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.

5 files changed, 219 insertions, 2 deletions

diff --git a/Kernel/CMakeLists.txt b/Kernel/CMakeLists.txt
index 2e52cea77c..2e4bfe317c 100644
--- a/Kernel/CMakeLists.txt
+++ b/Kernel/CMakeLists.txt
@@ -181,6 +181,7 @@ set(KERNEL_SOURCES
     Memory/RingBuffer.cpp
     Memory/ScatterGatherList.cpp
     Memory/ScopedAddressSpaceSwitcher.cpp
+    Memory/SharedFramebufferVMObject.cpp
     Memory/SharedInodeVMObject.cpp
     Memory/VMObject.cpp
     Memory/VirtualRange.cpp
diff --git a/Kernel/Forward.h b/Kernel/Forward.h
index 7fcedb1d2a..667fd605bf 100644
--- a/Kernel/Forward.h
+++ b/Kernel/Forward.h
@@ -25,6 +25,7 @@ class DiskCache;
 class DoubleBuffer;
 class File;
 class OpenFileDescription;
+class DisplayConnector;
 class FileSystem;
 class FutexQueue;
 class IPv4Socket;
diff --git a/Kernel/Memory/SharedFramebufferVMObject.cpp b/Kernel/Memory/SharedFramebufferVMObject.cpp
new file mode 100644
index 0000000000..f0ea27e874
--- /dev/null
+++ b/Kernel/Memory/SharedFramebufferVMObject.cpp
@@ -0,0 +1,120 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/FileSystem/Inode.h>
+#include <Kernel/Locking/Spinlock.h>
+#include <Kernel/Memory/SharedFramebufferVMObject.h>
+
+namespace Kernel::Memory {
+
+ErrorOr<NonnullRefPtr<SharedFramebufferVMObject>> SharedFramebufferVMObject::try_create_for_physical_range(PhysicalAddress paddr, size_t size)
+{
+    auto real_framebuffer_vmobject = TRY(AnonymousVMObject::try_create_for_physical_range(paddr, size));
+    auto new_physical_pages = TRY(VMObject::try_create_physical_pages(size));
+    auto committed_pages = TRY(MM.commit_user_physical_pages(ceil_div(size, static_cast<size_t>(PAGE_SIZE))));
+    auto vm_object = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) SharedFramebufferVMObject(move(new_physical_pages), move(committed_pages), real_framebuffer_vmobject)));
+    TRY(vm_object->create_fake_writes_framebuffer_vm_object());
+    TRY(vm_object->create_real_writes_framebuffer_vm_object());
+    return vm_object;
+}
+
+ErrorOr<NonnullRefPtr<SharedFramebufferVMObject>> SharedFramebufferVMObject::try_create_at_arbitrary_physical_range(size_t size)
+{
+    auto real_framebuffer_vmobject = TRY(AnonymousVMObject::try_create_with_size(size, AllocationStrategy::AllocateNow));
+    auto new_physical_pages = TRY(VMObject::try_create_physical_pages(size));
+    auto committed_pages = TRY(MM.commit_user_physical_pages(ceil_div(size, static_cast<size_t>(PAGE_SIZE))));
+    auto vm_object = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) SharedFramebufferVMObject(move(new_physical_pages), move(committed_pages), real_framebuffer_vmobject)));
+    TRY(vm_object->create_fake_writes_framebuffer_vm_object());
+    TRY(vm_object->create_real_writes_framebuffer_vm_object());
+    return vm_object;
+}
+
+ErrorOr<NonnullRefPtr<SharedFramebufferVMObject::FakeWritesFramebufferVMObject>> SharedFramebufferVMObject::FakeWritesFramebufferVMObject::try_create(Badge<SharedFramebufferVMObject>, SharedFramebufferVMObject const& parent_object)
+{
+    auto new_physical_pages = TRY(VMObject::try_create_physical_pages(0));
+    return adopt_nonnull_ref_or_enomem(new (nothrow) FakeWritesFramebufferVMObject(parent_object, move(new_physical_pages)));
+}
+
+ErrorOr<NonnullRefPtr<SharedFramebufferVMObject::RealWritesFramebufferVMObject>> SharedFramebufferVMObject::RealWritesFramebufferVMObject::try_create(Badge<SharedFramebufferVMObject>, SharedFramebufferVMObject const& parent_object)
+{
+    auto new_physical_pages = TRY(VMObject::try_create_physical_pages(0));
+    return adopt_nonnull_ref_or_enomem(new (nothrow) RealWritesFramebufferVMObject(parent_object, move(new_physical_pages)));
