feat: add page table

kernel/include/memory/pagetable.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include "memory/pointer.h"
+#include "util/optional.h"
+
+struct PageTable {
+    struct flags_t {
+        enum class granularity_t : uint8_t {
+            page_4KiB,
+            page_2MiB,
+            page_1GiB,
+        };
+
+        bool writeable : 1;            // allow writes
+        bool user_accessible : 1;      // allow ring-3 access
+        bool write_through : 1;        // write-through instead of write-back
+        bool cache_disabled : 1;       // uncached (MMIO)
+        bool execute_disabled : 1;     // forbid instruction fetch
+        bool global : 1;               // keep in TLB across CR3 switches
+        granularity_t granularity : 2; // mapping size
+    };
+    struct info_t {
+        flags_t flags;
+        paddr_t address;
+    };
+
+    static PageTable fromCurrent();
+
+    void activate();
+    bool map(void* vaddress, paddr_t paddress, flags_t flags);
+    void unmap(void* vaddress);
+    optional<info_t> get(void* vaddress);
+
+private:
+    paddr_t l4;
+};