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

[David Gibson]

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.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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