Re: [PATCH 3/6] KVM: PPC: Wire up KVM_PPC_GET_COMPAT_CAPS ioctl

[Harsh Prateek Bora <harshpb@linux.ibm.com>]

On 30/04/26 11:19 am, Amit Machhiwal wrote:
> Add handling for KVM_PPC_GET_COMPAT_CAPS in kvm_arch_vm_ioctl() and
> advertise support via KVM_CAP_PPC_COMPAT_CAPS.
> 
> The ioctl retrieves host CPU compatibility capabilities via a
> PowerPC-specific backend implementation when available. If the
> capability is not supported, the ioctl returns success with no
> capabilities set, allowing userspace to fall back gracefully.
> 
> Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>
> ---
>   arch/powerpc/include/asm/kvm_ppc.h |  1 +
>   arch/powerpc/kvm/powerpc.c         | 19 +++++++++++++++++++
>   2 files changed, 20 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
> index 0953f2daa466..cadfb839e836 100644
> --- a/arch/powerpc/include/asm/kvm_ppc.h
> +++ b/arch/powerpc/include/asm/kvm_ppc.h
> @@ -319,6 +319,7 @@ struct kvmppc_ops {
>   	bool (*hash_v3_possible)(void);
>   	int (*create_vm_debugfs)(struct kvm *kvm);
>   	int (*create_vcpu_debugfs)(struct kvm_vcpu *vcpu, struct dentry *debugfs_dentry);
> +	int (*get_compat_cpu_ver)(struct kvm_ppc_compat_caps *host_caps);
>   };
>   
>   extern struct kvmppc_ops *kvmppc_hv_ops;
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 00302399fc37..f35017d83d77 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -697,6 +697,12 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   			}
>   		}
>   		break;
> +#if defined(CONFIG_KVM_BOOK3S_HV_POSSIBLE)
> +	case KVM_CAP_PPC_COMPAT_CAPS:
> +		if (kvmhv_on_pseries())

What about PowerNV ?
Also, can't we just check if get_compat_cpu_ver is initialized and 
return accordingly ?

> +			r = 1;
> +		break;
> +#endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */
>   	default:
>   		r = 0;
>   		break;
> @@ -2463,6 +2469,19 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
>   		r = kvm->arch.kvm_ops->svm_off(kvm);
>   		break;
>   	}
> +	case KVM_PPC_GET_COMPAT_CAPS: {
> +		struct kvm_ppc_compat_caps host_caps;
> +
> +		memset(&host_caps, 0, sizeof(host_caps));
> +		if (!kvm->arch.kvm_ops->get_compat_cpu_ver)
> +			goto out;

I guess we want to init r = 0 before returning in this case.
Also prefer break over goto unless really needed.

> +
> +		r = kvm->arch.kvm_ops->get_compat_cpu_ver(&host_caps);
> +		if (!r && copy_to_user(argp, &host_caps,
> +				     sizeof(host_caps)))
> +			r = -EFAULT;
> +		break;
> +	}
>   	default: {
>   		struct kvm *kvm = filp->private_data;
>   		r = kvm->arch.kvm_ops->arch_vm_ioctl(filp, ioctl, arg);