linux.alibaba.com: fix uninitialized value issue]
  Closes: https://lore.kernel.org/r/202510110050.VG9YKMRK-lkp@intel.com/
Link: https://lkml.kernel.org/r/20251010014311.1689-1-yadong.qi@linux.alibaba.com
Signed-off-by: Yadong Qi <yadong.qi@linux.alibaba.com>
Reviewed-by: Huang Ying <ying.huang@linux.alibaba.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>