[Qemu-devel] [PATCH v1] s390x/pci: Warn when adding PCI devices without the 'zpci' feature

[David Hildenbrand <david@redhat.com>]

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.

Signed-off-by: David Hildenbrand <david@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 b86a8bdcd4..e7d4f49611 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -863,6 +863,11 @@ 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("Adding PCI or zPCI devices without the 'zpci' CPU feature."
+                    " The guest will not be able to see/use these devices.");
+    }
+
     if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) {
         PCIDevice *pdev = PCI_DEVICE(dev);
 
-- 
2.17.2