Kernel: Pull apart CPU.h

This does not add any functional changes

Kernel/Arch/x86/ScopedCritical.h

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+
+#include <Kernel/Arch/x86/Processor.h>
+
+namespace Kernel {
+
+class ScopedCritical {
+    AK_MAKE_NONCOPYABLE(ScopedCritical);
+
+public:
+    ScopedCritical()
+    {
+        enter();
+    }
+
+    ~ScopedCritical()
+    {
+        if (m_valid)
+            leave();
+    }
+
+    ScopedCritical(ScopedCritical&& from)
+        : m_prev_flags(exchange(from.m_prev_flags, 0))
+        , m_valid(exchange(from.m_valid, false))
+    {
+    }
+
+    ScopedCritical& operator=(ScopedCritical&& from)
+    {
+        if (&from != this) {
+            m_prev_flags = exchange(from.m_prev_flags, 0);
+            m_valid = exchange(from.m_valid, false);
+        }
+        return *this;
+    }
+
+    void leave()
+    {
+        VERIFY(m_valid);
+        m_valid = false;
+        Processor::current().leave_critical(m_prev_flags);
+    }
+
+    void enter()
+    {
+        VERIFY(!m_valid);
+        m_valid = true;
+        Processor::current().enter_critical(m_prev_flags);
+    }
+
+private:
+    u32 m_prev_flags { 0 };
+    bool m_valid { false };
+};
+
+}