Re: [PATCH 02/11] KVM: arm64: CCA: Introduce Realms

[Steven Price <steven.price@arm.com>]

On 03/11/2026 11:34, Suzuki K Poulose wrote:
> Hi Steven
> 
> On 02/11/2026 14:12, Steven Price wrote:
>> From: Suzuki K Poulose <suzuki.poulose@arm.com>
>>
>> Add foundational work for supporting Realms.
>>   - Add a new VM flavor.
>>   - At KVM init, check if the KVM can support Realms (though not
>> functional
>>     yet) and will be advertised by static key kvm_rmi_is_available. This
>>     will be turned on in a later patch, once we have all the bits and
>>     pieces ready. For now check if we are blessed with KVM_MODE_RMM.
>>   - Add realm specific tracking in kvm_arch. Since Realm and protected
>> pKVM
>>     states are mutually exclusive, move them into a union.
> 
> I think this patch could stop with the above items.
> 
>>   - Also adjust the memslot preparation checks to reflect the changes.
>>
> 
> This and the VCPU features could be a separate patch or merged with the
> other patches.

Yes I think you're right - this patch has got too big. I'll split out
the kvm_init_rmi() parts to a separate patch.

>> Please note that we cannot create Realm VMs yet. This requires further
>> changes to the UABI and core RMI driver support, which will come later.
>>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> ---
>>   arch/arm64/include/asm/kvm_emulate.h   | 16 +++++++
>>   arch/arm64/include/asm/kvm_host.h      | 57 +++++++++++++++++-------
>>   arch/arm64/include/asm/kvm_rmi.h       | 61 ++++++++++++++++++++++++++
>>   arch/arm64/include/asm/virt.h          |  1 +
>>   arch/arm64/kvm/Makefile                |  2 +-
>>   arch/arm64/kvm/arm.c                   | 24 ++++++++--
>>   arch/arm64/kvm/hyp/include/nvhe/pkvm.h |  2 +-
>>   arch/arm64/kvm/hyp/nvhe/switch.c       |  4 +-
>>   arch/arm64/kvm/hyp/nvhe/timer-sr.c     |  2 +-
>>   arch/arm64/kvm/mmu.c                   | 13 +++---
>>   arch/arm64/kvm/rmi.c                   | 18 ++++++++
>>   11 files changed, 169 insertions(+), 31 deletions(-)
>>   create mode 100644 arch/arm64/include/asm/kvm_rmi.h
>>   create mode 100644 arch/arm64/kvm/rmi.c
>>
>> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/
>> include/asm/kvm_emulate.h
>> index 334211b8b2ee..32021bdf2610 100644
>> --- a/arch/arm64/include/asm/kvm_emulate.h
>> +++ b/arch/arm64/include/asm/kvm_emulate.h
>> @@ -831,4 +831,20 @@ static inline void kvm_reset_vcpu_psci(struct
>> kvm_vcpu *vcpu,
>>       vcpu_set_reg(vcpu, 0, reset_state->r0);
>>   }
>>   +static inline enum realm_state kvm_realm_state(struct kvm *kvm)
>> +{
>> +    return READ_ONCE(kvm->arch.realm.state);
>> +}
>> +
>> +static inline void kvm_set_realm_state(struct kvm *kvm,
>> +                       enum realm_state new_state)
>> +{
>> +    WRITE_ONCE(kvm->arch.realm.state, new_state);
>> +}
>> +
>> +static inline bool kvm_realm_is_created(struct kvm *kvm)
>> +{
>> +    return kvm_vm_is_realm(kvm) && kvm_realm_state(kvm) !=
>> REALM_STATE_NONE;
>> +}
>> +
> 
> 
>>   #endif /* __ARM64_KVM_EMULATE_H__ */
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/
>> asm/kvm_host.h
>> index ccd2dc8f73c3..7d0222047ca1 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -29,6 +29,7 @@
>>   #include <asm/kvm.h>
>>   #include <asm/kvm_asm.h>
>>   #include <asm/kvm_hcall.h>
>> +#include <asm/kvm_rmi.h>
>>   #include <asm/vncr_mapping.h>
>>     #define __KVM_HAVE_ARCH_INTC_INITIALIZED
>> @@ -48,6 +49,13 @@
>>   #define KVM_VCPU_MAX_FEATURES 10
>>   #define KVM_VCPU_VALID_FEATURES    (BIT(KVM_VCPU_MAX_FEATURES) - 1)
>>   
> 
> 
>> +#define KVM_REALM_VCPU_VALID_FEATURES            \
>> +    (BIT(KVM_ARM_VCPU_POWER_OFF)        |    \
>> +     BIT(KVM_ARM_VCPU_PSCI_0_2)        |    \
>> +     BIT(KVM_ARM_VCPU_PTRAUTH_ADDRESS)    |    \
>> +     BIT(KVM_ARM_VCPU_SVE)            |    \
>> +     BIT(KVM_ARM_VCPU_PTRAUTH_GENERIC))
>> +
> 
> Please could we move the ^^ to a separate patch ? See more below.

