Re: [PATCH v4 7/8] KVM: arm64: Check whether a VM IOCTL is allowed in pKVM

[Oliver Upton <oupton@kernel.org>]

Hi Fuad,

On Wed, Nov 12, 2025 at 09:20:50AM +0000, Fuad Tabba wrote:
> +/*
> + * Check whether the KVM VM IOCTL is allowed in pKVM.
> + *
> + * Certain features are allowed only for non-protected VMs in pKVM, which is why
> + * this takes the VM (kvm) as a parameter.
> + */
> +static inline bool kvm_pkvm_ioctl_allowed(struct kvm *kvm, unsigned int ioctl)
> +{
> +	switch (ioctl) {
> +	case KVM_CREATE_IRQCHIP:
> +		return kvm_pkvm_ext_allowed(kvm, KVM_CAP_IRQCHIP);
> +	case KVM_ARM_SET_DEVICE_ADDR:
> +		return kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_SET_DEVICE_ADDR);
> +	case KVM_ARM_MTE_COPY_TAGS:
> +		return kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_MTE);
> +	case KVM_ARM_SET_COUNTER_OFFSET:
> +		return kvm_pkvm_ext_allowed(kvm, KVM_CAP_COUNTER_OFFSET);
> +	case KVM_HAS_DEVICE_ATTR:
> +	case KVM_SET_DEVICE_ATTR:
> +	case KVM_GET_DEVICE_ATTR:
> +		return kvm_pkvm_ext_allowed(kvm, KVM_CAP_DEVICE_CTRL) ||
> +		       kvm_pkvm_ext_allowed(kvm, KVM_CAP_VM_ATTRIBUTES);
> +	case KVM_ARM_GET_REG_WRITABLE_MASKS:
> +		return kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_SUPPORTED_REG_MASK_RANGES);
> +	default:
> +		return true;
> +	}
> +}
> +

I was thinking of something a bit more tabular since CCA will impose its
own restrictions + pKVM could share the ioctl <=> KVM_CAP association.

Anyway, ioctl filtering should be an allowlist (default to false) just
like kvm_pkvm_ext_allowed(). The default assumption is that new UAPI is not
supported for pVMs unless explicitly stated otherwise.

Thanks,
Oliver