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;
+};

kernel/include/memory/pointer.h

@@ -3,6 +3,7 @@
 #include "util/number.h"
 
 constexpr uint64_t high_base = 0xFFFF800000000000;
+constexpr uint64_t uncached_base = high_base + (uint64_t{1} << 38);
 
 #define read_symbol(symbol)                                                                                            \
     []() {                                                                                                             \
@@ -18,6 +19,11 @@ struct paddr_t {
     T* access() {
         return reinterpret_cast<T*>(address + high_base);
     }
+
+    template<typename T>
+    T* access_uc() {
+        return reinterpret_cast<T*>(address + uncached_base);
+    }
 };
 
 inline void* operator new(size_t, void* p) {