linux-kernel - Re: [PATCH v8 21/43] KVM: arm64: Handle realm VCPU load

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Message-ID: <9a09a3fe-c91c-457f-b6da-9fccbf98e649@arm.com>
Date: Mon, 19 May 2025 18:48:54 +0100
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>
Subject: Re: [PATCH v8 21/43] KVM: arm64: Handle realm VCPU load

On 16/04/2025 14:41, Steven Price wrote:
> When loading a realm VCPU much of the work is handled by the RMM so only
> some of the actions are required. Rearrange kvm_arch_vcpu_load()
> slightly so we can bail out early for a realm guest.
> 
> Signed-off-by: Steven Price <steven.price@....com>
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> ---
>   arch/arm64/kvm/arm.c | 13 +++++++++----
>   1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index cf707130ef66..08d5e0d76749 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -644,10 +644,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)

I think we use the pkvm hook to skip to the nommu goto, to avoid
the VMID allocation and context flush.

>   	kvm_timer_vcpu_load(vcpu);
>   	kvm_vgic_load(vcpu);
>   	kvm_vcpu_load_debug(vcpu);
> -	if (has_vhe())
> -		kvm_vcpu_load_vhe(vcpu);
> -	kvm_arch_vcpu_load_fp(vcpu);
> -	kvm_vcpu_pmu_restore_guest(vcpu);
>   	if (kvm_arm_is_pvtime_enabled(&vcpu->arch))
>   		kvm_make_request(KVM_REQ_RECORD_STEAL, vcpu);

We could also move thise pvtime to the bottom too ?

>   
> @@ -671,6 +667,15 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>   			     &vcpu->arch.vgic_cpu.vgic_v3);
>   	}
>   
> +	/* No additional state needs to be loaded on Realmed VMs */
> +	if (vcpu_is_rec(vcpu))
> +		return;
> +
> +	if (has_vhe())
> +		kvm_vcpu_load_vhe(vcpu);
> +	kvm_arch_vcpu_load_fp(vcpu);
> +	kvm_vcpu_pmu_restore_guest(vcpu);
> +

With the above addressed:

Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>

>   	if (!cpumask_test_cpu(cpu, vcpu->kvm->arch.supported_cpus))
>   		vcpu_set_on_unsupported_cpu(vcpu);
>   }