kvm, xen and what requires H/W virt support?

[Robert P. J. Day]

i might have asked this once and forgotten the answer but here:

http://fedoraproject.org/wiki/Docs/Beats/Virtualization

the caution near the bottom:

"KVM requires hardware virtualization features in the host system.
Systems lacking hardware virtualization do not support Xen guests at
this time."

i'm confused since this seems to be mixing two issues -- what basic
KVM requires, as opposed to which systems support Xen guests.  would
there be a clearer way to word that?

rday
--

========================================================================
Robert P. J. Day                               Waterloo, Ontario, CANADA

Linux Consulting, Training and Kernel Pedantry.

Web page:                                          http://crashcourse.ca
Twitter:                                       http://twitter.com/rpjday
========================================================================

[John Poelstra]

Robert P. J. Day said the following on 02/01/2010 02:23 PM Pacific Time:
> i might have asked this once and forgotten the answer but here:
>
> http://fedoraproject.org/wiki/Docs/Beats/Virtualization
>
> the caution near the bottom:
>
> "KVM requires hardware virtualization features in the host system.
> Systems lacking hardware virtualization do not support Xen guests at
> this time."

"System" is ambiguous?

How about: "KVM requires hardware virtualization features in the host 
system's CPU."

John

[Justin Forbes]

On Mon, Feb 01, 2010 at 05:23:48PM -0500, Robert P. J. Day wrote:
> i might have asked this once and forgotten the answer but here:
>
> http://fedoraproject.org/wiki/Docs/Beats/Virtualization
>
> the caution near the bottom:
>
> "KVM requires hardware virtualization features in the host system.
> Systems lacking hardware virtualization do not support Xen guests at
> this time."
>
> i'm confused since this seems to be mixing two issues -- what basic
> KVM requires, as opposed to which systems support Xen guests.  would
> there be a clearer way to word that?

Well, I am not sure where this is coming from at all.  Technically speaking
F-12 doesn't support any xen guests, as we have no dom0, though it will
happily run *as* a xen guest in either paravirt or fullvirt.
Perhaps the intention was to point out that systems without hardare virt
capabilities cannot run xen either, since we don't ship a dom0?

Justin

[Robert P. J. Day]

On Tue, 2 Feb 2010, Justin M. Forbes wrote:
> On Mon, Feb 01, 2010 at 05:23:48PM -0500, Robert P. J. Day wrote:
> > i might have asked this once and forgotten the answer but here:
> >
> > http://fedoraproject.org/wiki/Docs/Beats/Virtualization
> >
> > the caution near the bottom:
> >
> > "KVM requires hardware virtualization features in the host system.
> > Systems lacking hardware virtualization do not support Xen guests
> > at this time."
> >
> > i'm confused since this seems to be mixing two issues -- what
> > basic KVM requires, as opposed to which systems support Xen
> > guests.  would there be a clearer way to word that?
>
> Well, I am not sure where this is coming from at all.  Technically
> speaking F-12 doesn't support any xen guests, as we have no dom0,
> though it will happily run *as* a xen guest in either paravirt or
> fullvirt. Perhaps the intention was to point out that systems
> without hardare virt capabilities cannot run xen either, since we
> don't ship a dom0?

not sure where *what* is coming from?  the note in question, or my
apparent confusion? :-)

maybe i phrased it badly.  if i were to read just the first sentence
of that note:

"KVM requires hardware virtualization features in the host system."

then, IMHO, the obvious logical consequence of that (redundantly)
would be to say,

"Therefore, if your system does not have H/W virt support, you simply
cannot run KVM."

but after i read that first sentence (which made perfect sense), i
have no idea how that logically leads into that subsequent sentence:

"Systems lacking hardware virtualization do not support Xen guests
at this time."

regardless of the truth of that claim, it just doesn't seem to
follow from the first sentence.  in short, what's it doing there?  how
are those two points related?  what does that have to do with KVM?  or
am i just being dense?

rday
--

========================================================================
Robert P. J. Day                               Waterloo, Ontario, CANADA

Linux Consulting, Training and Kernel Pedantry.

Web page:                                          http://crashcourse.ca
Twitter:                                       http://twitter.com/rpjday
========================================================================

[Bill McGonigle]

On 02/02/2010 09:08 AM, Robert P. J. Day wrote:
> regardless of the truth of that claim, it just doesn't seem to
> follow from the first sentence.  in short, what's it doing there?  how
> are those two points related?  what does that have to do with KVM?  or
> am i just being dense?

I think what this is trying to get at is running Xen DomU's under KVM 
using Xenner, which is just another way to invoke KVM so it needs 
hardware virt assist.

Somebody might be upgrading a machine, and that machine may lack 
hardware virt assist because it's been a Xen Dom0 and Xen can do PV just 
fine without hardware assist.

So, if somebody upgrades to Fedora 12 from Fedora 8 they'll be SOL if 
they were running a Xen system, unless they have hw virt, in which case 
they'll be OK with KVM and Xenner (or if they install the experimental 
Dom0 support).

-Bill

[Boris Derzhavets]

> Well, I am not sure where this is coming from at all.  Technically speaking
> F-12 doesn't support any xen guests, as we have no dom0, though it will
> happily run *as* a xen guest in either paravirt or fullvirt.
> Perhaps the intention was to point out that systems without hardare virt
> capabilities cannot run xen either, since we don't ship a dom0?

What for xen-3.4.2-2.fc13.src.rpm has been written ?

--- On Tue, 2/2/10, Justin M. Forbes  wrote:

From: Justin M. Forbes 
Subject: Re: [fedora-virt] kvm, xen and what requires H/W virt support?
To: "Robert P. J. Day" 
Cc: "Fedora Virtualization Mailing List" 
Date: Tuesday, February 2, 2010, 8:57 AM

On Mon, Feb 01, 2010 at 05:23:48PM -0500, Robert P. J. Day wrote:
> i might have asked this once and forgotten the answer but here:
>
> http://fedoraproject.org/wiki/Docs/Beats/Virtualization
>
> the caution near the bottom:
>
> "KVM requires hardware virtualization features in the host system.
> Systems lacking hardware virtualization do not support Xen guests at
> this time."
>
> i'm confused since this seems to be mixing two issues -- what basic
> KVM requires, as opposed to which systems support Xen guests.  would
> there be a clearer way to word that?

Well, I am not sure where this is coming from at all.  Technically speaking
F-12 doesn't support any xen guests, as we have no dom0, though it will
happily run *as* a xen guest in either paravirt or fullvirt.
Perhaps the intention was to point out that systems without hardare virt
capabilities cannot run xen either, since we don't ship a dom0?

Justin
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