I'm using 32bit linux 4.1.8 with Yocto environment on the P4080DS SoC and noticed that the last 256MB of the 32bit addresses space are reserved for some purpose.
/*The amount of lowmem must be within 0xF0000000 - KERNELBASE. */
# if (CONFIG_LOWMEM_SIZE > (0xF0000000 - PAGE_OFFSET))
# error "You must adjust CONFIG_LOWMEM_SIZE or CONFIG_KERNEL_START"
I wanted to use addresses 0XF0000000 - 0XFFFFFFFF for lowmemory but I can't.
What are they reserved for? maybe vmalloc area? and is it possible to resize this reserved area (shrink it)?