Indeed - they shouldn't really be here but should be in a later series.

>>   #define KVM_REQ_SLEEP \
>>       KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
>>   #define KVM_REQ_IRQ_PENDING        KVM_ARCH_REQ(1)
>> @@ -409,6 +417,7 @@ enum kvm_arm_vm_flavor {
>>       VM_PKVM,        /* Normal guests on pKVM */
>>       MARKER(__VM_PROTECTED),
>>       VM_PROTECTED_PKVM,    /* Protected VM */
>> +    VM_REALM,        /* CCA */
>>       VM_FLAVOR_MAX
>>   };
>>   @@ -502,11 +511,14 @@ struct kvm_arch {
>>       /* Count the number of VNCR_EL2 TLBs */
>>       atomic_t vncr_tlb_count;
>>   -    /*
>> -     * For an untrusted host VM, 'pkvm.handle' is used to lookup
>> -     * the associated pKVM instance in the hypervisor.
>> -     */
>> -    struct kvm_protected_vm pkvm;
>> +    union {
>> +        /*
>> +         * For an untrusted host VM, 'pkvm.handle' is used to lookup
>> +         * the associated pKVM instance in the hypervisor.
>> +         */
>> +        struct kvm_protected_vm pkvm;
>> +        struct realm realm;
>> +    };
>>     #ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
>>       /* Nested virtualization info */
>> @@ -1572,30 +1584,43 @@ struct kvm *kvm_arch_alloc_vm(void);
>>     #define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS_RANGE
>>   -#ifdef __KVM_NVHE_HYPERVISOR__
>> +#define kvm_vm_is_protected(kvm)    ((kvm)->arch.vm_flavor >=
>> __VM_PROTECTED)
>>   -#define kvm_vm_is_protected(kvm)            \
>> -    (is_protected_kvm_enabled() && ((kvm)->arch.vm_flavor ==
>> VM_PROTECTED_PKVM))
>> +#ifdef __KVM_NVHE_HYPERVISOR__
>>   /*
>>    * Accessing vcpu->kvm from nVHE hyp stub is tricky, as we need to
>> convert the
>>    * pointer to the hyp VA. With pKVM, the nVHE code runs with the
>> hyp_vcpu,
>> - * which is populated correctly and is gated on
>> is_protected_kvm_enabled().
>> + * which is populated correctly. Always vcpu_is_protected_pkvm(),
>> which is
>> + * gated on is_protected_kvm_enabled().
>> + */
>> +#define vcpu_is_protected(vcpu)        BUILD_BUG_ON(1)
>> +#else
>> +#define vcpu_is_protected(vcpu)        kvm_vm_is_protected((vcpu)->kvm)
>> +#endif
>> +
>> +#define kvm_vm_is_protected_pkvm(kvm)                    \
>> +    (is_protected_kvm_enabled() && ((kvm)->arch.vm_flavor ==
>> VM_PROTECTED_PKVM))
>> +
>> +/*
>> + * Rely on is_protected_kvm_enabled() check in
>> kvm_vm_is_protected_pkvm() to
>> + * make sure the vcpu->kvm is always valid VA in the context
>>    */
>> -#define vcpu_is_protected(vcpu)                        \
>> +#define vcpu_is_protected_pkvm(vcpu)                    \
>>       ({                                \
>>           struct kvm *__kvm = READ_ONCE((vcpu)->kvm);        \
>>                                       \
>> -        (__kvm && kvm_vm_is_protected(__kvm));            \
>> +        (__kvm && kvm_vm_is_protected_pkvm(__kvm));        \
>>       })
>>   -#else
>> -
>> -#define kvm_vm_is_protected(kvm)    ((kvm)->arch.vm_flavor >=
>> __VM_PROTECTED)
>> -#define vcpu_is_protected(vcpu)        kvm_vm_is_protected((vcpu)->kvm)
>> +#define kvm_vm_is_realm(kvm)        ((kvm)->arch.vm_flavor == VM_REALM)
>> +#define vcpu_is_rec(vcpu)        kvm_vm_is_realm((vcpu)->kvm)
>>     #define kvm_vm_hyp_is_distrusting(kvm)    ((kvm)->arch.vm_flavor
>> >= __VM_DISTRUSTING_HYP)
>>   -#endif    /* __KVM_NVHE_HYPERVISOR__ */
>> +#define kvm_arch_has_private_mem(kvm) kvm_vm_is_realm(kvm)
>> +
>> +int kvm_arm_vcpu_finalize(struct kvm_vcpu *vcpu, int feature);
>> +bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
>>     #define kvm_has_mte(kvm)                    \
>>       (system_supports_mte() &&                \
>> diff --git a/arch/arm64/include/asm/kvm_rmi.h b/arch/arm64/include/
>> asm/kvm_rmi.h
>> new file mode 100644
>> index 000000000000..3194daaacf2b
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/kvm_rmi.h
>> @@ -0,0 +1,61 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * Copyright (C) 2023-2026 ARM Ltd.
>> + */
>> +
>> +#ifndef __ASM_KVM_RMI_H
>> +#define __ASM_KVM_RMI_H
