diff --git a/kernel/src/arch/riscv32/boot/trap.asm b/kernel/src/arch/riscv32/boot/trap.asm
index d4008266..37afaf11 100644
--- a/kernel/src/arch/riscv32/boot/trap.asm
+++ b/kernel/src/arch/riscv32/boot/trap.asm
@@ -13,7 +13,8 @@ _save_context:
     # save x registers except x2 (sp)
     sw x1, 1*4(sp)
     sw x3, 3*4(sp)
-    sw x4, 4*4(sp)
+    # tp(x4) = hartid. DON'T change.
+    # sw x4, 4*4(sp)
     sw x5, 5*4(sp)
     sw x6, 6*4(sp)
     sw x7, 7*4(sp)
@@ -73,7 +74,7 @@ _restore_context:
     # restore x registers except x2 (sp)
     lw x1, 1*4(sp)
     lw x3, 3*4(sp)
-    lw x4, 4*4(sp)
+    # lw x4, 4*4(sp)
     lw x5, 5*4(sp)
     lw x6, 6*4(sp)
     lw x7, 7*4(sp)
diff --git a/kernel/src/arch/riscv32/interrupt.rs b/kernel/src/arch/riscv32/interrupt.rs
index cee4bc17..bad1812e 100644
--- a/kernel/src/arch/riscv32/interrupt.rs
+++ b/kernel/src/arch/riscv32/interrupt.rs
@@ -42,7 +42,7 @@ pub unsafe fn restore(flags: usize) {
 #[no_mangle]
 pub extern fn rust_trap(tf: &mut TrapFrame) {
     use super::riscv::register::scause::{Trap, Interrupt as I, Exception as E};
-    trace!("Interrupt: {:?}", tf.scause.cause());
+    trace!("Interrupt @ CPU{}: {:?} ", super::cpu::id(), tf.scause.cause());
     match tf.scause.cause() {
         Trap::Interrupt(I::SupervisorSoft) => ipi(),
         Trap::Interrupt(I::SupervisorTimer) => timer(),
@@ -50,7 +50,6 @@ pub extern fn rust_trap(tf: &mut TrapFrame) {
         Trap::Exception(E::UserEnvCall) => syscall(tf),
         _ => ::trap::error(tf),
     }
-    ::trap::before_return();
     trace!("Interrupt end");
 }
 
diff --git a/kernel/src/arch/riscv32/mod.rs b/kernel/src/arch/riscv32/mod.rs
index c6ccc1c9..de43a259 100644
--- a/kernel/src/arch/riscv32/mod.rs
+++ b/kernel/src/arch/riscv32/mod.rs
@@ -26,6 +26,9 @@ pub extern fn rust_main(hartid: usize, dtb: usize, hart_mask: usize) -> ! {
     memory::init();
     timer::init();
 
+    ::process::init();
+    ::thread::spawn(::fs::shell);
+
     unsafe { cpu::start_others(hart_mask); }
     ::kmain();
 }
@@ -33,8 +36,7 @@ pub extern fn rust_main(hartid: usize, dtb: usize, hart_mask: usize) -> ! {
 fn others_main() -> ! {
     interrupt::init();
     timer::init();
-    cpu::send_ipi(0);
-    loop { }
+    ::kmain();
 }
 
 #[cfg(feature = "no_bbl")]
diff --git a/kernel/src/arch/x86_64/interrupt/handler.rs b/kernel/src/arch/x86_64/interrupt/handler.rs
index a0369a46..2b8b1889 100644
--- a/kernel/src/arch/x86_64/interrupt/handler.rs
+++ b/kernel/src/arch/x86_64/interrupt/handler.rs
@@ -97,7 +97,6 @@ pub extern fn rust_trap(tf: &mut TrapFrame) {
         T_DIVIDE | T_GPFLT | T_ILLOP => error(tf),
         _ => panic!("Unhandled interrupt {:x}", tf.trap_num),
     }
-    ::trap::before_return();
 }
 
 fn breakpoint() {
diff --git a/kernel/src/arch/x86_64/mod.rs b/kernel/src/arch/x86_64/mod.rs
index b9a57f89..b739925d 100644
--- a/kernel/src/arch/x86_64/mod.rs
+++ b/kernel/src/arch/x86_64/mod.rs
@@ -47,6 +47,9 @@ pub extern "C" fn _start(boot_info: &'static BootInfo) -> ! {
 
     driver::init();
 
+    ::process::init();
+    ::thread::spawn(::fs::shell);
+
     AP_CAN_INIT.store(true, Ordering::Relaxed);
 
     ::kmain();
diff --git a/kernel/src/lib.rs b/kernel/src/lib.rs
index b8614ecb..1e5d83cd 100644
--- a/kernel/src/lib.rs
+++ b/kernel/src/lib.rs
@@ -62,11 +62,6 @@ pub mod arch;
 pub mod arch;
 
 pub fn kmain() -> ! {
-    if arch::cpu::id() == 0 {
-        process::init();
-        thread::spawn(fs::shell);
-    }
-
     process::processor().run();
 
 //    thread::test::local_key();
diff --git a/kernel/src/trap.rs b/kernel/src/trap.rs
index 749a0b26..529fd203 100644
--- a/kernel/src/trap.rs
+++ b/kernel/src/trap.rs
@@ -11,9 +11,6 @@ pub fn timer() {
     }
 }
 
-pub fn before_return() {
-}
-
 pub fn error(tf: &TrapFrame) -> ! {
     error!("{:#x?}", tf);
     let pid = processor().pid();