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

[Gavin Shan <gshan@redhat.com>]

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.

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