kernel: implement cpu IDs and per-cpu variables

arch/x86_64/include/arch/msr.h

@@ -0,0 +1,12 @@
+#ifndef ARCH_MSR_H_
+#define ARCH_MSR_H_
+
+#include <stdint.h>
+
+#define MSR_GS_BASE 0xC0000101
+
+/* defined in cpu_ctrl.S */
+extern uint64_t rdmsr(uint32_t id);
+extern void wrmsr(uint32_t id, uint64_t val);
+
+#endif