4 times higher CPU usage compared to Qt 4 due to insufficient SHM permissions

Applications like Qt Designer have 4-10 times higher CPU usage compared to Qt 4.8 with native backend.

most of time is spent in following function according to callgrind
1,626,605,760 ???:xcb_image_put_pixel [/usr/lib64/libxcb-image.so.0.0.0]
1,599,495,664 ???:xcb_image_get_pixel [/usr/lib64/libxcb-image.so.0.0.0]
406,999,190 ???:xcb_image_subimage [/usr/lib64/libxcb-image.so.0.0.0]

which are probably called from QXcbShmImage::put

probably relevant information:
following code returns error when my Qt application is running:

if (shm_present)
error = xcb_request_check(xcb_connection(), xcb_shm_attach_checked(xcb_connection(), m_shm_info.shmseg, m_shm_info.shmid, false));

(gdb) print *error
$4 = {response_type = 0 '\000', error_code = 10 '\n', sequence = 464, resource_id = 14729351, minor_code = 1, major_code = 130 '\202', pad0 = 0 '\000', pad =

, full_sequence = 464}
(gdb) bt
#0 QXcbShmImage::QXcbShmImage (this=0x2aaaaf1bc70, screen=<optimized out>, size=..., depth=<optimized out>, format=QImage::Format_ARGB32_Premultiplied) at qxcbbackingstore.cpp:125
#1 0x000003fff293555a in QXcbBackingStore::resize (this=0x2aaaaf21c30, size=...) at qxcbbackingstore.cpp:371
#2 0x000003fff77deb80 in QWidgetBackingStore::doSync() () from /usr/lib64/libQt5Widgets.so.5
#3 0x000003fff77e0094 in QWidgetBackingStore::sync(QWidget*, QRegion const&) () from /usr/lib64/libQt5Widgets.so.5
#4 0x000003fff783f9bb in QWidgetWindow::event(QEvent*) () from /usr/lib64/libQt5Widgets.so.5
#5 0x000003fff77d036c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib64/libQt5Widgets.so.5
#6 0x000003fff77d601a in QApplication::notify(QObject*, QEvent*) () from /usr/lib64/libQt5Widgets.so.5
#7 0x000003fff6e8607d in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib64/libQt5Core.so.5
#8 0x000003fff725b3e8 in sendSpontaneousEvent (event=0x3ffffffb700, receiver=0x2aaaaf1c560) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:231
#9 QGuiApplicationPrivate::processExposeEvent (e=0x2aaaae55eb0) at kernel/qguiapplication.cpp:2610
#10 0x000003fff725c1bd in QGuiApplicationPrivate::processWindowSystemEvent (e=e@entry=0x2aaaae55eb0) at kernel/qguiapplication.cpp:1635
#11 0x000003fff723a8f9 in QWindowSystemInterface::sendWindowSystemEvents (flags=..., flags@entry=...) at kernel/qwindowsysteminterface.cpp:572
#12 0x000003fff2958b9a in QUnixEventDispatcherQPA::processEvents (this=<optimized out>, flags=...) at eventdispatchers/qunixeventdispatcher.cpp:63
#13 0x000003fff6e83cd3 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/libQt5Core.so.5
#14 0x000003fff6e8ba8a in QCoreApplication::exec() () from /usr/lib64/libQt5Core.so.5
#15 0x000002aaaaac661e in main (piarg=1, Pcarg=<optimized out>) at main.cpp:6435