[PATCH v2 02/17] KVM: arm64: nv: Allocate VNCR page when required

[Ganapatrao Kulkarni]

On 08-04-2025 04:22 pm, Marc Zyngier wrote:
> If running a NV guest on an ARMv8.4-NV capable system, let's
> allocate an additional page that will be used by the hypervisor
> to fulfill system register accesses.
> 
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>   arch/arm64/kvm/nested.c | 9 +++++++++
>   arch/arm64/kvm/reset.c  | 1 +
>   2 files changed, 10 insertions(+)
> 
> diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
> index 4a3fc11f7ecf3..884b3e25795c4 100644
> --- a/arch/arm64/kvm/nested.c
> +++ b/arch/arm64/kvm/nested.c
> @@ -55,6 +55,12 @@ int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu)
>   	    !cpus_have_final_cap(ARM64_HAS_HCR_NV1))
>   		return -EINVAL;
>   
> +	if (!vcpu->arch.ctxt.vncr_array)
> +		vcpu->arch.ctxt.vncr_array = (u64 *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
> +
> +	if (!vcpu->arch.ctxt.vncr_array)
> +		return -ENOMEM;
> +
>   	/*
>   	 * Let's treat memory allocation failures as benign: If we fail to
>   	 * allocate anything, return an error and keep the allocated array
> @@ -85,6 +91,9 @@ int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu)
>   		for (int i = kvm->arch.nested_mmus_size; i < num_mmus; i++)
>   			kvm_free_stage2_pgd(&kvm->arch.nested_mmus[i]);
>   
> +		free_page((unsigned long)vcpu->arch.ctxt.vncr_array);
> +		vcpu->arch.ctxt.vncr_array = NULL;
> +
>   		return ret;
>   	}
>   
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index f82fcc614e136..965e1429b9f6e 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -158,6 +158,7 @@ void kvm_arm_vcpu_destroy(struct kvm_vcpu *vcpu)
>   	if (sve_state)
>   		kvm_unshare_hyp(sve_state, sve_state + vcpu_sve_state_size(vcpu));
>   	kfree(sve_state);
> +	free_page((unsigned long)vcpu->arch.ctxt.vncr_array);
>   	kfree(vcpu->arch.ccsidr);
>   }
>   

Please feel free to add.
Reviewed-by: Ganapatrao Kulkarni <gankulkarni at os.amperecomputing.com>

-- 
Thanks,
Ganapat/GK