Merge branch 'master' into chenyh/amd64
Fix serial port on AMD64 hw

Signed-off-by: Chen Yuheng <chyh1990@gmail.com>
Implement RefCache and use percpu runqueue

About RefCache, see MIT's RadixVM paper

Signed-off-by: Chen Yuheng <chyh1990@gmail.com>
naive tlb shootdown and timerlist lock

Signed-off-by: Chen Yuheng <chyh1990@gmail.com>
Pin kernel thread to CPU

Signed-off-by: Yuheng Chen <chyh1990@gmail.com>
Signed-off-by: Chen Yuheng <chyh1990@gmail.com>