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

[Harsh Prateek Bora]

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 <amach...@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);