Re: [Qemu-devel] Help: Does Qemu support virtio-pci for net-device and disk device?

[Andrew Jones]

On Wed, Aug 17, 2016 at 06:41:33PM +0200, Andrea Bolognani wrote:
> On Wed, 2016-08-17 at 18:13 +0200, Andrew Jones wrote:
> > On Wed, Aug 17, 2016 at 08:08:11PM +0800, Kevin Zhao wrote:
> > > 
> > > Hi all,
> > >      Now I'm investigating net device hot plug and disk hotplug for
> > > AArch64. For virtio , the default address is virtio-mmio. After Libvirt
> > > 1.3.5, user can explicitly specify the address-type to pci and so libvirt
> > > will pass the virtio-pci parameters to the Qemu.
> > >      Both my host and guest OS is Debian8, and Qemu version is 2.6.0.
> > > Libvirt version is 1.3.5.
> > >      For net-device, I change the address-type to pci, and libvirt pass 
> > >the
> > > command below:
> > >      -device
> > > virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:0d:25:25,bus=pci.2,addr=0x1
> > > 
> > >      After booting, the eth0 device disappear(eth0 occur when the address
> > > is virtio-mmio),
> > > but I can find another net-device enp2s1, also it can't work for dhcp:
> > > Running lspci: 02:01.0 Ethernet controller: Red Hat, Inc Virtio network
> > > device
> > > I'm not sure whether it worked.
> > > 
> > >      For disk device,* when I change the address-type to pci, the whole
> > > qemu command is :*
> > > https://paste.fedoraproject.org/409553/,  but the VM can not boot
> > > successfully. Does Qemu not support device disk of virtio-pci in AArch64
> > > just as it in X86_64?
> > >      Thanks~Since I am not very familiar with Qemu, really looking forward
> > > to your response.
> > > 
> > > Best Regards,
> > > Kevin Zhao
> > 
> > libvirt 1.3.5 is a bit old. Later versions no longer unconditionally add
> > the i82801b11 bridge, which was necessary to use PCI devices with the PCIe
> > host bridge mach-virt has. IMO, libvirt and qemu still have a long way to
> > go in order to configure a base/standard mach-virt PCIe machine.
> 
> Debian 8, the guest OS Kevin is trying to boot, is even older,
> and in particular it doesn't have any virtio-pci support.
> 
> By the way, the same issue was raised on the libvirt list as
> well
> 
>   https://www.redhat.com/archives/libvir-list/2016-August/msg00854.html
> 
> and there's some more information there.
> 
> > 1) If we want to support both PCIe devices and PCI, then things are messy.
> >    Currently we propose dropping PCI support. mach-virt pretty much
> >    exclusively uses virtio, which can be set to PCIe mode (virtio-1.0)
> > 2) root complex ports, switches (upstream/downstream ports) are currently
> >    based on Intel parts. Marcel is thinking about creating generic models.
> 
> Huge +1 from me! Way to go, Marcel! :)
> 
> > 3) libvirt needs to learn how to plug everything together, in proper PCIe
> >    fashion, leaving holes for hotplug.
> 
> Work on this front is ongoing on the libvirt front as we speak.
> 
> > 4) Probably more... I forget all the different issues we discovered when
> >    we started playing with this a few months ago.
> > 
> > The good news is that x86 folk want all the same things for the q35 model.
> > mach-virt enthusiasts like us get to ride along pretty much for free.
> > 
> > So, using virtio-pci with mach-virt and libvirt isn't possible right now,
> > not without manual changes to the XML. It might be nice to document how to
> > manually convert a guest, so developers who want to use virtio-pci don't
> > have to abandon libvirt. I'd have to look into that, or ask one of our
> > libvirt friends to help. Certainly the instructions would be for latest
> > libvirt though.
> 
> Things are very much in flux, though, so I'm not entirely sure
> putting out any sort of official document would be a good idea
> right now. We'll definitely help eg. through the mailing lists
> and similar channels, but committing any configuration to a
> more static media seems premature.

Understood, and based on Laine's response, things are looking just
around the corner now anyway, so forget I asked :-)

> 
> > Finally, FWIW, with a guest kernel of 4.6.4-301.fc24.aarch64. The
> > following qemu command line works for me.
> > (notice the use of PCIe), and my network interface gets labeled enp0s1.
> > 
> > $QEMU -machine virt-2.6,accel=kvm -cpu host \
> >  -m 1024 -smp 1 -nographic \
> >  -bios /usr/share/AAVMF/AAVMF_CODE.fd \
> >  -device ioh3420,bus=pcie.0,id=pcie.1,port=1,chassis=1 \
> >  -device ioh3420,bus=pcie.0,id=pcie.2,port=2,chassis=2 \
> >  -device 
> >virtio-scsi-pci,disable-modern=off,disable-legacy=on,bus=pcie.1,addr=00.0,id=scsi0
> > \
> >  -drive 
> >file=/home/drjones/.local/libvirt/images/fedora.qcow2,format=qcow2,if=none,id=drive-scsi0-0-0-0
> > \
> >  -device 
> >scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1
> > \
> >  -netdev user,id=hostnet0 \
> >  -device 
> >virtio-net-pci,disable-modern=off,disable-legacy=on,bus=pcie.2,addr=00.0,netdev=hostnet0,id=net0
> > 
> > I prefer always using virtio-scsi for the disk, but a similar command
> > line can be used for a virtio-blk-pci disk.
> 
> Does the same command line work if you don't specify any of
> the disable-* options?
> 
> I'm asking because I tried running a Fedora 24 guest through
> libvirt, which doesn't support those options yet, and I get
> 
>   virtio_blk virtio2: virtio: device uses modern interface but
>                               does not have VIRTIO_F_VERSION_1
>   virtio_blk: probe of virtio2 failed with error -22

Doesn't work for me either. I can only boot with disable-modern=off,
disable-legacy=on (at least when building my config the way I try to
build it...) I presume that's a guest kernel issue.

> 
> Isn't the default for 2.6 disable-modern=off,
> disable-legacy=off? Or was that 2.7? I tried both anyway ;)

Dunno. With the command line getting longer all the time, I just
have a script that generates one that works for me, and haven't
worried much about the defaults...

Thanks,
drew