Kernel: Implement bare boness DMA Region

This does nothing but allocate contiguous physical and virtual memory
and map it as CacheDisable. Also memory is automatically freed RAII style.

kernel/kernel/Memory/DMARegion.cpp

@@ -0,0 +1,46 @@
+#include <BAN/ScopeGuard.h>
+#include <kernel/Memory/DMARegion.h>
+#include <kernel/Memory/Heap.h>
+
+namespace Kernel
+{
+
+	BAN::ErrorOr<BAN::UniqPtr<DMARegion>> DMARegion::create(size_t size)
+	{
+		size_t needed_pages = BAN::Math::div_round_up<size_t>(size, PAGE_SIZE);
+
+		vaddr_t vaddr = PageTable::kernel().reserve_free_contiguous_pages(needed_pages, KERNEL_OFFSET);
+		if (vaddr == 0)
+			return BAN::Error::from_errno(ENOMEM);
+		BAN::ScopeGuard vaddr_guard([vaddr, size] { PageTable::kernel().unmap_range(vaddr, size); });
+
+		paddr_t paddr = Heap::get().take_free_contiguous_pages(needed_pages);
+		if (paddr == 0)
+			return BAN::Error::from_errno(ENOMEM);
+		BAN::ScopeGuard paddr_guard([paddr, needed_pages] { Heap::get().release_contiguous_pages(paddr, needed_pages); });
+
+		auto* region_ptr = new DMARegion(size, vaddr, paddr);
+		if (region_ptr == nullptr)
+			return BAN::Error::from_errno(ENOMEM);
+		
+		vaddr_guard.disable();
+		paddr_guard.disable();
+
+		PageTable::kernel().map_range_at(paddr, vaddr, size, PageTable::Flags::CacheDisable | PageTable::Flags::ReadWrite | PageTable::Flags::Reserved);
+
+		return BAN::UniqPtr<DMARegion>::adopt(region_ptr);
+	}
+
+	DMARegion::DMARegion(size_t size, vaddr_t vaddr, paddr_t paddr)
+		: m_size(size)
+		, m_vaddr(vaddr)
+		, m_paddr(paddr)
+	{ }
+
+	DMARegion::~DMARegion()
+	{
+		PageTable::kernel().unmap_range(m_vaddr, m_size);
+		Heap::get().release_contiguous_pages(m_vaddr, BAN::Math::div_round_up<size_t>(m_size, PAGE_SIZE));
+	}
+
+}