virtualbox.org

Hello, I recently downloaded Virtual Box to try it out on a Xen VPS that I have but am unable to get it running. After some pain getting Virtual Box installed, it keeps getting killed when I try to start a VM. When I check dmesg this is what I see every time it's killed:

swap_dup: Bad swap file entry 30000020
VM: killing process VBoxHeadless
swap_free: Bad swap file entry 30000020

I don't think I'm running out of memory, as I have most of 512 MBs RAM free and 1.5 GBs of swap, and this happens even when I restrict the VM to 64 MBs of memory. After googling, I've seen some indication that this might be because the vboxdrv kernel module has some memory bug that is corrupting a pagefile. If anyone has any idea on this, please let me know.

VirtualBox can't run in a Xen dom0. The two products are not compatible.

It's actually a DomU kernel, sorry, I thought I mentioned that before. I think I've seen people mention that they got virtualbox running on a Xen VPS before. Are you sure it won't work?

Maybe it will work on an HVM DomU.

Isn't the whole point of Xen that the DomU kernels include Xen aware drivers so that they can indirectly invoke Dom0 services? How is a DomU machine going to work untethered in VBox which doesn't provide these. I've searched this forum and there isn't a relevant hit on DomU.

TerryE, you did not read the previous posts in this thread carefully and misunderstood what we're talking about. I have a Xen VPS running a DomU kernel and want to run virtual box on top of that, so I can run FreeBSD or Solaris and not the crap linux that comes with the VPS. You're talking about running a Xen DomU kernel on top of Virtual Box, which nobody else is talking about.

You are right. I missed that point.

At the nub of this, we still have the impasse that lies at the heart of all VM systems. It is one that we try to ignore at our peril whether we describe this in shades of "The Matrix" or we discuss it in Popek and Goldberg terms. A virtualisation environment has to enable the guest OS and system to run as if it were in control of its own environment, and there are three broad strategies for doing this:

1. The H/W itself enables P&G virtualisation; and both Intel and AMD have recently introduced such support with their VT-x and AND-V architectures.
2. The VM S/W carries some form of JiT code translation of the guest (read Keith Adams excellent paper A Comparison of Software and Hardware Techniques for x86 Virtualization for a detailed description of how this works.)
3. The guest OS actively cooperates in "the lie" and is host VM aware.

In practice most modern VM products are hybrids of these. Classic Xen was architected as category 3; classic VBox and VMware were category 2, though in reality they are both category 3 hybrids (the VMware tools and VBox guest additions are just guest aware drivers that bypass the major overheads of IO and privileged instruction virtualisation by calling the VM host directly).

Category 2 and 3 systems just do not nest well. At worst the assumptions which underpin the abstraction model fail, and something panics/BSODs either in the guest or host OS; at best the result runs like a total dog. So you are forced to introduce category 1 into the mix. Xen, WMvare and VBox now include HW virtualisation support and are continuing to develop this. With the second generation HW implementations, these are now starting to outperform pure category 2 systems. However again running HW virtualisation in the guest OS usually defeats the Host VM system.

Given that your Host is a Xen micro-kernel, you are left with the option of running H/W assist within Xen, indeed Xen will now run BSD and OpenSolaris as a guest under its H/W assist variant. Forget trying to run VBox in a DomU environment until someone like Sander says “This is now a supported host environment”. “Maybe it will work” is just too fluffy.

Thanks for the writeup, Terry, and the info, Sander. Looks like I'm out of luck for now but at least the Virtual Box kernel module compiled: I couldn't even get the VMware kernel module to compile for the domU kernel.