Kernel: Implement MemoryRegion pinning

This allows process to pin a MemoryRegion into users memory space for
syscall duration without allowing user to munmap the region.

kernel/include/kernel/Memory/MemoryRegion.h

@@ -3,8 +3,7 @@
 #include <BAN/UniqPtr.h>
 #include <kernel/Memory/PageTable.h>
 #include <kernel/Memory/Types.h>
-
-#include <stddef.h>
+#include <kernel/ThreadBlocker.h>
 
 namespace Kernel
 {
@@ -42,6 +41,10 @@ namespace Kernel
 		size_t virtual_page_count() const { return BAN::Math::div_round_up<size_t>(m_size, PAGE_SIZE); }
 		size_t physical_page_count() const { return m_physical_page_count; }
 
+		void pin() { m_pinned_count++; }
+		void unpin() { if (--m_pinned_count == 0) m_pinned_blocker.unblock(); }
+		void wait_not_pinned() { while (m_pinned_count) m_pinned_blocker.block_with_timeout_ms(100); }
+
 		virtual BAN::ErrorOr<void> msync(vaddr_t, size_t, int) = 0;
 
 		// Returns error if no memory was available
@@ -64,6 +67,9 @@ namespace Kernel
 		const PageTable::flags_t m_flags;
 		vaddr_t m_vaddr { 0 };
 		size_t m_physical_page_count { 0 };
+
+		BAN::Atomic<size_t> m_pinned_count { 0 };
+		ThreadBlocker m_pinned_blocker;
 	};
 
 }

kernel/kernel/Memory/MemoryRegion.cpp

@@ -13,6 +13,7 @@ namespace Kernel
 
 	MemoryRegion::~MemoryRegion()
 	{
+		ASSERT(m_pinned_count == 0);
 		if (m_vaddr)
 			m_page_table.unmap_range(m_vaddr, m_size);
 	}

kernel/kernel/Process.cpp

@@ -1806,7 +1806,10 @@ namespace Kernel
 			const vaddr_t region_s = region->vaddr();
 			const vaddr_t region_e = region->vaddr() + region->size();
 			if (vaddr <= region_s && region_e <= vaddr + len)
+			{
+				region->wait_not_pinned();
 				m_mapped_regions.remove(i--);
+			}
 			else if (region->overlaps(vaddr, len))
 				dwarnln("TODO: partial region munmap");
 		}