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

[Laine Stump]

On 08/19/2016 11:43 AM, Andrea Bolognani wrote:
> On Thu, 2016-08-18 at 08:38 +0200, Andrew Jones wrote:
> > > > 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.
> I tried Fedora 24 and Debian testing, and for both of them
> the result is the same: I can only boot the guest if I'm
> setting up a legacy-free PCIe topology and use virt-2.7 to
> obtain virtio-1.0 devices (see below); for every other
> permutation of
>
>    { PCI topology, PCIe topology } x { virt-2.6, virt-2.7 }
>
> the guest doesn't boot at all.
>
> On the other hand, a RHEL 7.3 guest was able to boot *every
> single time*, even though the result was in some cases
> quite questionable (eg. legacy PCI devices plugged into
> ioh3420 ports).
>
> > > 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...
> So I thought the default for 2.6 was supposed to be
>
>    disable-modern=off,disable-legacy=off  [0.9+1.0]
>
> but it turns out it's actually
>
>    disable-modern=on,disable-legacy=off       [0.9]

Huh. I had thought it switched to disable-modern=off with 2.6 as well.

> whereas the default for 2.7 is
>
>    disable-modern=off,disable-legacy=on       [1.0]
>
> Is the idea that there would be a QEMU release with both
> 0.9 and 1.0 enabled by default something that I just
> imagined? Or did the plan just change at some point?

If I understand the patches correctly, the default for 2.7 will be 
different depending on the type of slot:

pcie-root -> disable-modern=off,disable-legacy=off
legacy PCI -> disable-modern=off,disable-legacy=off
pcie-*-port -> disable-modern=off,disable-legacy=on

The idea is to eliminate the need for the pcie-*-port to reserve IO port 
space (this isn't an issue on pcie-root, so the default is different).