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Re: A bunch of questions about getting a working NetBSD/xen system
On Feb 2, 2010, at 6:16 PM, Louis Guillaume wrote:
> I've been struggling for a month or two now with a xen install and have a few
> general questions that I'm hoping will clear up my foggy understanding of how
> things are supposed to work:
> 0. The goal: To have a NetBSD/xen dom0 machine on which to host guest
> machines. Ideally this should:
> o run on netbsd-x-stable whatever that is at the time.
> o run unmodified oses; i.e. HVM support.
> 1. What I have:
> o Dual 3Ghz 64-bit Xeons.
> o 4G Ram.
> o Tyan S5360 Mb.
> From looking at the CPU specs it would appear that they have the
> Intel VT technology needed for HVM support.
> It does not appear that my BIOS supports this though. If I use
> "cpuctl identify" I do not see the "VT" instruction listed, and
> nowhere in my dmesg output do I have an indication that it's
> turned off in the Bios as some sources (NetBSD wiki's xen page)
> So - first question: Will it work? Or am I stuck with non-HVM and
> only modified kernels?
> Is there a way to make the system HVM-aware when the BIOS
> apparently isn't?
You say you're running a -current kernel. What version is your cpuctl command
from? And what flag are you looking for? I think it's supposed to say "vmx"
(on Intel), rather than "vt".
> 2. I've been running a -current kernel as it's been suggested that
> only -current kernels will work. But then I've seen somewhere
> that netbsd-5 should work fine.
> Can I use netbsd-5 instead of -current for DOM0/PAE yet?
Yes -- I'm doing it. But I haven't tried i386 guests or HVM guests.
> 6. What's the deal with SMP on xen? I see the following in dmesg:
> cpu0 at mainbus0 apid 0: (boot processor)
> cpu1 at mainbus0 apid 6: (application processor)
> cpu2 at mainbus0 apid 1: (application processor)
> cpu3 at mainbus0 apid 7: (application processor)
> and things like "top" only show one processor active. Last time I
> think I saw this separation of "boot" vs. "application" processor
> was in netbsd-2 or -3, I think.
> What should I expect to see here in DOM0?
The dom0 only runs on cpu0, I believe, but different guests can run on
different CPUs simultaneously. In other words, the dom0 is in some weak sense
SMP, but only weakly. That said, for many purposes -- giving separate VMs a
full CPU -- it works fine, but not for an MP guest.
I don't know what happens if you try to do, say, system builds on the DOM0 --
can it use multiple processors? I suspect not, but I'm of the minimalist DOM0
> Can I run SMP guests?
I've thought about running a Linux DOM0 and NetBSD DOMUs, but mainstream Linux
seems to be abandoning Xen, so I'd have to run a back release.
--Steve Bellovin, http://www.cs.columbia.edu/~smb
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