stos/amd64: cpu: Save KPCR in IA32_GS_BASE

Signed-off-by: Chloe M. <chloe@mensia.org>

paw/stos/arch/amd64/cpu/init.c

@@ -13,6 +13,7 @@
 #include <ke/knot.h>
 #include <machine/cpuid.h>
 #include <machine/idt.h>
+#include <machine/msr.h>
 #include <stdef.h>
 
 #define DTRACE(Fmt, ...) \
@@ -132,6 +133,9 @@ HalKpcrP1Init(KPCR *Kpcr)
         : "r" ((UQUAD)IRQL_PASSIVE)
         : "memory"
     );
+
+    /* Save the current KPCR */
+    MdWrmsr(IA32_GS_BASE, (UPTR)Kpcr);
 }
 
 VOID
@@ -152,3 +156,19 @@ HalKpcrP2Init(KPCR *Kpcr)
         );
     }
 }
+
+KPCR *
+HalKpcrCurrent(VOID)
+{
+    KPCR *Kpcr;
+
+    Kpcr = (KPCR *)MdRdmsr(IA32_GS_BASE);
+    if (Kpcr == NULL) {
+        KeKnot(
+            KNOT_UNBOUND_RSRC,
+            "current kpcr is NULL\n"
+        );
+    }
+
+    return Kpcr;
+}

paw/stos/head/hal/kpcr.h

@@ -41,4 +41,10 @@ VOID HalKpcrP1Init(KPCR *Kpcr);
  */
 VOID HalKpcrP2Init(KPCR *Kpcr);
 
+/*
+ * Obtain the KPCR for the current processor, it is never to
+ * be of a NULL value.
+ */
+KPCR *HalKpcrCurrent(VOID);
+
 #endif  /* !_HAL_KPCR_H_ */