Question about flash allocation

Hi,

Why does CFI(or other flash memory) have to alloc amount of flash
memory size to the vmalloc area(such as PHYSMAP or PHYSMAP_OF)?
I wondered other devices seems to not allocating(e.g, most NAND flash,
flash on ARM, MIPS and so on). I don't know difference between my
board and other. Doesn't other devices need to allocate to vmalloc?

Thanks,
Mitsutaka