Kernel: Implement new abstract MemoryRegion

MemoryBackedRegion now inherits from this and is used for private
anonymous mappigs. This will make shared mappings and file backed
mappings much easier to implement.

kernel/kernel/Memory/MemoryBackedRegion.cpp

@@ -0,0 +1,124 @@
+#include <kernel/Memory/Heap.h>
+#include <kernel/Memory/MemoryBackedRegion.h>
+#include <kernel/LockGuard.h>
+
+namespace Kernel
+{
+
+	BAN::ErrorOr<BAN::UniqPtr<MemoryBackedRegion>> MemoryBackedRegion::create(PageTable& page_table, size_t size, AddressRange address_range, Type type, PageTable::flags_t flags)
+	{
+		ASSERT(type == Type::PRIVATE);
+
+		auto* region_ptr = new MemoryBackedRegion(page_table, size, type, flags);
+		if (region_ptr == nullptr)
+			return BAN::Error::from_errno(ENOMEM);
+		auto region = BAN::UniqPtr<MemoryBackedRegion>::adopt(region_ptr);
+
+		TRY(region->initialize(address_range));
+
+		return region;
+	}
+
+	MemoryBackedRegion::MemoryBackedRegion(PageTable& page_table, size_t size, Type type, PageTable::flags_t flags)
+		: MemoryRegion(page_table, size, type, flags)
+	{
+	}
+
+	MemoryBackedRegion::~MemoryBackedRegion()
+	{
+		ASSERT(m_type == Type::PRIVATE);
+
+		size_t needed_pages = BAN::Math::div_round_up<size_t>(m_size, PAGE_SIZE);
+		for (size_t i = 0; i < needed_pages; i++)
+		{
+			paddr_t paddr = m_page_table.physical_address_of(m_vaddr + i * PAGE_SIZE);
+			if (paddr != 0)
+				Heap::get().release_page(paddr);
+		}
+	}
+
+	BAN::ErrorOr<bool> MemoryBackedRegion::allocate_page_containing(vaddr_t address)
+	{
+		ASSERT(m_type == Type::PRIVATE);
+
+		ASSERT(contains(address));
+
+		// Check if address is already mapped
+		vaddr_t vaddr = address & PAGE_ADDR_MASK;
+		if (m_page_table.physical_address_of(vaddr) != 0)
+			return false;
+		
+		// Map new physcial page to address
+		paddr_t paddr = Heap::get().take_free_page();
+		if (paddr == 0)
+			return BAN::Error::from_errno(ENOMEM);
+		m_page_table.map_page_at(paddr, vaddr, m_flags);
+
+		// Zero out the new page
+		if (&PageTable::current() == &m_page_table)
+			memset((void*)vaddr, 0x00, PAGE_SIZE);
+		else
+		{
+			LockGuard _(PageTable::current());
+			ASSERT(PageTable::current().is_page_free(0));
+
+			PageTable::current().map_page_at(paddr, 0, PageTable::Flags::ReadWrite | PageTable::Flags::Present);
+			memset((void*)0, 0x00, PAGE_SIZE);
+			PageTable::current().unmap_page(0);
+		}
+
+		return true;
+	}
+
+	BAN::ErrorOr<BAN::UniqPtr<MemoryRegion>> MemoryBackedRegion::clone(PageTable& new_page_table)
+	{
+		ASSERT(&PageTable::current() == &m_page_table);
+
+		auto result = TRY(MemoryBackedRegion::create(new_page_table, m_size, { .start = m_vaddr, .end = m_vaddr + m_size }, m_type, m_flags));
+
+		for (size_t offset = 0; offset < m_size; offset += PAGE_SIZE)
+		{
+			paddr_t paddr = m_page_table.physical_address_of(m_vaddr + offset);
+			if (paddr == 0)
+				continue;
+			TRY(result->copy_data_to_region(offset, (const uint8_t*)(m_vaddr + offset), PAGE_SIZE));
+		}
+		
+		return BAN::UniqPtr<MemoryRegion>(BAN::move(result));
+	}
+
+	BAN::ErrorOr<void> MemoryBackedRegion::copy_data_to_region(size_t offset_into_region, const uint8_t* buffer, size_t buffer_size)
+	{
+		ASSERT(offset_into_region + buffer_size <= m_size);
+
+		size_t written = 0;
+		while (written < buffer_size)
+		{
+			vaddr_t write_vaddr = m_vaddr + offset_into_region + written;
+			vaddr_t page_offset = write_vaddr % PAGE_SIZE;
+			size_t bytes = BAN::Math::min<size_t>(buffer_size - written, PAGE_SIZE - page_offset);
+
+			TRY(allocate_page_containing(write_vaddr));
+
+			if (&PageTable::current() == &m_page_table)
+				memcpy((void*)write_vaddr, (void*)(buffer + written), bytes);
+			else
+			{
+				paddr_t paddr = m_page_table.physical_address_of(write_vaddr & PAGE_ADDR_MASK);
+				ASSERT(paddr);
+
+				LockGuard _(PageTable::current());
+				ASSERT(PageTable::current().is_page_free(0));
+
+				PageTable::current().map_page_at(paddr, 0, PageTable::Flags::ReadWrite | PageTable::Flags::Present);
+				memcpy((void*)page_offset, (void*)(buffer + written), bytes);
+				PageTable::current().unmap_page(0);
+			}
+
+			written += bytes;
+		}
+
+		return {};
+	}
+
+}