ladybird/Kernel/VM/PhysicalPage.h

/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include <AK/NonnullRefPtr.h>
#include <Kernel/Arch/i386/CPU.h>
#include <Kernel/Assertions.h>
#include <Kernel/Heap/SlabAllocator.h>
#include <Kernel/PhysicalAddress.h>

namespace Kernel {

class PhysicalPage {
    friend class MemoryManager;
    friend class PageDirectory;
    friend class VMObject;

    MAKE_SLAB_ALLOCATED(PhysicalPage);
    AK_MAKE_NONMOVABLE(PhysicalPage);

public:
    PhysicalAddress paddr() const { return m_paddr; }

    void ref()
    {
        m_ref_count.fetch_add(1, AK::memory_order_acq_rel);
    }

    void unref()
    {
        if (m_ref_count.fetch_sub(1, AK::memory_order_acq_rel) == 1) {
            if (m_may_return_to_freelist)
                return_to_freelist();
            delete this;
        }
    }

    static NonnullRefPtr<PhysicalPage> create(PhysicalAddress, bool supervisor, bool may_return_to_freelist = true);

    u32 ref_count() const { return m_ref_count.load(AK::memory_order_consume); }

    bool is_shared_zero_page() const;

private:
    PhysicalPage(PhysicalAddress paddr, bool supervisor, bool may_return_to_freelist = true);
    ~PhysicalPage() { }

    void return_to_freelist() const;

    Atomic<u32> m_ref_count { 1 };
    bool m_may_return_to_freelist { true };
    bool m_supervisor { false };
    PhysicalAddress m_paddr;
};

}