Re: [Qemu-devel] [qemu-s390x] [PATCH v2 3/6] s390x/pci: Warn when adding PCI devices without the 'zpci' feature

[David Hildenbrand <david@redhat.com>]

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 <thuth@redhat.com>
>> 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 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!

-- 

Thanks,

David / dhildenb