stos: hal: Implement HalMmuForkVas()

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

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

@@ -187,6 +187,39 @@ MmuExtractLevel(MMU_VAS *Vas, UPTR Vma, PAGE_LEVEL Level, BOOLEAN Alloc)
     return PageMap;
 }
 
+ST_STATUS
+HalMmuForkVas(MMU_VAS *Old, MMU_VAS *NewResult)
+{
+    UPTR *OldVma, *NewVma;
+    UPTR NewPma;
+    MM_PFN NewPfn;
+
+    if (Old == NULL || NewResult == NULL) {
+        return STATUS_INVALID_PARAM;
+    }
+
+    NewPfn = MmRequestFrame();
+    if (NewPfn == 0) {
+        return STATUS_NO_MEMORY;
+    }
+
+    NewPma = NewPfn << LOG2_PAGESIZE;
+    NewVma = PMA_TO_VMA(NewPma);
+    OldVma = PMA_TO_VMA((Old->Cr3 & PTE_ADDR_MASK));
+
+    /* Start breeding the new VAS~ Fill it deep~ */
+    for (USHORT Off = 0; Off < 512; ++Off) {
+        if (Off < 256) {
+            NewVma[Off] = 0;
+        } else {
+            NewVma[Off] = OldVma[Off];
+        }
+    }
+
+    NewResult->Cr3 = NewPma;
+    return STATUS_SUCCESS;
+}
+
 VOID
 HalMmuReadVas(MMU_VAS *Result)
 {

paw/stos/head/hal/mmu.h

@@ -36,6 +36,19 @@ VOID HalMmuReadVas(MMU_VAS *Result);
  */
 VOID HalMmuWriteVas(MMU_VAS *Vas);
 
+/*
+ * When starting other cute slut critter processes, we need a fresh
+ * VAS with the lower half gone so that it can be re-populated properly
+ * for user processes.
+ *
+ * This function does not breed the CR3 register and you'll manually
+ * need to do so with HalMmuWriteVas()
+ *
+ * @Old:        Old VAS to fork
+ * @NewResult:  New result is written here
+ */
+ST_STATUS HalMmuForkVas(MMU_VAS *Old, MMU_VAS *NewResult);
+
 /*
  * Map a single page of memory
  *