Re: [RFC v4 03/24] target/arm: Add confidential guest support

[Kohei Enju <enju.kohei@fujitsu.com>]

On 09/22 10:01, Lorenzo Pieralisi wrote:
> On Tue, Sep 15, 2026 at 04:27:21PM -0500, Michael Roth wrote:
> > On Thu, Sep 03, 2026 at 01:35:50PM -0600, Mathieu Poirier wrote:
> > > From: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > > 
> > > Add a new RmeGuest object, inheriting from ConfidentialGuestSupport, to
> > > support the Arm Realm Management Extension (RME). It is instantiated by
> > > passing on the command-line:
> > > 
> > >   -M virt,confidential-guest-support=<id>
> > >   -object rme-guest,id=<id>
> > > 
> > > This is only the skeleton. Support will be added in following patches.
> > > 
> > > Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > > Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> > > ---
> > >  docs/system/confidential-guest-support.rst |  1 +
> > >  qapi/qom.json                              | 13 +++++++
> > >  target/arm/kvm-rme.c                       | 42 ++++++++++++++++++++++
> > >  target/arm/meson.build                     |  5 ++-
> > >  4 files changed, 60 insertions(+), 1 deletion(-)
> > >  create mode 100644 target/arm/kvm-rme.c
> > > 
> > > diff --git a/docs/system/confidential-guest-support.rst b/docs/system/confidential-guest-support.rst
> > > index 562a7c3c2852..abb56923ad13 100644
> > > --- a/docs/system/confidential-guest-support.rst
> > > +++ b/docs/system/confidential-guest-support.rst
> > > @@ -42,5 +42,6 @@ Currently supported confidential guest mechanisms are:
> > >  * POWER Protected Execution Facility (PEF) (see :ref:`power-papr-protected-execution-facility-pef`)
> > >  * s390x Protected Virtualization (PV) (see :doc:`s390x/protvirt`)
> > >  * AWS Nitro Enclaves (see :doc:`nitro`)
> > > +* Arm Realm Management Extension (RME)
> > >  
> > >  Other mechanisms may be supported in future.
> > > diff --git a/qapi/qom.json b/qapi/qom.json
> > > index 776b13027fd8..52997c29a32d 100644
> > > --- a/qapi/qom.json
> > > +++ b/qapi/qom.json
> > > @@ -1288,6 +1288,17 @@
> > >    'data': { '*pretty': 'bool',
> > >              '*close-action': 'MonitorQMPCloseAction' } }
> > >  
> > > +##
> > > +# @RmeGuestProperties:
> > > +#
> > > +# Properties for rme-guest objects.
> > > +#
> > > +# Since: 11.1
> > > +##
> > > +{ 'struct': 'RmeGuestProperties',
> > > +  'base': 'ConfidentialGuestSupportProperties',
> > 
> > Just FYI, based on input from Markus I'm planning to drop this
> > ConfidentialGuestSupportProperties base type from my series
> > since it's probably only SNP/TDX that need to be able to switch
> > it on/off, whereas this series appears to use/require it from
> > the start.
> > 
> > I'm not exactly sure what it will look like for v3 yet, but if you
> > were based on v2 you'd instead probably just do the following in the
> > instance_init function for your rme-guest instance:
> > 
> >   cgs->allow_convert_in_place = true;
> >   cgs->convert_in_place = true;
> > 
> > rather than exposing it as a cmdline option.
> 
> Yep, it won't be an option for CCA Realms anyway since that will be
> the baseline.

IIUC, in-place conversion requires RAM backed by a shared/mappable
guest_memfd. If in-place conversion is always enabled for CCA Realms,
could QEMU also select the equivalent of

  -object memory-backend-guest-memfd,id=ram0,size=...,share=on

automatically for the default RAM, so that specifying the RAM size with
`-m` is sufficient?

