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

[Daniel P . Berrangé]

On Tue, Jan 12, 2021 at 12:36:07PM +0100, 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.

Except TYPE_CONFIDENTIAL_GUEST_SUPPORT is declared as an object, not
an interface. Clearly something in this series is wrong though, as
the ppc impl uses it as if it were an interface. 

Regards,
Daniel
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