Kernel/Memory: Introduce the SharedFramebufferVMObject class

This new type of VMObject will be used to coordinate switching safely
from graphical mode to text mode and vice-versa, by supplying a way to
remap all Regions that were created with this object, so mappings can be
changed according to the given state of system mode. This makes it quite
easy to give applications like WindowServer the feeling of having full
access to the framebuffer device from a DisplayConnector, but still keep
the Kernel in control to be able to safely switch to text console.

Kernel/Memory/SharedFramebufferVMObject.h

@@ -0,0 +1,94 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <Kernel/Forward.h>
+#include <Kernel/Memory/AllocationStrategy.h>
+#include <Kernel/Memory/AnonymousVMObject.h>
+#include <Kernel/Memory/MemoryManager.h>
+#include <Kernel/Memory/PageFaultResponse.h>
+#include <Kernel/PhysicalAddress.h>
+
+namespace Kernel::Memory {
+
+class SharedFramebufferVMObject final : public VMObject {
+public:
+    class FakeWritesFramebufferVMObject final : public VMObject {
+    public:
+        static ErrorOr<NonnullRefPtr<FakeWritesFramebufferVMObject>> try_create(Badge<SharedFramebufferVMObject>, SharedFramebufferVMObject const& parent_object);
+
+    private:
+        FakeWritesFramebufferVMObject(SharedFramebufferVMObject const& parent_object, FixedArray<RefPtr<PhysicalPage>>&& new_physical_pages)
+            : VMObject(move(new_physical_pages))
+            , m_parent_object(parent_object)
+        {
+        }
+        virtual StringView class_name() const override { return "FakeWritesFramebufferVMObject"sv; }
+        virtual ErrorOr<NonnullRefPtr<VMObject>> try_clone() override { return Error::from_errno(ENOTIMPL); }
+        virtual Span<RefPtr<PhysicalPage> const> physical_pages() const override { return m_parent_object->fake_sink_framebuffer_physical_pages(); }
+        virtual Span<RefPtr<PhysicalPage>> physical_pages() override { return m_parent_object->fake_sink_framebuffer_physical_pages(); }
+        NonnullRefPtr<SharedFramebufferVMObject> m_parent_object;
+    };
+
+    class RealWritesFramebufferVMObject final : public VMObject {
+    public:
+        static ErrorOr<NonnullRefPtr<RealWritesFramebufferVMObject>> try_create(Badge<SharedFramebufferVMObject>, SharedFramebufferVMObject const& parent_object);
+
+    private:
+        RealWritesFramebufferVMObject(SharedFramebufferVMObject const& parent_object, FixedArray<RefPtr<PhysicalPage>>&& new_physical_pages)
+            : VMObject(move(new_physical_pages))
+            , m_parent_object(parent_object)
+        {
+        }
+        virtual StringView class_name() const override { return "RealWritesFramebufferVMObject"sv; }
+        virtual ErrorOr<NonnullRefPtr<VMObject>> try_clone() override { return Error::from_errno(ENOTIMPL); }
+        virtual Span<RefPtr<PhysicalPage> const> physical_pages() const override { return m_parent_object->real_framebuffer_physical_pages(); }
+        virtual Span<RefPtr<PhysicalPage>> physical_pages() override { return m_parent_object->real_framebuffer_physical_pages(); }
+        NonnullRefPtr<SharedFramebufferVMObject> m_parent_object;
+    };
+
+    virtual ~SharedFramebufferVMObject() override = default;
+
+    static ErrorOr<NonnullRefPtr<SharedFramebufferVMObject>> try_create_for_physical_range(PhysicalAddress paddr, size_t size);
+    static ErrorOr<NonnullRefPtr<SharedFramebufferVMObject>> try_create_at_arbitrary_physical_range(size_t size);
+    virtual ErrorOr<NonnullRefPtr<VMObject>> try_clone() override { return Error::from_errno(ENOTIMPL); }
+
+    void switch_to_fake_sink_framebuffer_writes(Badge<Kernel::DisplayConnector>);
+    void switch_to_real_framebuffer_writes(Badge<Kernel::DisplayConnector>);
+
+    virtual Span<RefPtr<PhysicalPage> const> physical_pages() const override;
+    virtual Span<RefPtr<PhysicalPage>> physical_pages() override;
+
+    Span<RefPtr<PhysicalPage>> fake_sink_framebuffer_physical_pages();
+    Span<RefPtr<PhysicalPage> const> fake_sink_framebuffer_physical_pages() const;
+
+    Span<RefPtr<PhysicalPage>> real_framebuffer_physical_pages();
+    Span<RefPtr<PhysicalPage> const> real_framebuffer_physical_pages() const;
+
+    FakeWritesFramebufferVMObject const& fake_writes_framebuffer_vmobject() const { return *m_fake_writes_framebuffer_vmobject; }
+    FakeWritesFramebufferVMObject& fake_writes_framebuffer_vmobject() { return *m_fake_writes_framebuffer_vmobject; }
+
+    RealWritesFramebufferVMObject const& real_writes_framebuffer_vmobject() const { return *m_real_writes_framebuffer_vmobject; }
+    RealWritesFramebufferVMObject& real_writes_framebuffer_vmobject() { return *m_real_writes_framebuffer_vmobject; }
+
+private:
+    SharedFramebufferVMObject(FixedArray<RefPtr<PhysicalPage>>&& new_physical_pages, CommittedPhysicalPageSet, AnonymousVMObject& real_framebuffer_vmobject);
+
+    virtual StringView class_name() const override { return "SharedFramebufferVMObject"sv; }
+
+    ErrorOr<void> create_fake_writes_framebuffer_vm_object();
+    ErrorOr<void> create_real_writes_framebuffer_vm_object();
+
+    NonnullRefPtr<AnonymousVMObject> m_real_framebuffer_vmobject;
+    RefPtr<FakeWritesFramebufferVMObject> m_fake_writes_framebuffer_vmobject;
+    RefPtr<RealWritesFramebufferVMObject> m_real_writes_framebuffer_vmobject;
+    bool m_writes_are_faked { false };
+    mutable RecursiveSpinlock m_writes_state_lock;
+    CommittedPhysicalPageSet m_committed_pages;
+};
+
+}