Re: [Qemu-devel] [qemu-s390x] [PATCH v8 4/6] s390x/ap: base Adjunct Processor (AP) object model

[Christian Borntraeger]

On 09/13/2018 07:48 AM, Thomas Huth wrote:
> On 2018-09-12 22:08, Tony Krowiak wrote:
>> From: Tony Krowiak <address@hidden>
>>
>> Introduces the base object model for virtualizing AP devices.
>>
>> Signed-off-by: Tony Krowiak <address@hidden>
>> ---
> [...]
>> diff --git a/hw/s390x/ap-bridge.c b/hw/s390x/ap-bridge.c
>> new file mode 100644
>> index 0000000..4f10425
>> --- /dev/null
>> +++ b/hw/s390x/ap-bridge.c
> [...]
>> +void s390_init_ap(void)
>> +{
>> +    DeviceState *dev;
>> +
>> +    /* Create bridge device */
>> +    dev = qdev_create(NULL, TYPE_AP_BRIDGE);
>> +    object_property_add_child(qdev_get_machine(), TYPE_AP_BRIDGE,
>> +                              OBJECT(dev), NULL);
>> +    qdev_init_nofail(dev);
>> +
>> +    /* Create bus on bridge device */
>> +    qbus_create(TYPE_VFIO_AP_BUS, dev, TYPE_VFIO_AP_BUS);
>> + }
> [...]
>> +type_init(ap_device_register)
>> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
>> index f0f7fdc..3c100c2 100644
>> --- a/hw/s390x/s390-virtio-ccw.c
>> +++ b/hw/s390x/s390-virtio-ccw.c
>> @@ -32,6 +32,7 @@
>>  #include "ipl.h"
>>  #include "hw/s390x/s390-virtio-ccw.h"
>>  #include "hw/s390x/css-bridge.h"
>> +#include "hw/s390x/ap-bridge.h"
>>  #include "migration/register.h"
>>  #include "cpu_models.h"
>>  #include "hw/nmi.h"
>> @@ -263,6 +264,9 @@ static void ccw_init(MachineState *machine)
>>      /* init the SIGP facility */
>>      s390_init_sigp();
>>  
>> +    /* create AP bridge and bus(es) */
>> +    s390_init_ap();
>> +
> 
> Not sure since there is no explicit migration state involved here, but I
> think you cannot simply create the ap-bridge device always
> unconditionally, can you? Did you check whether you can ping-pong
> migrate an guest that runs on an older version of QEMU to a QEMU that
> contains this patch and back? If it does not work, it might be necessary
> to restrict this ap-bridge device for new machine types only, I think.

We have already the cpu features at this point in time. So simply doing
s390_has_feat(S390_FEAT_AP) in s390_init_ap ?