diff --git a/main.h b/main.h
index 276cf78..532f54c 100644
--- a/main.h
+++ b/main.h
@@ -184,6 +184,9 @@ protected:
     bool notify(QObject* o, QEvent* e);
     static void crashHandler(int signal);
 
+protected:
+    QString m_originalSessionKey;
+
 private Q_SLOTS:
     void resetCrashesCount();
 
diff --git a/main.cpp b/main.cpp
index fa6e373..6a91e3b 100644
--- a/main.cpp
+++ b/main.cpp
@@ -42,7 +42,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <KSharedConfig>
 // Qt
 #include <qplatformdefs.h>
-#include <QDebug>
 #include <QComboBox>
 #include <qcommandlineparser.h>
 #include <QDialog>
@@ -372,7 +371,7 @@ void Application::createWorkspace()
     // critical startup section where x errors cause kwin to abort.
 
     // create workspace.
-    (void) new Workspace(isSessionRestored());
+    (void) new Workspace(m_originalSessionKey);
     emit workspaceCreated();
 }
 
diff --git a/main_x11.cpp b/main_x11.cpp
index c50aad2..b1c4a40 100644
--- a/main_x11.cpp
+++ b/main_x11.cpp
@@ -146,6 +146,11 @@ void ApplicationX11::performStartup()
         Application::setX11ScreenNumber(QX11Info::appScreen());
     }
 
+    // QSessionManager for some reason triggers a very early commitDataRequest
+    // and updates the key - before we create the workspace and load the session
+    // data -> store and pass to the workspace constructor
+    m_originalSessionKey = sessionKey();
+
     owner.reset(new KWinSelectionOwner(Application::x11ScreenNumber()));
     connect(owner.data(), &KSelectionOwner::failedToClaimOwnership, []{
         fputs(i18n("kwin: unable to claim manager selection, another wm running? (try using --replace)\n").toLocal8Bit().constData(), stderr);
@@ -291,10 +296,6 @@ KWIN_EXPORT int kdemain(int argc, char * argv[])
 
     a.start();
 
-#warning SessionManager needs porting
-#if KWIN_QT5_PORTING
-    KWin::SessionManager weAreIndeed;
-#endif
     KWin::SessionSaveDoneHelper helper;
 
     return a.exec();
diff --git a/sm.h b/sm.h
index cc63aa3..529187d 100644
--- a/sm.h
+++ b/sm.h
@@ -25,9 +25,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QDataStream>
 #include <kwinglobals.h>
 #include <QStringList>
-#if KWIN_QT5_PORTING
-#include <ksessionmanager.h>
-#endif
 #include <netwm_def.h>
 #include <QRect>
 
@@ -101,16 +98,6 @@ private:
     SmcConn conn;
 };
 
-#if KWIN_QT5_PORTING
-class SessionManager
-    : public KSessionManager
-{
-public:
-    virtual bool saveState(QSessionManager& sm);
-    virtual bool commitData(QSessionManager& sm);
-};
-#endif
-
 } // namespace
 
 #endif
diff --git a/sm.cpp b/sm.cpp
index 0e3e735..2098b7f 100644
--- a/sm.cpp
+++ b/sm.cpp
@@ -36,8 +36,26 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 namespace KWin
 {
 
