stos: hal+amd64: Add helper to unmap single page

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

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

@@ -274,3 +274,25 @@ HalMmuMapSingle(MMU_VAS *Vas, UPTR Vma, UPTR Pma, USHORT Flags, MMU_PAGESIZE Pag
     MmuInvlpg(Vma);
     return STATUS_SUCCESS;
 }
+
+ST_STATUS
+HalMmuUnmapSingle(MMU_VAS *Vas, UPTR Vma, MMU_PAGESIZE PageSize)
+{
+    UPTR *PageTable;
+    USHORT Index;
+
+    if (Vas == NULL) {
+        return STATUS_INVALID_PARAM;
+    }
+
+    PageTable = MmuExtractLevel(Vas, Vma, PAGE_LEVEL_PML1, false);
+    if (PageTable == NULL) {
+        return STATUS_NOT_FOUND;
+    }
+
+    /* Unmap the page */
+    Index = MmuLevelIndex(Vma, PAGE_LEVEL_PML1);
+    PageTable[Index] = 0;
+    MmuInvlpg(Vma);
+    return STATUS_SUCCESS;
+}

paw/stos/head/hal/mmu.h

@@ -63,4 +63,13 @@ ST_STATUS HalMmuMapSingle(
     USHORT Flags, MMU_PAGESIZE PageSize
 );
 
+/*
+ * Unmap a single page of memory
+ *
+ * @Vas:        Virtual address space to unmap within
+ * @Vma:        Virtual address to unmap
+ * @PageSize:   Pagesize to unmap
+ */
+ST_STATUS HalMmuUnmapSingle(MMU_VAS *Vas, UPTR Vma, MMU_PAGESIZE PageSize);
+
 #endif  /* !_HAL_MMU_H_ */