>> +
>> +/**
>> + * enum realm_state - State of a Realm
>> + *
>> + * Mirrors the RMM's Realm lifecycle states where they are meaningful
>> to KVM,
>> + * with REALM_STATE_DYING being a KVM-internal state used to prevent
>> further
>> + * requests while teardown is in progress. KVM does not track
>> REALM_SYSTEM_OFF
>> + * or REALM_ZOMBIE separately as they naturally lead to teardown.
>> + */
>> +enum realm_state {
>> +    /**
>> +     * @REALM_STATE_NONE:
>> +     *      Realm has not yet been created. rmi_realm_create() has not
>> +     *      yet been called.
>> +     */
>> +    REALM_STATE_NONE,
>> +    /**
>> +     * @REALM_STATE_NEW:
>> +     *      Realm is under construction, Realm Descriptor has been
>> created,
>> +     *      but it is not yet activated. Memory may be populated.
>> +     */
>> +    REALM_STATE_NEW,
>> +    /**
>> +     * @REALM_STATE_ACTIVE:
>> +     *      Realm has been created and is eligible for execution with
>> +     *      rmi_rec_enter(). Memory may no longer be populated with
>> known
>> +     *    contents.
>> +     */
>> +    REALM_STATE_ACTIVE,
>> +    /**
>> +     * @REALM_STATE_DYING:
>> +     *      Realm is in the process of being destroyed or has already
>> been
>> +     *      destroyed.
>> +     */
>> +    REALM_STATE_DYING,
>> +    /**
>> +     * @REALM_STATE_DEAD:
>> +     *      Realm has been destroyed.
>> +     */
>> +    REALM_STATE_DEAD
>> +};
>> +
>> +/**
>> + * struct realm - Additional per VM data for a Realm
>> + *
>> + * @state: The lifetime state machine for the realm
>> + */
>> +struct realm {
>> +    enum realm_state state;
>> +};
>> +
>> +void kvm_init_rmi(void);
>> +
>> +#endif /* __ASM_KVM_RMI_H */
>> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/
>> virt.h
>> index b546703c3ab9..92cec42952f4 100644
>> --- a/arch/arm64/include/asm/virt.h
>> +++ b/arch/arm64/include/asm/virt.h
>> @@ -87,6 +87,7 @@ void __hyp_reset_vectors(void);
>>   bool is_kvm_arm_initialised(void);
>>     DECLARE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
>> +DECLARE_STATIC_KEY_FALSE(kvm_rmi_is_available);
>>     static inline bool is_pkvm_initialized(void)
>>   {
>> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
>> index 7aaeeb84e788..66a719ab5b6b 100644
>> --- a/arch/arm64/kvm/Makefile
>> +++ b/arch/arm64/kvm/Makefile
>> @@ -16,7 +16,7 @@ CFLAGS_handle_exit.o += -Wno-override-init
>>   kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
>>        inject_fault.o va_layout.o handle_exit.o config.o \
>>        guest.o debug.o reset.o sys_regs.o stacktrace.o \
>> -     vgic-sys-reg-v3.o fpsimd.o pkvm.o \
>> +     vgic-sys-reg-v3.o fpsimd.o pkvm.o rmi.o \
>>        arch_timer.o trng.o vmid.o emulate-nested.o nested.o at.o \
>>        vgic/vgic.o vgic/vgic-init.o \
>>        vgic/vgic-irqfd.o vgic/vgic-v2.o \
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index 157bf4b81202..c8599fed5902 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -42,6 +42,7 @@
>>   #include <asm/kvm_nested.h>
>>   #include <asm/kvm_pkvm.h>
>>   #include <asm/kvm_ptrauth.h>
>> +#include <asm/kvm_rmi.h>
>>   #include <asm/sections.h>
>>   #include <asm/stacktrace/nvhe.h>
>>   @@ -112,6 +113,8 @@ long kvm_get_cap_for_kvm_ioctl(unsigned int
>> ioctl, long *ext)
>>       return -EINVAL;
>>   }
>>   +DEFINE_STATIC_KEY_FALSE(kvm_rmi_is_available);
>> +
>>   DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
>>     DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_base);
>> @@ -1732,10 +1735,19 @@ static unsigned long
>> system_supported_vcpu_features(struct kvm_vcpu *vcpu)
>>   {
>>       unsigned long features = KVM_VCPU_VALID_FEATURES;
>>   -    if (vcpu->kvm->arch.vm_flavor == VM_PROTECTED_PKVM)
>> +    switch (vcpu->kvm->arch.vm_flavor) {
>> +    case VM_PROTECTED_PKVM:
>>           kvm_pkvm_vcpu_allowed_features(vcpu->kvm, &features);
>> +        break;
>> +    case VM_REALM:
>> +        features = KVM_REALM_VCPU_VALID_FEATURES;
>> +        break;
>> +    default:
>> +        break;
>> +    }
> 
> This could be a separate patch ?

