[libvirt] Question about virtio-pci in Aarch64

Thu Aug 18 12:07:39 UTC 2016

Hi Cole,
    Greate ! Thanks for your help.

On 17 August 2016 at 21:18, Cole Robinson <crobinso at redhat.com> wrote:

> On 08/17/2016 07:49 AM, Kevin Zhao wrote:
> > Hi Cole,
> >      Long time no see~
> >      Thanks for giving help me about AArch64 of virtio-pci. You have rich
> > experience about this,
> > I am green hand and seeking for your help again :-)
> >
>
> Hello again, happy to help :)
>
> > On 13 June 2016 at 06:21, Cole Robinson <crobinso at redhat.com
> > <mailto:crobinso at redhat.com>> wrote:
> >
> >     On 06/12/2016 10:29 AM, Kevin Zhao wrote:
> >     > Hi Cole && All,
> >     >      Nice meeting you in the libvirt mail-list. Greetings from
> Linaro !!!
> >     >      I am Kevin Zhao from Linaro and working for OpenStack on
> Aarch64.
> >     > Nowadays I find that the default "virtio" bus is "virtio-mmio" ,
> not
> >     > "virtio-pci". Since virtio-mmio do not has the host plugged
> function ,
> >     > something is wrong with the function in OpenStack Nova.
> >     >
> >     >       Then I search and find some mail information as belows by
> Cole :-)
> >     >       1) https://www.redhat.com/archives/libvir-list/2015-
> December/msg00217.html
> >     <https://www.redhat.com/archives/libvir-list/2015-
> December/msg00217.html>
> >     >       2) https://www.redhat.com/archives/libvir-list/2016-
> March/msg00167.html
> >     <https://www.redhat.com/archives/libvir-list/2016-
> March/msg00167.html>
> >     >
> >     >        I see some efforts have been doing by you. Really thanks
> for your
> >     > efforts for Aarch64. And I have some small questions.
> >     >       1. Is Libvirt planning to replace the default virtio-mmio to
> virtio-pci
> >     > for Aarch64?
> >
> >     We have vague plans to maybe change the virtio-mmio default to
> virtio-pci at
> >     some future point, based on some new enough qemu machine type. But
> the main
> >     blocker is that most linux distributions currently don't work out of
> the box
> >     with virtio-pci, at least Fedora doesn't as far as I know. So
> changing the
> >     default now is pre-mature
> >
> >     >       2. If not , how can I change the xml file(generated by
> Virsh) for
> >     > virtio-pci  so that Qemu can recognize it ?
> >     >
> >
> >     The latest libvirt-1.3.5 release accepts device XML containing
> <address
> >     type='pci'/> . The address block is an explicit request to libvirt to
> >     'allocate a PCI address' rather than the default virtio-mmio. So for
> example
> >     if you want to specify a virtio nic, but have it use virtio-pci
> rather than
> >     virtio-mmio, you can do something like:
> >
> >         <interface type='network'>
> >           <source network='default'/>
> >           <model type='virtio'/>
> >           <address type='pci'/>
> >         </interface>
> >
> >
> > I have changed the libvirt to 1.3.5 now, also add the pci to net-device
> xml like:
> >  <address type='pci'/>,then use the virsh to boot the VM,the total xml
> file is:
> >  https://paste.fedoraproject.org/409534/71434141/
> >
> > After booting, the eth0 device disappear(eth0 occur when the address is
> > virtio-mmio),
> > but I can find another net-device, also it can't work for dhcp:
> > 2: enp2s1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
> state
> > UP group default qlen 1000
> >     link/ether 52:54:00:0d:25:26 brd ff:ff:ff:ff:ff:ff
> >     inet6 fe80::5054:ff:fe0d:2526/64 scope link
> >        valid_lft forever preferred_lft forever
> > Running lspci:
> > 02:01.0 Ethernet controller: Red Hat, Inc Virtio network device
> >
> > My question is:
> > 1. I use Debian 8 AArch64 as the Guest OS, do you think the virtio-pci
> for
> > net-device works is OK ?
> >
>
> My guess is that the support isn't complete. Last I checked Fedora doesn't
> even work with aarch64 virtio-pci + uefi, because it requires some kernel
> changes that haven't been fully upstreamed yet. But that was several months
> ago... There may be a way to work around it nowadays but I don't personally
> know. You may want to test with either RHELSA if you have a copy, or linaro
> images.
>
You are right !  Today I happen to receive a RHEL7.3 for AArch64. I have
been
using this as Guest OS. It has virtio-pci driver.
In Libvirt 1.3.5, I use the xml :
https://paste.fedoraproject.org/410158/21672147/
Virtio-pci disk works fine(RHEL73+UEFI). But using virsh attach-device to
attach
 a device:
<disk type="file" device="disk">
      <driver name="qemu" type="qcow2"/>
      <source file="/var/lib/libvirt/images/rhel2.qcow2"/>
      <target dev="vdb" bus="virtio"/>
   <address type='pci'/>
</disk>
After adding, I can't find vdb in the Guest OS. I need to rescan the pci
by:
echo 1 > /sys/bus/pci/rescan
Then vdb appear. Do you have the same problem?

Another question, when changing to Libvirt 2.1.0, I add the : <address
type='pci'/>
to a disk device or net device, it can't work, it seems that user need to
assign
the PCI manually ?  It means that I should assign the slots and bus all by
myself?

Thanks~

>
> > 2. If I change the disk address-type to pci(Libvirt pass the virtio pci
> > parameters to Qemu for disk device), but I can't boot
> > the VM. Does Qemu not support virtio pci for  disk device in AArch64?
> >
>
> That should work fine in my testing with RHELSA, so I don't think it's a
> libvirt or qemu limitation. Probably the guest OS + UEFI.
>
> - Cole
>
> > Big Big Thanks~
> >
> >
> >     But there isn't currently any switch to say 'always give me
> virtio-pci instead
> >     of virtio-mmio'
> >
> >     - Cole
> >
> >
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/libvir-list/attachments/20160818/a3d7461d/attachment-0001.htm>