Thanks,
Kohei

> 
> Thanks,
> Lorenzo
> 
> > Thanks,
> > 
> > Mike
> > 
> > > +  'data': {} }
> > > +
> > >  ##
> > >  # @ObjectType:
> > >  #
> > > @@ -1346,6 +1357,7 @@
> > >      { 'name': 'pr-manager-helper',
> > >        'if': 'CONFIG_LINUX' },
> > >      'qtest',
> > > +    'rme-guest',
> > >      'rng-builtin',
> > >      'rng-egd',
> > >      { 'name': 'rng-random',
> > > @@ -1427,6 +1439,7 @@
> > >        'pr-manager-helper':          { 'type': 'PrManagerHelperProperties',
> > >                                        'if': 'CONFIG_LINUX' },
> > >        'qtest':                      'QtestProperties',
> > > +      'rme-guest':                  'RmeGuestProperties',
> > >        'rng-builtin':                'RngProperties',
> > >        'rng-egd':                    'RngEgdProperties',
> > >        'rng-random':                 { 'type': 'RngRandomProperties',
> > > diff --git a/target/arm/kvm-rme.c b/target/arm/kvm-rme.c
> > > new file mode 100644
> > > index 000000000000..42e1d1e7b859
> > > --- /dev/null
> > > +++ b/target/arm/kvm-rme.c
> > > @@ -0,0 +1,42 @@
> > > +/*
> > > + * QEMU Arm RME support
> > > + *
> > > + * SPDX-License-Identifier: GPL-2.0-or-later
> > > + *
> > > + * Copyright Linaro 2026
> > > + */
> > > +
> > > +#include "qemu/osdep.h"
> > > +
> > > +#include "hw/core/boards.h"
> > > +#include "hw/core/cpu.h"
> > > +#include "kvm_arm.h"
> > > +#include "migration/blocker.h"
> > > +#include "qapi/error.h"
> > > +#include "qom/object_interfaces.h"
> > > +#include "system/confidential-guest-support.h"
> > > +#include "system/kvm.h"
> > > +#include "system/runstate.h"
> > > +
> > > +#define TYPE_RME_GUEST "rme-guest"
> > > +OBJECT_DECLARE_SIMPLE_TYPE(RmeGuest, RME_GUEST)
> > > +
> > > +struct RmeGuest {
> > > +    ConfidentialGuestSupport parent_obj;
> > > +};
> > > +
> > > +OBJECT_DEFINE_SIMPLE_TYPE_WITH_INTERFACES(RmeGuest, rme_guest, RME_GUEST,
> > > +                                          CONFIDENTIAL_GUEST_SUPPORT,
> > > +                                          { TYPE_USER_CREATABLE }, { })
> > > +
> > > +static void rme_guest_class_init(ObjectClass *oc, const void *data)
> > > +{
> > > +}
> > > +
> > > +static void rme_guest_init(Object *obj)
> > > +{
> > > +}
> > > +
> > > +static void rme_guest_finalize(Object *obj)
> > > +{
> > > +}
> > > diff --git a/target/arm/meson.build b/target/arm/meson.build
> > > index 0369f96b4cc6..9d322a7aad28 100644
> > > --- a/target/arm/meson.build
> > > +++ b/target/arm/meson.build
> > > @@ -31,7 +31,10 @@ arm_common_user_system_ss.add(when: 'TARGET_AARCH64', if_true: files(
> > >  arm_common_system_ss.add(files(
> > >    'arm-qmp-cmds.c',
> > >  ))
> > > -arm_system_ss.add(when: 'CONFIG_KVM', if_true: files('hyp_gdbstub.c', 'kvm.c'))
> > > +arm_system_ss.add(when: 'CONFIG_KVM', if_true: files(
> > > +  'hyp_gdbstub.c',
> > > +  'kvm.c',
> > > +  'kvm-rme.c'))
> > >  arm_system_ss.add(when: 'CONFIG_HVF', if_true: files('hyp_gdbstub.c'))
> > >  
> > >  arm_user_ss.add(files('cpu.c'))
> > > -- 
> > > 2.43.0
> > > 
> > >