Agreed

>>   -    if (!cpus_have_final_cap(ARM64_HAS_32BIT_EL1))
>> +    if (vcpu_is_protected(vcpu) ||
>> +        !cpus_have_final_cap(ARM64_HAS_32BIT_EL1))
>>           clear_bit(KVM_ARM_VCPU_EL1_32BIT, &features);
> 
> We start with the allowed features and 32_BIT_EL1 is already cleared for
> both protected VMs. So we don't need this change anymore.

Ack

>>         if (!kvm_supports_guest_pmuv3()) {
>> @@ -1751,7 +1763,8 @@ static unsigned long
>> system_supported_vcpu_features(struct kvm_vcpu *vcpu)
>>           clear_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, &features);
>>       }
>>   -    if (!cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
>> +    if (vcpu_is_protected(vcpu) ||
>> +        !cpus_have_final_cap(ARM64_HAS_NESTED_VIRT))
>>           clear_bit(KVM_ARM_VCPU_HAS_EL2, &features);
>>   
> 
> Same as above
> 
>>       return features;
>> @@ -1775,7 +1788,7 @@ static int kvm_vcpu_init_check_features(struct
>> kvm_vcpu *vcpu,
>>       if (features & ~system_supported_vcpu_features(vcpu))
>>           return -EINVAL;
>>   -    /* EL2 implements PSCI 1.1; the host must not dispatch as 0.1. */
>> +    /* Both pKVM and RMM implements PSCI 1.1; the host must not
>> dispatch as 0.1. */
>>       if (vcpu_is_protected(vcpu) &&
>>           !test_bit(KVM_ARM_VCPU_PSCI_0_2, &features))
> 
> This too can be a separate patch, where we handle VCPU for Realms
> 
>>           return -EINVAL;
>> @@ -2312,6 +2325,7 @@ static const struct kvm_vcpu_ops
>> *arm64_vcpu_ops[] = {
>>       KVM_VCPU_OPS(VM_VHE, vhe_vcpu_ops),
>>       KVM_VCPU_OPS(VM_PKVM, pkvm_vcpu_ops),
>>       KVM_VCPU_OPS(VM_PROTECTED_PKVM, pkvm_vcpu_ops),
>> +    [VM_REALM] = NULL,
>>   };
>>     static void kvm_init_vcpu_ops(struct kvm_vcpu *vcpu)
>> @@ -3269,6 +3283,8 @@ static __init int kvm_arm_init(void)
>>         in_hyp_mode = is_kernel_in_hyp_mode();
>>   +    kvm_init_rmi();
>> +
>>       if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
>>           cpus_have_final_cap(ARM64_WORKAROUND_1508412))
>>           kvm_info("Guests without required CPU erratum workarounds
>> can deadlock system!\n" \
>> diff --git a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h b/arch/arm64/kvm/
>> hyp/include/nvhe/pkvm.h
>> index 0261b2bc681f..ae6ced6d7b9e 100644
>> --- a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
>> +++ b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
>> @@ -84,7 +84,7 @@ pkvm_hyp_vcpu_to_hyp_vm(struct pkvm_hyp_vcpu *hyp_vcpu)
>>     static inline bool pkvm_hyp_vcpu_is_protected(struct pkvm_hyp_vcpu
>> *hyp_vcpu)
>>   {
>> -    return vcpu_is_protected(&hyp_vcpu->vcpu);
>> +    return vcpu_is_protected_pkvm(&hyp_vcpu->vcpu);
>>   }
>>     static inline bool pkvm_hyp_vm_is_protected(struct pkvm_hyp_vm
