Re: [PATCH v6 13/13] s390: Recognize confidential-guest-support option

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 12.01.21 12:36, Cornelia Huck wrote:
> On Tue, 12 Jan 2021 09:15:26 +0100
> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> 
>> On 12.01.21 05:45, David Gibson wrote:
>>> At least some s390 cpu models support "Protected Virtualization" (PV),
>>> a mechanism to protect guests from eavesdropping by a compromised
>>> hypervisor.
>>>
>>> This is similar in function to other mechanisms like AMD's SEV and
>>> POWER's PEF, which are controlled by the "confidential-guest-support"
>>> machine option.  s390 is a slightly special case, because we already
>>> supported PV, simply by using a CPU model with the required feature
>>> (S390_FEAT_UNPACK).
>>>
>>> To integrate this with the option used by other platforms, we
>>> implement the following compromise:
>>>
>>>  - When the confidential-guest-support option is set, s390 will
>>>    recognize it, verify that the CPU can support PV (failing if not)
>>>    and set virtio default options necessary for encrypted or protected
>>>    guests, as on other platforms.  i.e. if confidential-guest-support
>>>    is set, we will either create a guest capable of entering PV mode,
>>>    or fail outright.
>>>
>>>  - If confidential-guest-support is not set, guests might still be
>>>    able to enter PV mode, if the CPU has the right model.  This may be
>>>    a little surprising, but shouldn't actually be harmful.
>>>
>>> To start a guest supporting Protected Virtualization using the new
>>> option use the command line arguments:
>>>     -object s390-pv-guest,id=pv0 -machine confidential-guest-support=pv0  
>>
>>
>> This results in
>>
>> [cborntra@t35lp61 qemu]$ qemu-system-s390x -enable-kvm -nographic -m 2G -kernel ~/full.normal 
>> **
>> ERROR:../qom/object.c:317:type_initialize: assertion failed: (parent->instance_size <= ti->instance_size)
>> Bail out! ERROR:../qom/object.c:317:type_initialize: assertion failed: (parent->instance_size <= ti->instance_size)
>> Aborted (core dumped)
>>
> 
>>> +static const TypeInfo s390_pv_guest_info = {
>>> +    .parent = TYPE_CONFIDENTIAL_GUEST_SUPPORT,
>>> +    .name = TYPE_S390_PV_GUEST,
>>> +    .instance_size = sizeof(S390PVGuestState),
>>> +    .interfaces = (InterfaceInfo[]) {
>>> +        { TYPE_USER_CREATABLE },
>>> +        { }
>>> +    }
>>> +};
> 
> I think this needs TYPE_OBJECT in .parent and
> TYPE_CONFIDENTIAL_GUEST_SUPPORT as an interface to fix the crash.

It fixes the crash but it does not work:
qemu-system-s390x -enable-kvm -nographic -m 2G -kernel ~/image   -object s390-pv-guest,id=pv0 -machine confidential-guest-support=pv0
qemu-system-s390x: Invalid parameter type for 'confidential-guest-support', expected: confidential-guest-support