RISCV_L3_SHIFT
l3_index = (va - vm->hdr.kernbase) >> RISCV_L3_SHIFT;
a = (l3 >> RISCV_PTE_PPN0_S) << RISCV_L3_SHIFT;
va = vm->hdr.kernbase + (pteindex << RISCV_L3_SHIFT);
pa = (pte >> RISCV_PTE_PPN0_S) << RISCV_L3_SHIFT;
_Static_assert(L3_SHIFT == RISCV_L3_SHIFT, "L3_SHIFT mismatch");