On Tue, 02 Sep 2008 18:24:52 +0100, Orchid XP v8 wrote:

>> Quote, from the wiki page you linked
>> 
>> "VMware and similar virtualization software for the x86 must employ
>> binary translation techniques to trap and virtualize the execution of
>> certain instructions. These techniques incur some performance overhead
>> as compared to a VM running on a natively virtualizable architecture"
> 
> Right. So it only emulates some instructions, instead of all of them?

Not really; at least as I understand it, if you had to emulate the 
instructions, you'd have to recompile.  What VMware and programs like it 
do is trap them and execute them within their 'sandbox'.  It's not really 
the same as emulation, which tends to be more of a translation process.

Of course, if you have a chip that supports VT (for example), then that's 
entirely different.  Or a dual-core processor/MP system, which I think 
VMware also can take advantage of, by using one core for the virtualized 
system and one for the host.  Not sure how they do that, I don't imagine 
it's well documented publicly.

I do know when I played around with virtualization a few years ago, there 
was a need to recompile kernels that were running (one of the issues that 
prevented NetWare from running natively in XEN, for example - NW kernel 
would've had to be rewritten in order to deal with the fact that it is a 
nonpreemptive OS - from what I understand from people who have worked 
closely with the NW kernel developers, that makes virtualization (at 
least as implemented in XEN 2) more difficult to achieve.

Jim

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On Mon, 01 Sep 2008 09:34:34 +0100, Invisible wrote:

> But surely if you're going to run a guest OS on the physical host CPU,
> the host CPU would need to have hardware support for enforcing the host
> seperation?

Nope.  I started running VMware back at version 2.x (now on version 6), 
hardware at that time didn't have any concept of virtualization.  The 
separation was all done in software (and very well isolated as well - 
can't think of any time where the guest took the host down when the host 
was clean).

Jim

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On Sun, 31 Aug 2008 12:48:34 -0700, Darren New wrote:

> Orchid XP v8 wrote:
>> OK, so I realise I'm probably about 20 years behind everybody else, but
>> seriously... this is THE coolest thing I've seen this year!
> 
> I've been thinking of playing with some virtual machine technology, but
> I wasn't aware there was one under Windows that would run Linux. Which
> virtual machine are you running here? (I.e., what's the Windows
> software?)

VMware has run Linux under Windows for *ages*.....

Jim

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On Mon, 01 Sep 2008 12:57:21 -0700, Darren New wrote:

> As far as I understand it, an OS running under Xen has to know it's
> running under Xen, doesn't it?

I understood that was the case under 2.0, but not sure about XEN 3.x

Jim

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Jim Henderson wrote:
> Nope.  I started running VMware back at version 2.x (now on version 6),
> hardware at that time didn't have any concept of virtualization.  The
> separation was all done in software (and very well isolated as well -
> can't think of any time where the guest took the host down when the host
> was clean).

Many security researchers intentionally run malicious and quite dangerous
software inside a VM, so it better have good isolation :)

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"Gail" <gail (at) sql in the wild (dot) co [dot] za> wrote:
> "VMware and similar virtualization software for the x86 must employ binary
> translation techniques to trap and virtualize the execution of certain
> instructions. These techniques incur some performance overhead as compared
> to a VM running on a natively virtualizable architecture"

But they're still more than acceptably fast.

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Orchid XP v8 wrote:
> 
> Wait a sec - small firm, just started up, *testing*???

Yes. Even them can do thing properly. I know one of those.. Oh, wait, I 
actually own part of it, I was building it ;).

>  From what I've seen most *large* companies don't bother to test 
> anything, never mind small startups. ;-)

Yes. Even them can do things improperly. Luckily the one I work for doesn't.

-- 
Eero "Aero" Ahonen
    http://www.zbxt.net
       aer### [at] removethiszbxtnetinvalid

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Darren New wrote:
> 
> As far as I understand it, an OS running under Xen has to know it's 
> running under Xen, doesn't it?  It's actually quite a large leap from 
> "we can run multiple OSes" to "we can run multiple OSes that don't have 
> to cooperate with the hypervisor".
> 

That's the difference, what hardware virtualization support (might be 
that also Xen 3.xx is demanded, as Jim said - dunno, 3.xx has been 
around for long enough for me to gotten started with it) does for Xen. 
Without such, the OS needs to know it's running under Xen, but if you 
have it, you can run unmodified guest OS's also.

-- 
Eero "Aero" Ahonen
    http://www.zbxt.net
       aer### [at] removethiszbxtnetinvalid

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Darren New wrote:

> As far as I understand it, an OS running under Xen has to know it's 
> running under Xen, doesn't it?

According to Wikipedia...

1. The "master" OS must be aware of Xen.

2. Originally all guest OSes had to be aware too, but Xen now supports 
running unmodified OSes as guests as well.

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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Orchid XP v8 wrote:
> 2. Originally all guest OSes had to be aware too, but Xen now supports 
> running unmodified OSes as guests as well.

You know, that's one of the things I dislike about Linux. Knowlege gets 
out of date in like 3 months. :-)

-- 
Darren New / San Diego, CA, USA (PST)

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