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

[Christian Borntraeger]

On 13.01.21 01:57, David Gibson wrote:
> On Tue, Jan 12, 2021 at 12:36:07PM +0100, Cornelia Huck wrote:
> 65;6201;1c> 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.
> 
> No, that was true of an earlier revision, but parent is correct in the
> current version.

right now parent is obviously wrong as it triggers the above warning (and all 
other
variants in the previous patches also use TYPE_OBJECT). It is probably the right
thing when you fix

+struct S390PVGuestState {
+    Object parent_obj;
+};
+

and change Object to the proper type I guess.