linux-kernel - Re: [PATCH v6 10/43] arm64: kvm: Allow passing machine type in KVM creation

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Message-ID: <a580d287-2fb0-4e9d-adbb-57e4dbf25765@redhat.com>
Date: Wed, 29 Jan 2025 14:07:51 +1000
From: Gavin Shan <gshan@...hat.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>,
 Suzuki K Poulose <suzuki.poulose@....com>, 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>,
 Shanker Donthineni <sdonthineni@...dia.com>, Alper Gun
 <alpergun@...gle.com>, "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>
Subject: Re: [PATCH v6 10/43] arm64: kvm: Allow passing machine type in KVM
 creation

On 12/13/24 1:55 AM, Steven Price wrote:
> Previously machine type was used purely for specifying the physical
> address size of the guest. Reserve the higher bits to specify an ARM
> specific machine type and declare a new type 'KVM_VM_TYPE_ARM_REALM'
> used to create a realm guest.
> 
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>   arch/arm64/kvm/arm.c     | 17 +++++++++++++++++
>   arch/arm64/kvm/mmu.c     |  3 ---
>   include/uapi/linux/kvm.h | 19 +++++++++++++++----
>   3 files changed, 32 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index c505ec61180a..73016e1e0067 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -207,6 +207,23 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>   	mutex_unlock(&kvm->lock);
>   #endif
>   
> +	if (type & ~(KVM_VM_TYPE_ARM_MASK | KVM_VM_TYPE_ARM_IPA_SIZE_MASK))
> +		return -EINVAL;
> +
> +	switch (type & KVM_VM_TYPE_ARM_MASK) {
> +	case KVM_VM_TYPE_ARM_NORMAL:
> +		break;
> +	case KVM_VM_TYPE_ARM_REALM:
> +		kvm->arch.is_realm = true;
> +		if (!kvm_is_realm(kvm)) {
> +			/* Realm support unavailable */
> +			return -EINVAL;
> +		}
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
>   	kvm_init_nested(kvm);
>   
>   	ret = kvm_share_hyp(kvm, kvm + 1);

Corresponding to comments for PATCH[6], the block of the code can be modified
to avoid using kvm_is_realm() here. In this way, kvm_is_realm() can be simplifed
as I commented for PATCH[6].

	case KVM_VM_TYPE_ARM_REALM:
		if (static_branch_unlikely(&kvm_rme_is_available))
			return -EPERM;	/* -EPERM may be more suitable than -EINVAL */

		kvm->arch.is_realm = true;
		break;

Thanks,
Gavin