Xf86EnableIOPorts: failed to set IOPL for I/O (Operation not permitted)

I get this error in Xorg.0.log

xf86EnableIOPorts: failed to set IOPL for I/O (Operation not permitted)

Googling quickly reveals that this error is caused by starting Xorg as non root user. Problem is that I'm running this as root.
Next possible cause SELinux, that is diabled too.

Any other possible causes of this error?

My graphicscard is

01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Thames [Radeon HD 7500M/7600M Series] (prog-if 00 [VGA controller])

But I have severe problems with the drivers, so I'm trying to run as Vesa, using this xorg.conf

Section "Device"
Identifier "Videocard0"
Driver "vesa"
EndSection