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())
+			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;
+
+		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);
-- 
2.50.1