Re: [PATCH v17 06/20] KVM: arm64: CCA: Add a new mode for supporting Realm guests

[Kohei Enju <enju.kohei@fujitsu.com>]

Hi Suzuki,

On 09/08 17:22, Suzuki K Poulose wrote:
> Add an explicit mode to support Arm CCA guests.
> 
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 3 +++
>  arch/arm64/include/asm/kvm_host.h               | 1 +
>  arch/arm64/kvm/arm.c                            | 5 +++++
>  3 files changed, 9 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 68647ff4bdd24..1afe3df3b923e 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3256,6 +3256,9 @@ Kernel parameters
>  			nested: VHE-based mode with support for nested
>  				virtualization. Requires at least ARMv8.4
>  				hardware (with FEAT_NV2).
> +			rmm: Support for running confidential guests in Realm
> +			     world using RMM, as defined by Arm Confidential
> +			     Compute Architecture (CCA)
>  
>  			Defaults to VHE/nVHE based on hardware support. Setting
>  			mode to "protected" will disable kexec and hibernation
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index b2e99c5cb1cd3..31ae9d8d8e92f 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -69,6 +69,7 @@ enum kvm_mode {
>  	KVM_MODE_DEFAULT,
>  	KVM_MODE_PROTECTED,
>  	KVM_MODE_NV,
> +	KVM_MODE_RMM,
>  	KVM_MODE_NONE,
>  };
>  #ifdef CONFIG_KVM
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 9af3bbb2f8c24..50f0adfadab38 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -3264,6 +3264,11 @@ static int __init early_kvm_mode_cfg(char *arg)
>  		return 0;
>  	}
>  
> +	if (strcmp(arg, "rmm") == 0 && !WARN_ON(!is_kernel_in_hyp_mode())) {
> +		kvm_mode = KVM_MODE_RMM;
> +		return 0;
> +	}

Does this make NV support and CCA Realm VM support mutually exclusive?

Until the v16 series, we could run Realm VMs with:
  'kvm-arm.mode=nested'

As far as the AArch64 architecture is concerned, there does not seem to
be a reason to make them mutually exclusive. I am therefore wondering
whether this restriction is intentional.

Thanks,
Kohei

> +
>  	return -EINVAL;
>  }
>  early_param("kvm-arm.mode", early_kvm_mode_cfg);
> -- 
> 2.43.0
>