KERN_VIRT_SIZE     29 arch/powerpc/include/asm/nohash/64/pgtable.h #define KERN_VIRT_SIZE	ASM_CONST(0x0000100000000000)
KERN_VIRT_SIZE     36 arch/riscv/include/asm/page.h #define KERN_VIRT_SIZE (-PAGE_OFFSET)