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

[Marc Zyngier <maz@kernel.org>]

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.

> 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.

> +
> +	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.

> +
> +	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.

-- 
Without deviation from the norm, progress is not possible.