Re: [PATCH v12 11/46] arm64: RMI: Activate realm on first VCPU run

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

On 02/03/2026 14:40, Marc Zyngier wrote:
> On Wed, 17 Dec 2025 10:10:48 +0000,
> Steven Price <steven.price@arm.com> wrote:
>>
>> When a VCPU migrates to another physical CPU check
> 
> To another physical CPU?
> 
> That's not what kvm_arch_vcpu_run_pid_change() tracks. It really is
> limited to a new PID being associated to the vpcu thread. Which is
> indeed the case when the vpcu runs for the first time, but that's
> about it.
> 
> If you need to track the physical CPU, we have some tracking for it in
> vcpu_load(), but that'd need some rework.

Sorry that was just a complete brainfart when I wrote that commit
message. We don't care about physical CPUs - this is just catching the
first VCPU run. Thanks for catching that.

>> if this is the first
>> time the guest has run, and if so activate the realm.
>>
>> Before the realm can be activated it must first be created, this is a
>> stub in this patch and will be filled in by a later patch.
>>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> ---
>> New patch for v12
>> ---
>>  arch/arm64/include/asm/kvm_rmi.h |  1 +
>>  arch/arm64/kvm/arm.c             |  6 +++++
>>  arch/arm64/kvm/rmi.c             | 42 ++++++++++++++++++++++++++++++++
>>  3 files changed, 49 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/kvm_rmi.h b/arch/arm64/include/asm/kvm_rmi.h
>> index cb7350f8a01a..e4534af06d96 100644
>> --- a/arch/arm64/include/asm/kvm_rmi.h
>> +++ b/arch/arm64/include/asm/kvm_rmi.h
>> @@ -69,6 +69,7 @@ void kvm_init_rmi(void);
>>  u32 kvm_realm_ipa_limit(void);
>>  
>>  int kvm_init_realm_vm(struct kvm *kvm);
>> +int kvm_activate_realm(struct kvm *kvm);
>>  void kvm_destroy_realm(struct kvm *kvm);
>>  void kvm_realm_destroy_rtts(struct kvm *kvm);
>>  
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index 941d1bec8e77..542df37b9e82 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -951,6 +951,12 @@ int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
>>  			return ret;
>>  	}
>>  
>> +	if (kvm_is_realm(vcpu->kvm)) {
>> +		ret = kvm_activate_realm(kvm);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>>  	mutex_lock(&kvm->arch.config_lock);
>>  	set_bit(KVM_ARCH_FLAG_HAS_RAN_ONCE, &kvm->arch.flags);
>>  	mutex_unlock(&kvm->arch.config_lock);
>> diff --git a/arch/arm64/kvm/rmi.c b/arch/arm64/kvm/rmi.c
>> index e57e8b7eafa9..98929382c365 100644
>> --- a/arch/arm64/kvm/rmi.c
>> +++ b/arch/arm64/kvm/rmi.c
>> @@ -223,6 +223,48 @@ void kvm_realm_destroy_rtts(struct kvm *kvm)
>>  	WARN_ON(realm_tear_down_rtt_range(realm, 0, (1UL << ia_bits)));
>>  }
>>  
>> +static int realm_ensure_created(struct kvm *kvm)
>> +{
>> +	/* Provided in later patch */
>> +	return -ENXIO;
>> +}
>> +
>> +int kvm_activate_realm(struct kvm *kvm)
>> +{
>> +	struct realm *realm = &kvm->arch.realm;
>> +	int ret;
>> +
>> +	if (!kvm_is_realm(kvm))
>> +		return -ENXIO;
> 
> nit: you already checked for this in caller.

Ack

>> +
>> +	if (kvm_realm_state(kvm) == REALM_STATE_ACTIVE)
>> +		return 0;
> 
> You probably also want to return early once the realm has been marked
> as dead -- it shouldn't be able to be a zombie and die twice.

Indeed, >= would be a better check.

Thanks,
Steve

>> +
>> +	guard(mutex)(&kvm->arch.config_lock);
>> +	/* Check again with the lock held */
>> +	if (kvm_realm_state(kvm) == REALM_STATE_ACTIVE)
>> +		return 0;
>> +
>> +	ret = realm_ensure_created(kvm);
>> +	if (ret)
>> +		return ret;
>> +
>> +	/* Mark state as dead in case we fail */
>> +	WRITE_ONCE(realm->state, REALM_STATE_DEAD);
>> +
>> +	if (!irqchip_in_kernel(kvm)) {
>> +		/* Userspace irqchip not yet supported with realms */
>> +		return -EOPNOTSUPP;
>> +	}
>> +
>> +	ret = rmi_realm_activate(virt_to_phys(realm->rd));
>> +	if (ret)
>> +		return -ENXIO;
>> +
>> +	WRITE_ONCE(realm->state, REALM_STATE_ACTIVE);
>> +	return 0;
>> +}
>> +
>>  void kvm_destroy_realm(struct kvm *kvm)
>>  {
>>  	struct realm *realm = &kvm->arch.realm;
> 
> Thanks,
> 
> 	M.
>