Move TLB-handling code to the cpu pkg

kernel/cpu/cpu_amd64.go

@@ -0,0 +1,11 @@
+package cpu
+
+// FlushTLBEntry flushes a TLB entry for a particular virtual address.
+func FlushTLBEntry(virtAddr uintptr)
+
+// SwitchPDT sets the root page table directory to point to the specified
+// physical address and flushes the TLB.
+func SwitchPDT(pdtPhysAddr uintptr)
+
+// ActivePDT returns the physical address of the currently active page table.
+func ActivePDT() uintptr

kernel/cpu/cpu_amd64.s

@@ -0,0 +1,16 @@
+#include "textflag.h"
+
+TEXT ·FlushTLBEntry(SB),NOSPLIT,$0
+	INVLPG virtAddr+0(FP)
+	RET
+
+TEXT ·SwitchPDT(SB),NOSPLIT,$0
+	// loading CR3 also triggers a TLB flush
+	MOVQ pdtPhysAddr+0(FP), CR3
+	RET
+
+TEXT ·ActivePDT(SB),NOSPLIT,$0
+	MOVQ CR3, AX
+	MOVQ AX, ret+0(FP)
+	RET
+