MS contributing to Linux

[Liam Proven]

2009/7/23 Chan Chung Hang Christopher <christopher.chan at bradbury.edu.hk>:
>
>>>> And I have the same thing as Derek: the only thing that's ever crashed my
>>>> Ubuntu host is XP in VirtualBox. (It crashed it pretty hard, too, needed
>>>> more than a restart.)
>>>>
>>>>
>>>>
>>> I take it neither you nor Derek were using KVM? You running Windows with
>>> a Xen vm with paravirtualized drivers?
>>>
>>
>> As we both said - XP guest in a Linux VirtualBox host.
>>
>
> Rats, I have been using OpenSolaris for over a year but I never noticed
> Virtualbox. Guess I need to dig up a bit more on this. I take it that it
> is paravirtualization for the most part seeing that it added VMX/VT-X
> support?

If by paravirtualisation, you mean the Xen-type technique from before
hardware VT (requiring modifications to the guest OS), then no.
VirtualBox can run unmodified OSs on hardware that does not support
hardware VT.

I have not seen the level of technical detail that I would like, to be
certain, but as I understand it, both VMware and Connectix VirtualPC
for Windows use mixed native and emulated execution to get round the
limitations of virtualising x86 due to its non-compliance with the
Popek & Goldberg virtualisation requirements.

http://en.wikipedia.org/wiki/Popek_and_Goldberg_virtualization_requirements

Most x86 OSs only use Ring 3 and Ring 0; rings 1 & 2 are ignored.
VMware came up with the idea of detecting and trapping Ring 0 code and
running it through a software emulator, so that they could safely
redirect H/W accesses and safely manage the resources used by a guest
OS.

Once they'd done this, Connectix worked out how and produced a Windows
version of its existing VirtualPC product using the same method. MS
bought Connectix in 2003 to get the at-that-point-unreleased
VirtualServer product.

VirtualPC and VirtualServer are now freeware; Hyper-V is essentially
VirtualServer with the software emulation stripped out and replaced
with H/W VT. (Analogously, KVM could be considered to be QEMU with the
S/W emulation ripped & replaced with H/W VT.)

AFAIK, both VMware and VirtualPC/VirtualServer still use S/W
virtualisation. VMware reckons it's faster (q.v.
http://www.vmware.com/pdf/asplos235_adams.pdf ) and MS is not
investing much in the free products.

InnoBox's approach in VirtualBox was, I believe, rather different, and
involves coercing Ring 0 code into Ring 1, where it can be safely
managed by the hypervisor.

So, no, not exactly paravirtualisation, but /software/ virtualisation.

-- 
Liam Proven • Profile: http://www.linkedin.com/in/liamproven
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