Kernel/Memory: Make has_been_{r,w,x} flags clearly being set

Before of this change, actually setting the m_access to contain the
HasBeen{Readeable,Writable,Executable} bits was done by the method of
Region set_access_bit which added ORing with (access << 4) when enabling
a certain access bit to achieve this.

Now this is changed and when calling set_{readeable,writable,executable}
methods, they will set an appropriate SetOnce flag that could be checked
later.

Kernel/Memory/Region.h

@@ -43,9 +43,6 @@ class Region final
         Read = 1,
         Write = 2,
         Execute = 4,
-        HasBeenReadable = 16,
-        HasBeenWritable = 32,
-        HasBeenExecutable = 64,
         ReadOnly = Read,
         ReadWrite = Read | Write,
         ReadWriteExecute = Read | Write | Execute,
@@ -69,9 +66,9 @@ class Region final
     [[nodiscard]] bool is_writable() const { return (m_access & Access::Write) == Access::Write; }
     [[nodiscard]] bool is_executable() const { return (m_access & Access::Execute) == Access::Execute; }
 
-    [[nodiscard]] bool has_been_readable() const { return (m_access & Access::HasBeenReadable) == Access::HasBeenReadable; }
-    [[nodiscard]] bool has_been_writable() const { return (m_access & Access::HasBeenWritable) == Access::HasBeenWritable; }
-    [[nodiscard]] bool has_been_executable() const { return (m_access & Access::HasBeenExecutable) == Access::HasBeenExecutable; }
+    [[nodiscard]] bool has_been_readable() const { return m_has_been_readable.was_set(); }
+    [[nodiscard]] bool has_been_writable() const { return m_has_been_writable.was_set(); }
+    [[nodiscard]] bool has_been_executable() const { return m_has_been_executable.was_set(); }
 
     [[nodiscard]] bool is_cacheable() const { return m_cacheable; }
     [[nodiscard]] StringView name() const { return m_name ? m_name->view() : StringView {}; }
@@ -185,9 +182,24 @@ class Region final
 
     [[nodiscard]] size_t cow_pages() const;
 
-    void set_readable(bool b) { set_access_bit(Access::Read, b); }
-    void set_writable(bool b) { set_access_bit(Access::Write, b); }
-    void set_executable(bool b) { set_access_bit(Access::Execute, b); }
+    void set_readable(bool b)
+    {
+        set_access_bit(Access::Read, b);
+        if (b)
+            m_has_been_readable.set();
+    }
+    void set_writable(bool b)
+    {
+        set_access_bit(Access::Write, b);
+        if (b)
+            m_has_been_writable.set();
+    }
+    void set_executable(bool b)
+    {
+        set_access_bit(Access::Execute, b);
+        if (b)
+            m_has_been_executable.set();
+    }
 
     void unsafe_clear_access() { m_access = Region::None; }
 
@@ -221,7 +233,7 @@ class Region final
     void set_access_bit(Access access, bool b)
     {
         if (b)
-            m_access |= access | (access << 4);
+            m_access |= access;
         else
             m_access &= ~access;
     }
@@ -250,6 +262,9 @@ class Region final
     bool m_mmapped_from_writable : 1 { false };
 
     SetOnce m_immutable;
+    SetOnce m_has_been_readable;
+    SetOnce m_has_been_writable;
+    SetOnce m_has_been_executable;
 
     IntrusiveRedBlackTreeNode<FlatPtr, Region, RawPtr<Region>> m_tree_node;
     IntrusiveListNode<Region> m_vmobject_list_node;