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

[David Gibson]

On Wed, Jan 13, 2021 at 07:57:41AM +0100, Christian Borntraeger wrote:
> 
> 
> 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. 

Yes, I think so.  In the next spin I've fixed the parent_obj field (as
well as moving to OBJECT_DEFINE_TYPE()) and it's passing the gitlab
CI, at least.

-- 
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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