VMware working on Xen virtual machines importing capability?

While deep diving in Workstation 6 configurations options for improving new technical tip How to run ESX Server 3 on a VMware Workstation 6 virtual machine, I discovered a new undocumented option, exposed by virtualization hacker Ulli Hankeln:

  • hypervisor.xen.allow (which can be set as = “TRUE”)

Presence of this setting may imply VMware is working on importing capabilities for Xen-based virtual machines, now that Workstation 6 includes (experimental) support for para-virtualized Linux guest OS.

Check complete list of advanced entries for VMware configurations files (.vmx) at source.

Update: a VMware developer commented this post and provided detailed explaination for the feature.

Normally, booting VMware within a Xen kernel causes workstation to freeze solid – Xen mis-emulates the VMware backdoor instruction (real hardware causes a processor exception; Xen enters an infinite loop on the instruction). WS6 code now checks for the presence of a Xen hypervisor, and refuses to start a virtual machine if one is detected. “hypervisor.xen.allow” disables this check.

The option is present so that Xen developers could (if they desire) disable the check, thus allowing a VMware virtual machine to run in a Xen guest as far as bugs permit. I would hope that eventually Xen becomes robust enough to run a full VMware virtual machine within a guest, and when such a day arrives “hypervisor.xen.allow” can retire. Until then, a helpful error message is better than an obscure hang.