>> *hyp_vm)
>> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/
>> nvhe/switch.c
>> index 89fb9dd351ad..6c03f48e6be3 100644
>> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
>> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
>> @@ -238,7 +238,7 @@ static const exit_handler_fn pvm_exit_handlers[] = {
>>     static const exit_handler_fn *kvm_get_exit_handler_array(struct
>> kvm_vcpu *vcpu)
>>   {
>> -    if (unlikely(vcpu_is_protected(vcpu)))
>> +    if (unlikely(vcpu_is_protected_pkvm(vcpu)))
>>           return pvm_exit_handlers;
>>         return hyp_exit_handlers;
>> @@ -259,7 +259,7 @@ static inline bool fixup_guest_exit(struct
>> kvm_vcpu *vcpu, u64 *exit_code)
>>        * it.  The check below is based on the one in
>>        * kvm_arch_vcpu_ioctl_run().
>>        */
>> -    if (unlikely(vcpu_is_protected(vcpu) && vcpu_mode_is_32bit(vcpu))) {
>> +    if (unlikely(vcpu_is_protected_pkvm(vcpu) &&
>> vcpu_mode_is_32bit(vcpu))) {
>>           /*
>>            * As we have caught the guest red-handed, decide that it isn't
>>            * fit for purpose anymore by making the vcpu invalid. The VMM
>> diff --git a/arch/arm64/kvm/hyp/nvhe/timer-sr.c b/arch/arm64/kvm/hyp/
>> nvhe/timer-sr.c
>> index 993065716913..17bd1ff621ab 100644
>> --- a/arch/arm64/kvm/hyp/nvhe/timer-sr.c
>> +++ b/arch/arm64/kvm/hyp/nvhe/timer-sr.c
>> @@ -48,7 +48,7 @@ void __timer_enable_traps(struct kvm_vcpu *vcpu)
>>        * or running a protected VM (we don't offset anything in this
>> case).
>>        */
>>       clr = CNTHCTL_EL1PCEN;
>> -    if (vcpu_is_protected(vcpu) ||
>> +    if (vcpu_is_protected_pkvm(vcpu) ||
>>           !timer_get_offset(vcpu_ptimer(vcpu)))
>>           set |= CNTHCTL_EL1PCTEN;
>>       else
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index 1db10d8d6db7..34ddcb2f094a 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -2814,17 +2814,17 @@ int kvm_arch_prepare_memory_region(struct kvm
>> *kvm,
>>       hva_t hva, reg_end;
>>       int ret = 0;
>>   -    if (kvm_vm_is_protected(kvm)) {
>> +    if (kvm_vm_is_protected(kvm) && new &&
>> +        (new->flags & (KVM_MEM_LOG_DIRTY_PAGES | KVM_MEM_READONLY)))
>> +        return -EPERM;
>> +
>> +    if (kvm->arch.vm_flavor == VM_PROTECTED_PKVM) {
>>           /* Cannot modify memslots once a pVM has run. */
>>           if (pkvm_hyp_vm_is_created(kvm) &&
>>               (change == KVM_MR_DELETE || change == KVM_MR_MOVE)) {
>>               return -EPERM;
>>           }
>>   -        if (new &&
>> -            new->flags & (KVM_MEM_LOG_DIRTY_PAGES | KVM_MEM_READONLY)) {
>> -            return -EPERM;
>> -        }
>>       }
> 
> May be the above could be a preparatory patch or add the changes common
> for Realm and pVM when we come to do the memslot for Realms ?