-#if KWIN_QT5_PORTING
-bool SessionManager::saveState(QSessionManager& sm)
+static bool gs_sessionManagerIsKSMServer = false;
+static KConfig *sessionConfig(QString id, QString key)
+{
+    static KConfig *config = nullptr;
+    static QString lastId;
+    static QString lastKey;
+    static QString pattern = QString(QLatin1String("session/%1_%2_%3")).arg(qApp->applicationName());
+    if (id != lastId || key != lastKey) {
+        delete config;
+        config = nullptr;
+    }
+    lastId = id;
+    lastKey = key;
+    if (!config) {
+        config = new KConfig(pattern.arg(id).arg(key), KConfig::SimpleConfig);
+    }
+    return config;
+}
+
+void Workspace::saveState(QSessionManager &sm)
 {
     // If the session manager is ksmserver, save stacking
     // order, active window, active desktop etc. in phase 1,
@@ -45,37 +63,27 @@ bool SessionManager::saveState(QSessionManager& sm)
     // before the WM finishes phase 1. Saving in phase 2 is
     // too late, as possible user interaction may change some things.
     // Phase2 is still needed though (ICCCM 5.2)
-#if KWIN_QT5_PORTING
-    char* sm_vendor = SmcVendor(static_cast< SmcConn >(sm.handle()));
-    bool ksmserver = qstrcmp(sm_vendor, "KDE") == 0;
-    free(sm_vendor);
-#else
-#warning need to figure out whether the used SessionManager is ksmserver
-    bool ksmserver = false;
-#endif
+    KConfig *config = sessionConfig(sm.sessionId(), sm.sessionKey());
     if (!sm.isPhase2()) {
-        Workspace::self()->sessionSaveStarted();
-        if (ksmserver)   // save stacking order etc. before "save file?" etc. dialogs change it
-            Workspace::self()->storeSession(kapp->sessionConfig(), SMSavePhase0);
+        KConfigGroup cg(config, "Session");
+        cg.writeEntry("AllowsInteraction", sm.allowsInteraction());
+        sessionSaveStarted();
+        if (gs_sessionManagerIsKSMServer)   // save stacking order etc. before "save file?" etc. dialogs change it
+            storeSession(config, SMSavePhase0);
         sm.release(); // Qt doesn't automatically release in this case (bug?)
         sm.requestPhase2();
-        return true;
+        return;
     }
-    Workspace::self()->storeSession(kapp->sessionConfig(), ksmserver ? SMSavePhase2 : SMSavePhase2Full);
-#if KWIN_QT5_PORTING
-    kapp->sessionConfig()->sync();
-#endif
-    return true;
+    storeSession(config, gs_sessionManagerIsKSMServer ? SMSavePhase2 : SMSavePhase2Full);
+    config->sync();
 }
 
 // I bet this is broken, just like everywhere else in KDE
-bool SessionManager::commitData(QSessionManager& sm)
+void Workspace::commitData(QSessionManager &sm)
 {
     if (!sm.isPhase2())
-        Workspace::self()->sessionSaveStarted();
-    return true;
+        sessionSaveStarted();
 }
-#endif
 
 // Workspace
 
@@ -194,18 +202,18 @@ void Workspace::storeSubSession(const QString &name, QSet<QByteArray> sessionIds
 
   \sa storeSession()
  */
-void Workspace::loadSessionInfo()
+void Workspace::loadSessionInfo(const QString &key)
 {
+    // NOTICE: qApp->sessionKey() is outdated when this gets invoked
+    // the key parameter is cached from the application constructor.
     session.clear();
-#if KWIN_QT5_PORTING
-    KConfigGroup cg(kapp->sessionConfig(), "Session");
-
+    KConfigGroup cg(sessionConfig(qApp->sessionId(), key), "Session");
     addSessionInfo(cg);
-#endif
 }
 
 void Workspace::addSessionInfo(KConfigGroup &cg)
 {
+    m_initialDesktop = cg.readEntry(QStringLiteral("desktop"), 1);
     int count =  cg.readEntry("count", 0);
     int active_client = cg.readEntry("active", 0);
     for (int i = 1; i <= count; i++) {
@@ -408,9 +416,8 @@ static void shutdown_cancelled(SmcConn conn_P, SmPointer ptr)
 
 void SessionSaveDoneHelper::saveDone()
 {
-#if KWIN_QT5_PORTING
-    Workspace::self()->sessionSaveDone();
-#endif
+    if (Workspace::self())
+        Workspace::self()->sessionSaveDone();
 }
 
