s390x/pci: Warn when adding PCI devices without the 'zpci' feature

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 <thuth@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20190130155733.32742-4-david@redhat.com>
Reviewed-by: Collin Walling <walling@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index d85bc3461729dbba7e0cf65b38f8994ee3078769..3816fb1f11bba8403b39cab24ea8d9637d14f892 100644 (file)
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -860,6 +860,12 @@ 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("Plugging a PCI/zPCI device without the 'zpci' CPU "
+                    "feature enabled; 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);