Re: Darwin and Xen?
Re: Darwin and Xen?
- Subject: Re: Darwin and Xen?
- From: Mark Williamson <email@hidden>
- Date: Fri, 16 Feb 2007 01:53:11 +0000
> > This is the wrong answer to his question.
> >
> > Since Xen uses paravirtualization, you have to do things to the base
> > OS to make it work, that make it unable to work _without_ Xen being
> > there all the time, unless you are porting it to use Darwin as the
> > host kernel (then that's a Xen port, not a Darwin port).
There are various levels of support a guest might have for running on Xen:
1) no support at all - will (should! see below...) run in Xen under Full
Virtualisation. Can't be "domain 0" (host)
2) paravirtualised device drivers - Xen aware device drivers but OS core is
not Xen-aware. Like full virtualisation but better IO performance. Same
kernel will boot native. Can't be "domain 0" (host)
3) paravirtualised, domU support - fully Xen aware. Potentially maximal
performance, talks to Xen directly for memory management, task switching,
IO... Can't be "domain 0" (host)
4) paravirtualised, with dom0 support - fully Xen aware, plus able to manage
platform hardware. Acts as the controller for the system, builds and manages
other virtual machines, handles certain critical hardware and *usually* owns
all the PCI devices.
So, in principle, Darwin will run on Xen unmodified, but if you want it to be
your "host" environment, there's porting work to be done.
It is possible to architect a kernel that'll boot as a Xen dom0, domU or on
bare-metal hardware. Linux will be able to do this with paravirt-ops, for
instance.
> Unfortunately, your answer was a bit out of date. Xen seems to be
> dealing with vanderpool. According to the Xen FAQ
> (http://wiki.xensource.com/xenwiki/XenFaq) the can run unmodified
> Windows:
VT-x and AMD-V support have been in the tree quite a long while and work well
enough that they're used in XenSource's commercial product. I run Windows XP
under AMD-V on my home system, and have also successfully installed Syllable,
CentOS Linux and FreeBSD.
> It goes on to say that none of the BSDs work in this mode, so I
> imagine that some work on Xen would be required to get darwin
> booting. Has anybody tried it?
FreeBSD at least works in fully virtualised mode on AMD-V. NetBSD is
available as domU or dom0.
IIRC, the problem with BSDs was something really weird - like that the
bootloader uses Big Real Mode but that's not properly supported on Xen/VT-x
at the moment (whereas AMD-V provides additional hardware support for this,
so it works fine).
> What I'd like to see is support for letting an HVM guest access the
> TPM hardware, so that I could run a real, legal, software-updatable
> MacOSX in a virtual machine on a Mac, underneath Xen and
> Linux. (ducks, runs for cover..).
There are IBM folks working on TPM support.
Cheers,
Mark
--
Dave: Just a question. What use is a unicyle with no seat? And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!
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