2 files changed, 24 insertions, 3 deletions

diff --git a/src/common/page_table.cpp b/src/common/page_table.cpp
index 69b7abc54..566b57b62 100644
--- a/src/common/page_table.cpp
+++ b/src/common/page_table.cpp
@@ -16,7 +16,6 @@ void PageTable::Resize(std::size_t address_space_width_in_bits) {
 
     pointers.resize(num_page_table_entries);
     attributes.resize(num_page_table_entries);
-    backing_addr.resize(num_page_table_entries);
 
     // The default is a 39-bit address space, which causes an initial 1GB allocation size. If the
     // vector size is subsequently decreased (via resize), the vector might not automatically
@@ -25,6 +24,17 @@ void PageTable::Resize(std::size_t address_space_width_in_bits) {
 
     pointers.shrink_to_fit();
     attributes.shrink_to_fit();
+}
+
+BackingPageTable::BackingPageTable(std::size_t page_size_in_bits) : PageTable{page_size_in_bits} {}
+
+BackingPageTable::~BackingPageTable() = default;
+
+void BackingPageTable::Resize(std::size_t address_space_width_in_bits) {
+    PageTable::Resize(address_space_width_in_bits);
+    const std::size_t num_page_table_entries = 1ULL
+                                               << (address_space_width_in_bits - page_size_in_bits);
+    backing_addr.resize(num_page_table_entries);
     backing_addr.shrink_to_fit();
 }
 
diff --git a/src/common/page_table.h b/src/common/page_table.h
index 8b8ff0bb8..dbc272ab7 100644
--- a/src/common/page_table.h
+++ b/src/common/page_table.h
@@ -76,9 +76,20 @@ struct PageTable {
      */
     std::vector<PageType> attributes;
 
-    std::vector<u64> backing_addr;
-
     const std::size_t page_size_in_bits{};
 };
 
+/**
+ * A more advanced Page Table with the ability to save a backing address when using it
+ * depends on another MMU.
+ */
+struct BackingPageTable : PageTable {
+    explicit BackingPageTable(std::size_t page_size_in_bits);
+    ~BackingPageTable();
+
+    void Resize(std::size_t address_space_width_in_bits);
+
+    std::vector<u64> backing_addr;
+};
+
 } // namespace Common