On Mon, 4 Feb 2019 23:45:35 +0100 David Hildenbrand <da...@redhat.com> wrote:
> On 04.02.19 23:42, Collin Walling wrote: > > On 2/4/19 4:54 PM, David Hildenbrand wrote: > >> On 04.02.19 21:19, Collin Walling wrote: > >>> On 1/30/19 10:57 AM, David Hildenbrand wrote: > >>>> We decided to always create the PCI host bridge, even if 'zpci' is not > >>>> enabled (due to migration compatibility). This however right now allows > >>>> to add zPCI/PCI devices to a VM although the guest will never actually > >>>> see > >>>> them, confusing people that are using a simple CPU model that has no > >>>> 'zpci' enabled - "Why isn't this working" (David Hildenbrand) > >>>> > >>>> Let's check for 'zpci' and at least print a warning that this will not > >>>> work as expected. We could also bail out, however that might break > >>>> existing QEMU commandlines. > >>>> > >>>> Reviewed-by: Thomas Huth <th...@redhat.com> > >>>> Signed-off-by: David Hildenbrand <da...@redhat.com> > >>>> --- > >>>> hw/s390x/s390-pci-bus.c | 5 +++++ > >>>> 1 file changed, 5 insertions(+) > >>>> > >>>> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c > >>>> index 9b5c5fff60..2efd9186c2 100644 > >>>> --- a/hw/s390x/s390-pci-bus.c > >>>> +++ b/hw/s390x/s390-pci-bus.c > >>>> @@ -826,6 +826,11 @@ static void s390_pcihost_pre_plug(HotplugHandler > >>>> *hotplug_dev, DeviceState *dev, > >>>> { > >>>> S390pciState *s = S390_PCI_HOST_BRIDGE(hotplug_dev); > >>>> > >>>> + if (!s390_has_feat(S390_FEAT_ZPCI)) { > >>>> + warn_report("PCI/zPCI device without the 'zpci' CPU feature." > >>>> + " The guest will not be able to see/use this > >>>> device"); > >>>> + } > >>>> + > >>>> if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) { > >>>> PCIDevice *pdev = PCI_DEVICE(dev); > >>>> > >>>> > >>> > >>> I wonder if someone might misconstrue this as "the _PCI device_ needs > >>> the zpci feature." I think "'zpci' CPU feature required to support > >>> PCI/zPCI devices." reads better. The last sentence is fine to me. > >>> > >> > >> Well, the guest needs the 'zpci' feature to see the device. And that's > >> what that message says in my opinion. Not that a device needs to have a > >> feature (I added "CPU feature" for this reason). > >> > >> "required to support" does it not make very clear what we actually want > >> to say. > >> > >> Thanks! > >> > > > > I see your point. We can still plug in the device without the CPU > > feature, but the device will ultimately be useless to the guest. Thanks > > for clearing that up. > > > > Still, the wording reads strangely to me. I read it as the PCI device > > itself requires a "zpci CPU feature" which of course does not make sense > > (and I fully understand that's not what you mean here). > > > > What do you think about: > > > > "PCI/zPCI device plugging without 'zpci' CPU feature enabled." along > > with your second sentence, of course. > > "Plugging a PCI/zPCI device without the 'zpci' CPU feature enabled. The > guest will not be able to see/use this device." > > would make sense to me! Ok, I have now warn_report("Plugging a PCI/zPCI device without the 'zpci' CPU " "feature enabled; the guest will not be able to see/use " "this device"); > > > > > Either way you decide, it's still a good idea to have this warning in > > here. I'm really just debating syntax and not semantics, so it's not > > really important. I won't impede this patch over a differing opinion of > > a small rewording. :) > > > > Reviewed-by: Collin Walling <wall...@linux.ibm.com> > > > > Thanks! >