Re: [RFC v1 04/25] target/arm/kvm-rme: Add mechanic to initialize realms

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Mon, Jul 13, 2026 at 03:14:05PM +1000, Gavin Shan wrote:
> On 7/8/26 8:42 AM, Mathieu Poirier wrote:
> > From: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > 
> > Initialise an @rme_guest object and install a handler to get notified
> > when the Realm is ready to start.  That way we can finish reading the
> > Realm once we know everything is in place.
> > 
> > Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> > ---
> >   target/arm/kvm-rme.c  | 50 +++++++++++++++++++++++++++++++++++++++++++
> >   target/arm/kvm-stub.c |  5 +++++
> >   target/arm/kvm.c      |  7 +++++-
> >   target/arm/kvm_arm.h  |  9 ++++++++
> >   4 files changed, 70 insertions(+), 1 deletion(-)
> > 
> > diff --git a/target/arm/kvm-rme.c b/target/arm/kvm-rme.c
> > index 42e1d1e7b859..b86b9d6a25cb 100644
> > --- a/target/arm/kvm-rme.c
> > +++ b/target/arm/kvm-rme.c
> > @@ -13,6 +13,7 @@
> >   #include "kvm_arm.h"
> >   #include "migration/blocker.h"
> >   #include "qapi/error.h"
> > +#include "qemu/error-report.h"
> >   #include "qom/object_interfaces.h"
> >   #include "system/confidential-guest-support.h"
> >   #include "system/kvm.h"
> > @@ -29,14 +30,63 @@ OBJECT_DEFINE_SIMPLE_TYPE_WITH_INTERFACES(RmeGuest, rme_guest, RME_GUEST,
> >                                             CONFIDENTIAL_GUEST_SUPPORT,
> >                                             { TYPE_USER_CREATABLE }, { })
> > +static RmeGuest *rme_guest;
> > +
> > +static void rme_vm_state_change(void *opaque, bool running, RunState state)
> > +{
> > +    if (!running) {
> > +        return;
> > +    }
> > +
> > +    kvm_mark_guest_state_protected();
> > +}
> > +
> >   static void rme_guest_class_init(ObjectClass *oc, const void *data)
> >   {
> >   }
> >   static void rme_guest_init(Object *obj)
> >   {
> > +    if (rme_guest) {
> > +        error_report("a single instance of RmeGuest is supported");
> > +        exit(1);
> > +    }
> > +    rme_guest = RME_GUEST(obj);
> >   }
> >   static void rme_guest_finalize(Object *obj)
> >   {
> >   }
> > +
> > +int kvm_arm_rme_init(MachineState *ms, KVMState *s)
> > +{
> > +    static Error *rme_mig_blocker;
> > +    ConfidentialGuestSupport *cgs = ms->cgs;
> > +
> > +    if (!rme_guest) {
> > +        return 0;
> > +    }
> > +
> > +    if (!cgs) {
> > +        error_report("missing -machine confidential-guest-support parameter");
> > +        return -EINVAL;
> > +    }
> > +
> > +    if (!kvm_vm_check_extension(s, KVM_CAP_ARM_RMI)) {
> > +        error_report("KVM doesn't support Realms");
> > +        return -ENODEV;
> > +    }
> > +
> > +    error_setg(&rme_mig_blocker, "RME: migration is not implemented");
> > +    migrate_add_blocker(&rme_mig_blocker, &error_fatal);
> > +
> > +    /*
> > +     * The realm activation is done last, when the VM starts, after all images
> > +     * have been loaded and all vcpus finalized.
> > +     */
> > +    qemu_add_vm_change_state_handler(rme_vm_state_change, NULL);
> > +
> > +    cgs->require_guest_memfd = true;
> > +    cgs->ready = true;
> > +    return 0;
> > +}
> 
> I think it's more reasonable to set ConfidentialGuestSupportClass::kvm_init to
> kvm_arm_rme_init in rme_guest_class_init(). confidential_guest_kvm_init()
> gets called in target/arm/kvm.c::kvm_arch_init(). With this, the pattern matches
> with that for x86.

I agree, it would be nice to align Arm with the other architectures that
support confidential guests.  Let me see what I can do.

Thanks for the review, I'll look at your other comment tomorrow.

Mathieu

> 
> More details can be found from commit 631a2ac5a4be ("i386/tdx: Implement tdx_kvm_init()
> to initialize TDX VM context").
> 
> Thanks,
> Gavin
> 
> > diff --git a/target/arm/kvm-stub.c b/target/arm/kvm-stub.c
> > index 88cbe8d85c41..eec1ca3dd2e5 100644
> > --- a/target/arm/kvm-stub.c
> > +++ b/target/arm/kvm-stub.c
> > @@ -119,3 +119,8 @@ char *kvm_print_register_name(uint64_t regidx)
> >   {
> >       g_assert_not_reached();
> >   }
> > +
> > +int kvm_arm_rme_init(MachineState *ms, KVMState *s)
> > +{
> > +    g_assert_not_reached();
> > +}
> > diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> > index ed99be7fd80c..28d5643d6779 100644
> > --- a/target/arm/kvm.c
> > +++ b/target/arm/kvm.c
> > @@ -660,7 +660,12 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
> >       hw_breakpoints = g_array_sized_new(true, true,
> >                                          sizeof(HWBreakpoint), max_hw_bps);
> > -    return 0;
> > +    ret = kvm_arm_rme_init(ms, s);
> > +    if (ret) {
> > +        error_report("Failed to enable RME: %s", strerror(-ret));
> > +    }
> > +
> > +    return ret;
> >   }
> >   unsigned long kvm_arch_vcpu_id(CPUState *cpu)
> > diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
> > index e7c40fb003e4..6d058b0e08a2 100644
> > --- a/target/arm/kvm_arm.h
> > +++ b/target/arm/kvm_arm.h
> > @@ -240,4 +240,13 @@ void arm_gic_cap_kvm_probe(GICCapability *v2, GICCapability *v3);
> >    */
> >   char *kvm_print_register_name(uint64_t regidx);
> > +/**
> > + * kvm_arm_rme_init
> > + * @ms: the machine state
> > + * @s: State of KVM
> > + *
> > + * Prepare the machine to be a Realm, if the user enabled it.
> > + */
> > +int kvm_arm_rme_init(MachineState *ms, KVMState *s);
> > +
> >   #endif
>