bug#22633: Provide a kvm-less qemu / guix system vm

[Leo Famulari <leo@famulari.name>]

On Fri, Feb 12, 2016 at 10:04:47AM -0800, Christopher Allan Webber wrote:
> Leo Famulari writes:
> 
> > On Fri, Feb 12, 2016 at 09:50:09AM +1100, Jookia wrote:
> >> On Thu, Feb 11, 2016 at 09:26:12AM -0800, Christopher Allan Webber wrote:
> >> > So on my Libreboot-enabled machine, KVM does not work.  In fact, even
> >> > starting qemu with KVM enabled on it appears to crash my whole system.
> >> > Not only does "guix system vm" not work, even "guix system vm-image" can
> >> > take the whole machine down!
> >> 
> >> Currently the 'solution' I've found is to edit Guix to remove the two instances
> >> of '--enable-kvm' which works somewhat, though it's slower as there's absolutely
> >> no acceleration.
> >> 
> >> > It would be nice to have a --no-kvm switch, because I'd really like to
> >> > make use of Guix's nice VM features!
> >
> > It's not a proper fix, but this patch achieves that on my non-Libreboot
> > machine. Can you see if it works for you?
> >
> > [...]
> 
> Good news there, that does work and I am able to boot a VM through that
> route!
> 
> I would really like to be able to protect myself from accidentally
> crashing my system by making sure that if /dev/kvm is not there that we
> don't do --enable-kvm, so maybe I could do that if we can figure out how
> to make blacklisting actually work.  In the meanwhile, maybe I should
> add a --no-kvm flag to "guix system vm"?

We definitely want to automatically disable KVM if it's not available.
But I think it would also be useful to have a --no-kvm option.