diff --git a/BOOT/ENVIRON/INC/mm.h b/BOOT/ENVIRON/INC/mm.h
index 1b77c9a..fea0b92 100644
--- a/BOOT/ENVIRON/INC/mm.h
+++ b/BOOT/ENVIRON/INC/mm.h
@@ -20,6 +20,7 @@ Abstract:
 
 #define MDL_OPERATION_FLAGS_TRUNCATE 0x00000002
 #define MDL_OPERATION_FLAGS_PHYSICAL 0x40000000
+#define MDL_OPERATION_FLAGS_VIRTUAL  0x80000000
 
 NTSTATUS
 MmFwGetMemoryMap (
diff --git a/BOOT/ENVIRON/LIB/MM/mmmd.c b/BOOT/ENVIRON/LIB/MM/mmmd.c
index 1a85251..492eeec 100644
--- a/BOOT/ENVIRON/LIB/MM/mmmd.c
+++ b/BOOT/ENVIRON/LIB/MM/mmmd.c
@@ -454,9 +454,60 @@ Return Value:
 
 
 {
+    BOOLEAN Mapped;
+    PMEMORY_DESCRIPTOR Descriptor;
+    PLIST_ENTRY ListEntry;
+    ULONGLONG FirstPage;
+
+    Mapped = FALSE;
+    if (Flags & MDL_OPERATION_FLAGS_VIRTUAL) {
+        if (Mdl->Type == MDL_TYPE_PHYSICAL) {
+            Mapped = TRUE;
+        }
+    } else {
+        //
+        // If the MDL is virtual, the
+        // virtual flag must be set.
+        //
+        if (Mdl->Type == MDL_TYPE_VIRTUAL) {
+            return NULL;
+        }
+    }
+
     //
-    // TODO: Implement this routine.
+    // Check if the cached descriptor is in range.
     //
+    if (!Mapped && Mdl->Current != NULL) {
+        Descriptor = (PMEMORY_DESCRIPTOR)Mdl->Current;
+        if (Page < Descriptor->FirstPage) {
+            ListEntry = Mdl->Head->Flink;
+        } else {
+            ListEntry = Mdl->Current;
+        }
+    } else {
+        ListEntry = Mdl->Head->Flink;
+    }
+
+    while (ListEntry != Mdl->Head) {
+        Descriptor = (PMEMORY_DESCRIPTOR)ListEntry;
+
+        if (Mapped) {
+            FirstPage = Descriptor->MappedFirstPage;
+        } else {
+            FirstPage = Descriptor->FirstPage;
+        }
+
+        //
+        // Check if this descriptor contains Page.
+        //
+        if ((!Mapped || FirstPage)
+            && Page >= FirstPage
+            && Page < FirstPage + Descriptor->PageCount) {
+            return Descriptor;
+        }
+
+        ListEntry = ListEntry->Flink;
+    }
 
     return NULL;
 }