Re: [PATCH v6 10/13] spapr: Add PEF based confidential guest support

[Daniel P . Berrangé]

On Tue, Jan 12, 2021 at 03:45:05PM +1100, David Gibson wrote:
> Some upcoming POWER machines have a system called PEF (Protected
> Execution Facility) which uses a small ultravisor to allow guests to
> run in a way that they can't be eavesdropped by the hypervisor.  The
> effect is roughly similar to AMD SEV, although the mechanisms are
> quite different.
> 
> Most of the work of this is done between the guest, KVM and the
> ultravisor, with little need for involvement by qemu.  However qemu
> does need to tell KVM to allow secure VMs.
> 
> Because the availability of secure mode is a guest visible difference
> which depends on having the right hardware and firmware, we don't
> enable this by default.  In order to run a secure guest you need to
> create a "pef-guest" object and set the confidential-guest-support
> property to point to it.
> 
> Note that this just *allows* secure guests, the architecture of PEF is
> such that the guest still needs to talk to the ultravisor to enter
> secure mode.  Qemu has no directl way of knowing if the guest is in
> secure mode, and certainly can't know until well after machine
> creation time.
> 
> To start a PEF-capable guest, use the command line options:
>     -object pef-guest,id=pef0 -machine confidential-guest-support=pef0
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  docs/confidential-guest-support.txt |   2 +
>  docs/papr-pef.txt                   |  30 ++++++++
>  hw/ppc/meson.build                  |   1 +
>  hw/ppc/pef.c                        | 115 ++++++++++++++++++++++++++++
>  hw/ppc/spapr.c                      |  10 +++
>  include/hw/ppc/pef.h                |  26 +++++++
>  target/ppc/kvm.c                    |  18 -----
>  target/ppc/kvm_ppc.h                |   6 --
>  8 files changed, 184 insertions(+), 24 deletions(-)
>  create mode 100644 docs/papr-pef.txt
>  create mode 100644 hw/ppc/pef.c
>  create mode 100644 include/hw/ppc/pef.h
> 

> +static const TypeInfo pef_guest_info = {
> +    .parent = TYPE_OBJECT,
> +    .name = TYPE_PEF_GUEST,
> +    .instance_size = sizeof(PefGuestState),
> +    .interfaces = (InterfaceInfo[]) {
> +        { TYPE_CONFIDENTIAL_GUEST_SUPPORT },
> +        { TYPE_USER_CREATABLE },
> +        { }
> +    }
> +};

IIUC, the earlier patch defines TYPE_CONFIDENTIAL_GUEST_SUPPORT
as a object, but you're using it as an interface here. The later
s390 patch uses it as a parent, which makes more sense given it
is a declared as an object.


Regards,
Daniel
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