stos: hal: Add virtual address space helpers

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

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

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description:  AMD64 MMU management
+ * Author:       Chloe M.
+ */
+
+#include <hal/mmu.h>
+#include <machine/vas.h>
+#include <stdef.h>
+
+VOID
+HalMmuReadVas(MMU_VAS *Result)
+{
+    if (Result == NULL) {
+        return;
+    }
+
+    ASMV(
+        "mov %%cr3, %0"
+        : "=r" (Result->Cr3)
+        :
+        : "memory"
+    );
+}
+
+VOID
+HalMmuWriteVas(MMU_VAS *Vas)
+{
+    if (Vas == NULL) {
+        return;
+    }
+
+    ASMV(
+        "mov %0, %%cr3"
+        :
+        : "r" (Vas->Cr3)
+        : "memory"
+    );
+}

paw/stos/head/arch/amd64/vas.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description:  MD virtual address space
+ * Author:       Chloe M.
+ */
+
+#ifndef _MACHINE_VAS_H_
+#define _MACHINE_VAS_H_ 1
+
+#include <stdef.h>
+
+/*
+ * Represents a virtual address space
+ *
+ * @Cr3: Control register 3 value
+ */
+typedef struct {
+    UPTR Cr3;
+} MMU_VAS;
+
+#endif  /* !_MACHINE_VAS_H_ */

paw/stos/head/hal/mmu.h

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description:  MMU HAL layer
+ * Author:       Chloe M.
+ */
+
+#ifndef _HAL_MMU_H_
+#define _HAL_MMU_H_ 1
+
+#include <stdef.h>
+#include <machine/vas.h>
+
+/*
+ * Read the current virtual address space
+ *
+ * @Result: Result is written here
+ */
+VOID HalMmuReadVas(MMU_VAS *Result);
+
+/*
+ * Write a new virtual address space
+ *
+ * @Vas: Virtual address space to write
+ */
+VOID HalMmuWriteVas(MMU_VAS *Vas);
+
+#endif  /* !_HAL_MMU_H_ */