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Comment by irl_ | Hacker News Reader

There was a Microsoft Research project that made it possible to run Windows XP (or Server 2003, I don't remember exactly) as a PV guest.

That was really cool, but the whole project disappeared.

If it had been open source, I bet it would still be actively maintained to this day.

Edit: Found the paper https://www.microsoft.com/en-us/research/wp-content/uploads/...

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I will admit I've just rapidly paged through that PDF, but it looks like I'm reading a Xen introductory paper.

Xen is open source.

I found some PV IO drivers at https://wiki.xen.org/wiki/Xen_Windows_GplPv which mention XP (search for 'XP' including (!) single quotes), and a quick Google does immediately give hits on running XP as a HVM guest.

I'm (genuinely) curious what you're describing/referring to here. What project disappeared?

He's talking about Windows on Xen, which existed at a time, but was never released, like a lot of research projects. AMD-V and Intel VT made it mostly moot though.

So you mean like... NTOSKRNL et al essentially retrofitted to run in a kind of userspace?

Nice.

I don't expect that kind of thing to ever leave a research environment though. It would mess with too many people's heads and give people too many ideas of running bare-metal kernels other than NT.

Now I think about it, I realize the reason why HW virtualization really took off is because it let vendors keep their operating systems as actual operating systems in the traditional sense of the word, making for fewer legal issues (among many other reasons).

Also, I thought Xen was essentially just a super-thin layer to kickstart VT-x/AMD-V. I didn't know it could do anything else. In fact, I thought there was only emulation and hardware-assisted virtualization. Is there a middle ground I'm not aware of?

Yes. It's paravirtualization. Oh, Drawbridge is full NT in user-space, is in production now for SQL Server on Linux, but Dk (Drawbridge) is much newer. :)

TIL. That's really cool. Now I'm wondering if there are any small fully-paravirtualized hypervisors and guests I can play with. I guess Linux's support for various forms of I/O acceleration is more or less it.

I didn't know Drawbridge was that amazing - that's incredible.

And now I'm starting to understand Microsoft's vision: they have WSL to get Linux infrastructure onto Windows, and Dk to get selected Windows infrastructure onto Linux. Impressive.

But now I think about it that way, I know Dk will only ever be an internal framework - if that got released we'd basically have "perfect Wine" and it would allow quite a few too many applications to move off of NT.

WSL uses Drawbridge picoprocesses internally by the way. :)

The Drawbridge NTUM(User-Mode NT kernel) is maintained as NT 6.2 (Windows 8) which is new enough for almost all purposes - except modern Windows apps.

There's also Drawbridge...

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