Re: [PATCH v22 09/23] KVM: arm64: Prevent unsupported vcpu features for VM types

[Marc Zyngier]

On Mon, 05 Oct 2026 10:07:40 +0100,
Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:
> 
> Prevent unsupported VCPU features for the protected VCPUs. Realms and pVMs
> not support 32bit EL1 or NV yet. pKVM doesn't rely on the host vcpu
> features and it clears the unsupported features while hyp_vcpu is
> initialised. Block the features early in the vcpu init if we detect
> incompatible features.
> 
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> ---
>  arch/arm64/kvm/arm.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index f31d31fa27ad9..9c2ef7ca6a961 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -1668,11 +1668,12 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level,
>  	return -EINVAL;
>  }
>  
> -static unsigned long system_supported_vcpu_features(void)
> +static unsigned long system_supported_vcpu_features(struct kvm_vcpu *vcpu)
>  {
>  	unsigned long features = KVM_VCPU_VALID_FEATURES;
>  
> -	if (!cpus_have_final_cap(ARM64_HAS_32BIT_EL1))
> +	if (vcpu_is_protected(vcpu) ||
> +	    !cpus_have_final_cap(ARM64_HAS_32BIT_EL1))
>  		clear_bit(KVM_ARM_VCPU_EL1_32BIT, &features);
>

This looks a bit daft. Why don't you simply use different base feature
sets for the various backends? The nothing else need to change.

	M.

-- 
Jazz isn't dead. It just smells funny.