Re: [PATCH v12 27/46] KVM: arm64: Handle Realm PSCI requests

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 02/03/2026 16:39, Marc Zyngier wrote:
> On Wed, 17 Dec 2025 10:11:04 +0000,
> Steven Price <steven.price@arm.com> wrote:
>>
>> The RMM needs to be informed of the target REC when a PSCI call is made
>> with an MPIDR argument. Expose an ioctl to the userspace in case the PSCI
>> is handled by it.
>>
>> Co-developed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> Reviewed-by: Gavin Shan <gshan@redhat.com>
>> ---
>> Changes since v11:
>>   * RMM->RMI renaming.
>> Changes since v6:
>>   * Use vcpu_is_rec() rather than kvm_is_realm(vcpu->kvm).
>>   * Minor renaming/formatting fixes.
>> ---
>>   arch/arm64/include/asm/kvm_rmi.h |  3 +++
>>   arch/arm64/kvm/arm.c             | 25 +++++++++++++++++++++++++
>>   arch/arm64/kvm/psci.c            | 30 ++++++++++++++++++++++++++++++
>>   arch/arm64/kvm/rmi.c             | 14 ++++++++++++++
>>   4 files changed, 72 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/kvm_rmi.h b/arch/arm64/include/asm/kvm_rmi.h
>> index bfe6428eaf16..77da297ca09d 100644
>> --- a/arch/arm64/include/asm/kvm_rmi.h
>> +++ b/arch/arm64/include/asm/kvm_rmi.h
>> @@ -118,6 +118,9 @@ int realm_map_non_secure(struct realm *realm,
>>   			 kvm_pfn_t pfn,
>>   			 unsigned long size,
>>   			 struct kvm_mmu_memory_cache *memcache);
>> +int realm_psci_complete(struct kvm_vcpu *source,
>> +			struct kvm_vcpu *target,
>> +			unsigned long status);
>>   
>>   static inline bool kvm_realm_is_private_address(struct realm *realm,
>>   						unsigned long addr)
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index 06070bc47ee3..fb04d032504e 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -1797,6 +1797,22 @@ static int kvm_arm_vcpu_set_events(struct kvm_vcpu *vcpu,
>>   	return __kvm_arm_vcpu_set_events(vcpu, events);
>>   }
>>   
>> +static int kvm_arm_vcpu_rmi_psci_complete(struct kvm_vcpu *vcpu,
>> +					  struct kvm_arm_rmi_psci_complete *arg)
>> +{
>> +	struct kvm_vcpu *target = kvm_mpidr_to_vcpu(vcpu->kvm, arg->target_mpidr);
>> +
>> +	if (!target)
>> +		return -EINVAL;
>> +
>> +	/*
>> +	 * RMM v1.0 only supports PSCI_RET_SUCCESS or PSCI_RET_DENIED
>> +	 * for the status. But, let us leave it to the RMM to filter
>> +	 * for making this future proof.
>> +	 */
>> +	return realm_psci_complete(vcpu, target, arg->psci_status);
>> +}
>> +
>>   long kvm_arch_vcpu_ioctl(struct file *filp,
>>   			 unsigned int ioctl, unsigned long arg)
>>   {
>> @@ -1925,6 +1941,15 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>>   
>>   		return kvm_arm_vcpu_finalize(vcpu, what);
>>   	}
>> +	case KVM_ARM_VCPU_RMI_PSCI_COMPLETE: {
>> +		struct kvm_arm_rmi_psci_complete req;
>> +
>> +		if (!vcpu_is_rec(vcpu))
>> +			return -EPERM;
> 
> Same remark as for the other ioctl: EPERM is not quite describing the
> problem.
> 
>> +		if (copy_from_user(&req, argp, sizeof(req)))
>> +			return -EFAULT;
>> +		return kvm_arm_vcpu_rmi_psci_complete(vcpu, &req);
>> +	}
>>   	default:
>>   		r = -EINVAL;
>>   	}
>> diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
>> index 3b5dbe9a0a0e..a68f3c1878a5 100644
>> --- a/arch/arm64/kvm/psci.c
>> +++ b/arch/arm64/kvm/psci.c
>> @@ -103,6 +103,12 @@ static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu)
>>   
>>   	reset_state->reset = true;
>>   	kvm_make_request(KVM_REQ_VCPU_RESET, vcpu);
>> +	/*
>> +	 * Make sure we issue PSCI_COMPLETE before the VCPU can be
>> +	 * scheduled.
>> +	 */
>> +	if (vcpu_is_rec(vcpu))
>> +		realm_psci_complete(source_vcpu, vcpu, PSCI_RET_SUCCESS);
>>
> 
> I really think in-kernel PSCI should be for NS VMs only. The whole
> reason for moving to userspace support was to stop adding features to
> an already complex infrastructure, and CCA is exactly the sort of
> things we want userspace to deal with.

Agreed. How would you like us to enforce this ? Should we always exit
to the VMM, even if it hasn't requested the handling ? (I guess it is
fine and in the worst case VMM could exit, it being buggy)

Cheers
Suzuki


> 
> Thanks,
> 
> 	M.
>