Re: [Qemu-devel] [PATCH V2] hw/virtio-pci: fix virtio behaviour on modern (PCIe) machines

[Cornelia Huck]

On Tue, 19 Jul 2016 21:42:58 +0300
Marcel Apfelbaum <address@hidden> wrote:

> Modern machines are expected to be used by newer setups with
> modern guests aiming the use of the latest features.
> 
> Enable modern and disable legacy for virtio devices
> plugged into PCIe ports (Root ports or Downstream ports).
> Using the Virtio 1 mode will remove the limitation
> of the number of devices that can be attached to a machine
> by removing the need for the IO BAR.

Stupid question: Does this limitation show up for legacy and
transitional, but not for modern?

Would it make sense then to default to modern for PCIe and transitional
for non-PCIe?

(The term "virtio-1" mode always confuses me a bit; this may be because
ccw unlike pci does not have modern-only devices - and even if we had,
basically the only difference would be that we'd disallow devices
without the VERSION_1 feature.)