 SessionSaveDoneHelper::SessionSaveDoneHelper()
@@ -433,6 +440,15 @@ SessionSaveDoneHelper::SessionSaveDoneHelper()
         free(id);
     if (conn == NULL)
         return; // no SM
+
+    // detect ksmserver
+    // NOTICE: no idea whether the assumptions about it in Workspace::saveState()
+    // still hold for KF5/Plasma 5
+#warning assuming special behavior in ksmserver to be still present in KF5
+    char* vendor = SmcVendor(conn);
+    gs_sessionManagerIsKSMServer = qstrcmp(vendor, "KDE") == 0;
+    free(vendor);
+
     // set the required properties, mostly dummy values
     SmPropValue propvalue[ 5 ];
     SmProp props[ 5 ];
diff --git a/workspace.h b/workspace.h
index 4acefb4..84d6edf 100644
--- a/workspace.h
+++ b/workspace.h
@@ -62,7 +62,7 @@ class KWIN_EXPORT Workspace : public QObject
 {
     Q_OBJECT
 public:
-    explicit Workspace(bool restore = false);
+    explicit Workspace(const QString &sessionKey = QString());
     virtual ~Workspace();
 
     static Workspace* self() {
@@ -431,6 +431,10 @@ private Q_SLOTS:
     void slotDesktopCountChanged(uint previousCount, uint newCount);
     void slotCurrentDesktopChanged(uint oldDesktop, uint newDesktop);
 
+    // session management
+    void saveState(QSessionManager &sm);
+    void commitData(QSessionManager &sm);
+
 Q_SIGNALS:
     /**
      * Emitted after the Workspace has setup the complete initialization process.
@@ -503,7 +507,8 @@ private:
     QWidget* active_popup;
     Client* active_popup_client;
 
-    void loadSessionInfo();
+    int m_initialDesktop;
+    void loadSessionInfo(const QString &key);
     void addSessionInfo(KConfigGroup &cg);
 
     QList<SessionInfo*> session;
diff --git a/workspace.cpp b/workspace.cpp
index 09ae9a2..9e71494 100644
--- a/workspace.cpp
+++ b/workspace.cpp
@@ -99,12 +99,13 @@ void ColorMapper::update()
 
 Workspace* Workspace::_self = 0;
 
-Workspace::Workspace(bool restore)
+Workspace::Workspace(const QString &sessionKey)
     : QObject(0)
     , m_compositor(NULL)
     // Unsorted
     , active_popup(NULL)
     , active_popup_client(NULL)
+    , m_initialDesktop(1)
     , active_client(0)
     , last_active_client(0)
     , most_recently_raised(0)
@@ -155,8 +156,10 @@ Workspace::Workspace(bool restore)
 
     delayFocusTimer = 0;
 
-    if (restore)
-        loadSessionInfo();
+    if (!sessionKey.isEmpty())
+        loadSessionInfo(sessionKey);
+    connect(qApp, SIGNAL(commitDataRequest(QSessionManager&)), SLOT(commitData(QSessionManager&)));
+    connect(qApp, SIGNAL(saveStateRequest(QSessionManager&)), SLOT(saveState(QSessionManager&)));
 
     RuleBook::create(this)->load();
 
@@ -260,18 +263,9 @@ void Workspace::init()
 
     // Extra NETRootInfo instance in Client mode is needed to get the values of the properties
     NETRootInfo client_info(connection(), NET::ActiveWindow | NET::CurrentDesktop);
-    int initial_desktop;
     if (!qApp->isSessionRestored())
-        initial_desktop = client_info.currentDesktop();
-    else {
-#if KWIN_QT5_PORTING
-        KConfigGroup group(kapp->sessionConfig(), "Session");
-        initial_desktop = group.readEntry("desktop", 1);
-#else
-        initial_desktop = 1;
-#endif
-    }
-    if (!VirtualDesktopManager::self()->setCurrent(initial_desktop))
+        m_initialDesktop = client_info.currentDesktop();
+    if (!VirtualDesktopManager::self()->setCurrent(m_initialDesktop))
         VirtualDesktopManager::self()->setCurrent(1);
 
     reconfigureTimer.setSingleShot(true);