RISCV_PTE_PPN0_S
a = (l3 >> RISCV_PTE_PPN0_S) << RISCV_L3_SHIFT;
pa = (pte >> RISCV_PTE_PPN0_S) << RISCV_L3_SHIFT;
_Static_assert(PTE_PPN0_S == RISCV_PTE_PPN0_S, "PTE_PPN0_S mismatch");