+}
+
+ErrorOr<void> SharedFramebufferVMObject::create_fake_writes_framebuffer_vm_object()
+{
+    m_fake_writes_framebuffer_vmobject = TRY(FakeWritesFramebufferVMObject::try_create({}, *this));
+    return {};
+}
+
+ErrorOr<void> SharedFramebufferVMObject::create_real_writes_framebuffer_vm_object()
+{
+    m_real_writes_framebuffer_vmobject = TRY(RealWritesFramebufferVMObject::try_create({}, *this));
+    return {};
+}
+
+Span<RefPtr<PhysicalPage>> SharedFramebufferVMObject::real_framebuffer_physical_pages()
+{
+    return m_real_framebuffer_vmobject->physical_pages();
+}
+Span<RefPtr<PhysicalPage> const> SharedFramebufferVMObject::real_framebuffer_physical_pages() const
+{
+    return m_real_framebuffer_vmobject->physical_pages();
+}
+
+Span<RefPtr<PhysicalPage>> SharedFramebufferVMObject::fake_sink_framebuffer_physical_pages()
+{
+    return m_physical_pages.span();
+}
+
+Span<RefPtr<PhysicalPage> const> SharedFramebufferVMObject::fake_sink_framebuffer_physical_pages() const
+{
+    return m_physical_pages.span();
+}
+
+void SharedFramebufferVMObject::switch_to_fake_sink_framebuffer_writes(Badge<Kernel::DisplayConnector>)
+{
+    SpinlockLocker locker(m_writes_state_lock);
+    m_writes_are_faked = true;
+    for_each_region([](Region& region) {
+        region.remap();
+    });
+}
+void SharedFramebufferVMObject::switch_to_real_framebuffer_writes(Badge<Kernel::DisplayConnector>)
+{
+    SpinlockLocker locker(m_writes_state_lock);
+    m_writes_are_faked = false;
+    for_each_region([](Region& region) {
+        region.remap();
+    });
+}
+
+Span<RefPtr<PhysicalPage> const> SharedFramebufferVMObject::physical_pages() const
+{
+    SpinlockLocker locker(m_writes_state_lock);
+    if (m_writes_are_faked)
+        return VMObject::physical_pages();
+    return m_real_framebuffer_vmobject->physical_pages();
+}
+Span<RefPtr<PhysicalPage>> SharedFramebufferVMObject::physical_pages()
+{
+    SpinlockLocker locker(m_writes_state_lock);
+    if (m_writes_are_faked)
+        return VMObject::physical_pages();
+    return m_real_framebuffer_vmobject->physical_pages();
+}
+
+SharedFramebufferVMObject::SharedFramebufferVMObject(FixedArray<RefPtr<PhysicalPage>>&& new_physical_pages, CommittedPhysicalPageSet committed_pages, AnonymousVMObject& real_framebuffer_vmobject)
+    : VMObject(move(new_physical_pages))
+    , m_real_framebuffer_vmobject(real_framebuffer_vmobject)
+    , m_committed_pages(move(committed_pages))
+{
+    // Allocate all pages right now. We know we can get all because we committed the amount needed
+    for (size_t i = 0; i < page_count(); ++i)
+        m_physical_pages[i] = m_committed_pages.take_one();
+}
+
+}
diff --git a/Kernel/Memory/SharedFramebufferVMObject.h b/Kernel/Memory/SharedFramebufferVMObject.h
new file mode 100644
index 0000000000..90e195aa34
--- /dev/null
+++ b/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;
+};
+
+}
diff --git a/Kernel/Memory/VMObject.h b/Kernel/Memory/VMObject.h
index 24898722a8..7432181ecf 100644
--- a/Kernel/Memory/VMObject.h
+++ b/Kernel/Memory/VMObject.h
@@ -34,8 +34,9 @@ public:
     virtual bool is_private_inode() const { return false; }
 
     size_t page_count() const { return m_physical_pages.size(); }
-    Span<RefPtr<PhysicalPage> const> physical_pages() const { return m_physical_pages.span(); }
-    Span<RefPtr<PhysicalPage>> physical_pages() { return m_physical_pages.span(); }
+
+    virtual Span<RefPtr<PhysicalPage> const> physical_pages() const { return m_physical_pages.span(); }
+    virtual Span<RefPtr<PhysicalPage>> physical_pages() { return m_physical_pages.span(); }
 
     size_t size() const { return m_physical_pages.size() * PAGE_SIZE; }