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

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

On 11/11/2026 10:14, Suzuki K Poulose wrote:
> On 11/11/2026 10:11, Steven Price wrote:
>> On 10/11/2026 11:42, Kohei Enju wrote:
>>> Hi Steve,
>>
>> Hi Kohei,
>>
>>> On 11/02 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.
>>>>   - Also adjust the memslot preparation checks to reflect the changes.
>>>>
>>>> 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))
>>>> +
>>>>   #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));        \
>>>>       })
>>>
>>> I've tested the integration branch and found that the secondary CPU
>>> bring-up fails:
>>>      [    1.426502] smp: Bringing up secondary CPUs ...
>>>      [    9.194442] CPU1: failed to come online
>>>      [    9.194558] CPU1: failed in unknown state : 0x0
>>>      [    9.197714] smp: Brought up 1 node, 1 CPU
>>>      [    9.197775] SMP: Total of 1 processors activated.
>>>
>>> It seems that this patch missed replacing a use of
>>> vcpu_is_protected() introduced by the following commit:
>>>
>>>      25d726dddc23 ("KVM: arm64: Reject host power-on of a vCPU that
>>> EL2 holds powered off")
>>>
>>> The following diff fixes the issue for me. Also, though not included in
>>> the diff, I think vcpu_is_protected() in __pkvm_create_hyp_vcpu() should
>>> be replaced with vcpu_is_protected_pkvm() as well.
>>
>> Thanks for the patch - I'll include that in v2.
> 
> Please could we make it something like this :
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 4edcaf1090f9..2108c1bf5481 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -989,7 +989,8 @@ static bool kvm_arm_vcpu_suspended(struct kvm_vcpu
> *vcpu)
>  /* Only the guest's CPU_ON may start a vCPU EL2 holds powered off. */
>  bool kvm_pkvm_vcpu_is_powered_off(struct kvm_vcpu *vcpu)
>  {
> -       return READ_ONCE(vcpu->arch.mp_state.mp_state) ==
> KVM_MP_STATE_UNINITIALIZED;
> +       return vcpu_is_protected_pkvm(vcpu) &&
> +               READ_ONCE(vcpu->arch.mp_state.mp_state) ==
> KVM_MP_STATE_UNINITIALIZED;
>  }

This part looks good.

>  int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
> diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
> index b01f8d44033f..b7606c3542f8 100644
> --- a/arch/arm64/kvm/psci.c
> +++ b/arch/arm64/kvm/psci.c
> @@ -68,7 +68,7 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu
> *source_vcpu)
>          * STOPPED before that is the VMM's pause.
>          */
>         if (!kvm_arm_vcpu_stopped(vcpu) ||
> -           (vcpu_is_protected(vcpu) && !
> kvm_pkvm_vcpu_is_powered_off(vcpu))) {
> +           !kvm_pkvm_vcpu_is_powered_off(vcpu)) {
>                 if (kvm_psci_version(source_vcpu) != KVM_ARM_PSCI_0_1)
>                         ret = PSCI_RET_ALREADY_ON;
>                 else

I think this is broken. kvm_pkvm_vcpu_is_powered_off() is defined as:

bool kvm_pkvm_vcpu_is_powered_off(struct kvm_vcpu *vcpu)
{
	return vcpu_is_protected_pkvm(vcpu) &&
		READ_ONCE(vcpu->arch.mp_state.mp_state) == KVM_MP_STATE_UNINITIALIZED;
}

So if !vcpu_is_protected_pkvm() then it's always false, so this would
break non-pKVM VMs.

Thanks,
Steve

> 
> i.e, check for pkvm vcpu as it should have been in the first case,
> rather than spilling the check for protected vcpu and an explicit
> check to see if that is powered off ?
> 
> 
> Suzuki>
>> Thanks,
>> Steve
>>
>>> Thanks,
>>> Kohei
>>>
>>> ---8<---
>>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>>> index 522a837637fe..be676c13e219 100644
>>> --- a/arch/arm64/kvm/arm.c
>>> +++ b/arch/arm64/kvm/arm.c
>>> @@ -960,7 +960,8 @@ static void __kvm_arm_vcpu_power_off(struct
>>> kvm_vcpu *vcpu, u32 mp_state)
>>>   /* The guest's own CPU_OFF: EL2 has already powered the vCPU off. */
>>>   void kvm_arm_vcpu_power_off(struct kvm_vcpu *vcpu)
>>>   {
>>> -       u32 mp_state = vcpu_is_protected(vcpu) ?
>>> KVM_MP_STATE_UNINITIALIZED : KVM_MP_STATE_STOPPED;
>>> +       u32 mp_state = vcpu_is_protected_pkvm(vcpu) ?
>>> +                      KVM_MP_STATE_UNINITIALIZED :
>>> KVM_MP_STATE_STOPPED;
>>>
>>>          spin_lock(&vcpu->arch.mp_state_lock);
>>>          __kvm_arm_vcpu_power_off(vcpu, mp_state);
>>> diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
>>> index b01f8d44033f..6674e8d6ff4c 100644
>>> --- a/arch/arm64/kvm/psci.c
>>> +++ b/arch/arm64/kvm/psci.c
>>> @@ -68,7 +68,7 @@ static unsigned long kvm_psci_vcpu_on(struct
>>> kvm_vcpu *source_vcpu)
>>>           * STOPPED before that is the VMM's pause.
>>>           */
>>>          if (!kvm_arm_vcpu_stopped(vcpu) ||
>>> -           (vcpu_is_protected(vcpu) && !
>>> kvm_pkvm_vcpu_is_powered_off(vcpu))) {
>>> +           (vcpu_is_protected_pkvm(vcpu) && !
>>> kvm_pkvm_vcpu_is_powered_off(vcpu))) {
>>>                  if (kvm_psci_version(source_vcpu) != KVM_ARM_PSCI_0_1)
>>>                          ret = PSCI_RET_ALREADY_ON;
>>>                  else
>>>
>>
>