On Fri, Dec 04, 2015 at 11:15:48AM +0100, Cornelia Huck wrote: > On Fri, 4 Dec 2015 10:06:58 +0800 > Jason Wang <jasow...@redhat.com> 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.
I agree - we don't have to keep what's broken, broken. If guests are known not to work, we don't worry about how well they migrate. -- MST
