At Metztli Information Technology we hacked a circa 1995 IBM OS/2 2.11 symmetric multi-processor (SMP) system running on four(4) Intel cores. Of course, after building Oracle's VirtualBox 4.3.2 on a GNU/Linux Debian host.

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Update November 10, 2018:
Well, I briefly gave a spin to IBM OS/2 2.11 symmetric multi-processor (SMP) system on eight(8) Intel cores on VirtualBox 5.1.32

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Update April 06, 2022:
OS/2 2.1x GUI app formatting a .5 Gb virtual slice with the HPFS file system under VirtualBox 6.1.32 built from source under a Metztli Reiser4 environment:

Виктория Одинцова: Viktoriya Odintcova as Xochiquetzal, the real Mexicah's archetype of the Form of Beauty, at a mere replica of Tecpan Quetzalpapalotl : 'Palace of the Gorgeous Butterfly', located at Teotihuacan Teuhctihuacan, i.e., 'Place Where Divinities Are Created'.

(Once the video player has started, right selecting (or 'clicking') your device (or 'mouse') will show menu option, 'Open video in new tab', which will enable larger screen size.)
Update: Sometime at the begining of April, 2022, I succeeded in creating an OS/2 2.11 SMP Bootable CD ISO image  which can be installed within ten(10) minutes into a VirtualBox 6.1.32 (my build version at the time) type 2 hypervisor instance. Of course, VirtualBox is able to manipulate a 2.88 boot floppy image -- which has been 'integrated' into this OS/2 2.11 CD ISO image to make it bootable -- by adding/deleting specific drivers if/when the target is a physical SMP machine. The resulting image may then be 'burned' to physical CD media to be inserted into the CDROM device and installed into an bare metal SMP machine. The core/CPU count is at least eight(8) -- as shown in the link -- since it reflects the existing cores in my actual physical test machine.