Wow, KVM is great :-)

[Raman Gupta]

For my Windows workloads on Linux, I've been paying VMWare for years for their
Workstation product so I can run Windows programs like Visual Studio and Quicken.
Recently, having some issues with my Windows VM (VMWare using massive amounts of memory
and CPU beyond the VM allocation, and causing random latency on my desktop), I thought the
time was finally right to try out virsh and KVM again. Converting the VMWare image to KVM
worked flawlessly via `qemu-image convert`, and then after a whole bunch of hassles
getting the right virtio drivers and guest agent installed and working, the VM is running
great. It's running flawlessly, just as fast or faster than my VMWare image, and way
more efficient on memory and CPU. And I don't need to taint my kernel to run it.

I do have some follow-up questions though:

1) It seems the networking is not quite as straightforward as VMWare for a single-VM use
case. VMWare can run the VM in bridge mode, so that it appears to the rest of my LAN as
just another PC. Host-guest, and guest-other networking works perfectly. In contrast, in
virsh, it looks like none of the 3 options are as transparent:
https://wiki.libvirt.org/page/VirtualNetworking. Running in the default NAT mode, I have
two issues:

a) My guest DNS does not transparently work to access my LAN -- only the Internet. The
docs @ https://libvirt.org/formatnetwork.html do not provide any guidance for configuring
DNS settings. I want to forward requests to the dnsmasq running on the host system.

b) What is the best way to configure my host system to be able to see the NATed IP
addresses in the virtual network?

(Fedora 27, fully updated)

Thanks!
Raman

[Raman Gupta]

>  a) My guest DNS does not transparently work to access my LAN -- only
> the Internet. The
>  docs @ https://libvirt.org/formatnetwork.html do not provide any guidance for
> configuring
>  DNS settings. I want to forward requests to the dnsmasq running on the host system.
Oops, looks like this one was easy: a <dns> element as per
https://libvirt.org/formatnetwork.html#elementsAddress.

[Tom Horsley]

On Wed, 14 Mar 2018 22:20:07 -0000
Raman Gupta wrote:

>  Running in the default NAT mode 
I always use the "bridge" networking. That way the KVM looks
like just another machine on my local network, gets an IP from
the DHCP on my router, etc. And I can delete the "default"
network and turn off all the extra junk NAT mode makes
libvirtd start (dnsmasq and such).

The one thing KVM can't do (yet anyway) is 3D accelerated
video (I occasionally look for information about the one
or two projects working on it, but the last I saw they
were still very much works in progress).

[Patrick O'Callaghan]

On Wed, 2018-03-14 at 18:51 -0400, Tom Horsley wrote:
>  On Wed, 14 Mar 2018 22:20:07 -0000
>  Raman Gupta wrote:
>  
>  > Running in the default NAT mode
>  
>  I always use the "bridge" networking. That way the KVM looks
>  like just another machine on my local network, gets an IP from
>  the DHCP on my router, etc. And I can delete the "default"
>  network and turn off all the extra junk NAT mode makes
>  libvirtd start (dnsmasq and such).
>  
>  The one thing KVM can't do (yet anyway) is 3D accelerated
>  video (I occasionally look for information about the one
>  or two projects working on it, but the last I saw they
>  were still very much works in progress). 
I do that literally every day, for Windows gaming. It took some effort
to set up but it works a treat. A good starting point is:

https://vfio.blogspot.co.uk/2015/05/vfio-gpu-how-to-series-part-1-hardwar...

Also the VFIO mailing list at https://www.redhat.com/mailman/listinfo/vfio-users

poc

[Samuel Sieb]

On 03/14/2018 04:17 PM, Patrick O'Callaghan wrote:
>  I do that literally every day, for Windows gaming. It took some
> effort
>  to set up but it works a treat. A good starting point is:
>  
>  https://vfio.blogspot.co.uk/2015/05/vfio-gpu-how-to-series-part-1-hardwar...
>  
>  Also the VFIO mailing list at https://www.redhat.com/mailman/listinfo/vfio-users 
That requires a separate video card.  There is some work on doing 
passthrough 3d which I think is supposed to be working, but only for X 
(maybe Wayland?), because there's no driver for Windows.

[Patrick O'Callaghan]

On Wed, 2018-03-14 at 16:57 -0700, Samuel Sieb wrote:
>  On 03/14/2018 04:17 PM, Patrick O'Callaghan wrote:
>  > I do that literally every day, for Windows gaming. It took some effort
>  > to set up but it works a treat. A good starting point is:
>  > 
>  > https://vfio.blogspot.co.uk/2015/05/vfio-gpu-how-to-series-part-1-hardwar...
>  > 
>  > Also the VFIO mailing list at https://www.redhat.com/mailman/listinfo/vfio-users
>  
>  That requires a separate video card.  There is some work on doing 
>  passthrough 3d which I think is supposed to be working, but only for X 
>  (maybe Wayland?), because there's no driver for Windows. 
Yes, when I said "some effort" that was what I meant, plus a fair
amount of configuration, including isolating the card from Linux so it
doesn't compete with the VM. Currently I don't see much prospect of
full 3d video passthrough given that video cards are separate
processors with (often) proprietary drivers that don't expect the video
context to change arbitrarily under their feet and don't provide a way
to snapshot their internal state (this applies to Windows too, even on
bare metal, which severely limits hibernation when using GPU drivers).
It's going to take a lot of industry effort (maybe via Vulkan, though
I'm reaching here) for this to work in the future.

poc

Open vSwitch instead of bridge (was: Re: Wow, KVM is great :-))

[Chris]

On Wed, 14 Mar 2018 18:51:00 -0400
Tom Horsley wrote:

>  On Wed, 14 Mar 2018 22:20:07 -0000
>  Raman Gupta wrote:
>  
>  > Running in the default NAT mode  
>  
>  I always use the "bridge" networking. That way the KVM looks
>  like just another machine on my local network, gets an IP from
>  the DHCP on my router, etc. And I can delete the "default"
>  network and turn off all the extra junk NAT mode makes
>  libvirtd start (dnsmasq and such). 
I also use bridge. Another solution could Open vSwitch be. It's
included since 3.x in the kernel, but haven't used it yet. Libvirt
doesn't support it I think. [1]


[1] http://docs.openvswitch.org/en/latest/howto/libvirt/

-- 
Papst Franziskus ruft zum Kampf gegen Fake News auf. Wir finden, der
Mann, der sich als Stellvertreter Christi ausgibt, von dem er
behauptet, dessen Mutter sei zeitlebens Jungfrau gewesen, er hätte über
Wasser gehen und selbiges in Wein verwandeln können, hat vollkommen
recht.

[Gordon Messmer]

On 03/14/2018 03:20 PM, Raman Gupta wrote:
>  1) It seems the networking is not quite as straightforward as VMWare
> for a single-VM use case. 

It can be.  If you want to used bridged networking, you have to create a 
bridge in Linux.  KVM doesn't handle that internally (which is to say, 
it doesn't duplicate functionality that exists in the OS).

If your existing Ethernet interface is "eth0", you could create the new 
bridge interface by running this command as root:

virsh iface-bridge eth0 br0 --no-stp