Allow page table copying and unmapping

Lots of rearranging in page_manager as well, moving constants out as
well as helper structs.

src/kernel/page_table.h

@@ -0,0 +1,63 @@
+#pragma once
+/// \file page_table.h
+/// Helper structures for dealing with page tables.
+
+#include <stdint.h>
+#include "kernel_memory.h"
+
+class page_manager;
+
+/// Struct to allow easy accessing of a memory page being used as a page table.
+struct page_table
+{
+	enum class level : unsigned { pml4, pdp, pd, pt };
+	inline static level deeper(level l) {
+		return static_cast<level>(static_cast<unsigned>(l) + 1);
+	}
+
+	uint64_t entries[512];
+
+	inline page_table * get(int i, uint16_t *flags = nullptr) const {
+		uint64_t entry = entries[i];
+		if ((entry & 0x1) == 0) return nullptr;
+		if (flags) *flags = entry & 0xfffull;
+		return reinterpret_cast<page_table *>((entry & ~0xfffull) + memory::page_offset);
+	}
+
+	inline void set(int i, page_table *p, uint16_t flags) {
+		entries[i] = (reinterpret_cast<uint64_t>(p) - memory::page_offset) | (flags & 0xfff);
+	}
+
+	inline bool is_present(int i) const { return (entries[i] & 0x1) == 0x1; }
+
+	inline bool is_large_page(level l, int i) const {
+		return
+			(l == level::pdp || l == level::pd) &&
+			(entries[i] & 0x80) == 0x80;
+	}
+
+	void dump(
+		level lvl = level::pml4,
+		bool recurse = true);
+};
+
+
+/// Helper struct for computing page table indices of a given address.
+struct page_table_indices
+{
+	page_table_indices(uint64_t v = 0);
+
+	uintptr_t addr() const;
+
+	inline operator uintptr_t() const { return addr(); }
+
+	/// Get the index for a given level of page table.
+	uint64_t & operator[](int i) { return index[i]; }
+	uint64_t operator[](int i) const { return index[i]; }
+	uint64_t & operator[](page_table::level i) { return index[static_cast<unsigned>(i)]; }
+	uint64_t operator[](page_table::level i) const { return index[static_cast<unsigned>(i)]; }
+	uint64_t index[4]; ///< Indices for each level of tables.
+};
+
+bool operator==(const page_table_indices &l, const page_table_indices &r);
+