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.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();
+}
+
+}