Ack

>>         if (change != KVM_MR_CREATE && change != KVM_MR_MOVE &&
>> @@ -3158,13 +3158,14 @@ static const struct kvm_vm_s2_ops
>> kvm_default_vm_s2_ops = {
>>   };
>>     #define KVM_VM_S2_OPS(flavor, ops)        \
>> -        [(flavor)] = &(ops)
>> +        [flavor] = &(ops)
> 
> Spurious, unwanted change. Please drop this ^^

Sorry about that - I actually spotted it before posting, then put the
wrong branch into "git format-patch" and didn't notice :( It is correct
in the git tree.

Thanks,
Steve

>>     static const struct kvm_vm_s2_ops *arm64_vm_s2_ops[] = {
>>       KVM_VM_S2_OPS(VM_VHE, kvm_default_vm_s2_ops),
>>       KVM_VM_S2_OPS(VM_NVHE, kvm_default_vm_s2_ops),
>>       KVM_VM_S2_OPS(VM_PKVM, pkvm_vm_s2_ops),
>>       KVM_VM_S2_OPS(VM_PROTECTED_PKVM, protected_pkvm_vm_s2_ops),
>> +    [VM_REALM] = NULL,
>>   };
>>     static int kvm_vm_init_vm_s2_ops(struct kvm *kvm)
>> diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
>> new file mode 100644
>> index 000000000000..5ecc8b349869
>> --- /dev/null
>> +++ b/arch/arm64/kvm/rmi.c
>> @@ -0,0 +1,18 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (C) 2023-2026 ARM Ltd.
>> + */
>> +
>> +#include <linux/kvm_host.h>
>> +
>> +#include <asm/virt.h>
>> +
>> +void kvm_init_rmi(void)
>> +{
>> +    if (kvm_get_mode() != KVM_MODE_RMM)
>> +        return;
> 
> Even this could be delayed to the end ? and this can be an empty stub
> for now.
>> +
>> +    /* TODO: Check if the RMI is available */
>> +
>> +    /* Future patch will enable static branch kvm_rmi_is_available */
> 
> Suzuki
>