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

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Message-ID: <f04bdf46-c752-43ec-88fa-dcd37f29d374@arm.com>
Date: Wed, 17 Dec 2025 14:29:46 +0000
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Steven Price <steven.price@....com>, kvm@...r.kernel.org,
 kvmarm@...ts.linux.dev
Cc: Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
 Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
 Oliver Upton <oliver.upton@...ux.dev>, Zenghui Yu <yuzenghui@...wei.com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Joey Gouly <joey.gouly@....com>, Alexandru Elisei
 <alexandru.elisei@....com>, Christoffer Dall <christoffer.dall@....com>,
 Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
 Gavin Shan <gshan@...hat.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 Alper Gun <alpergun@...gle.com>, "Aneesh Kumar K . V"
 <aneesh.kumar@...nel.org>, Emi Kisanuki <fj0570is@...itsu.com>,
 Vishal Annapurve <vannapurve@...gle.com>
Subject: Re: [PATCH v12 11/46] arm64: RMI: Activate realm on first VCPU run

On 17/12/2025 10:10, Steven Price wrote:
> When a VCPU migrates to another physical CPU check 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@....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;
> +
> +	if (kvm_realm_state(kvm) == REALM_STATE_ACTIVE)
> +		return 0;
> +
> +	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;
> +	}

super minor nit: We could do this check before create the realm, within
the config_lock'ed region.

Suzuki