Re: [Qemu-devel] [2.5 issue] virtio-1 in virtio-net and old vhost

[Cornelia Huck]

On Fri, 4 Dec 2015 10:06:58 +0800
Jason Wang <address@hidden> wrote:

> The problem is for pci: without this patch, guest may always see modern
> bar is "disable-modern=false". But with this patch, on an old kernel
> that does not support VERSION_1, even "disable-modern=false" were
> specified, guest can not see modern bar anymore. Looks like a guest
> visible change.

But the guest even see a modern bar if the host is not able to present
a spec-compliant device?

What we have now is a device that looks like a modern device but that
does not offer VERSION_1. Probably not spec compliant. If virtio-pci is
fixed to not present such broken devices to the guest, this is
guest-visible, yes; but only in the sense that the guest will no longer
see broken devices, but simply legacy devices if configured.