fallback to checking if config is in correct format

config/legacyconfig/migrate.go

@@ -43,6 +43,9 @@ func migrateK8sAndEKS(oldValues string, newConfig *config.Config) error {
 	oldConfig := &LegacyK8s{}
 	err := oldConfig.UnmarshalYAMLStrict([]byte(oldValues))
 	if err != nil {
+		if err := errIfConfigIsAlreadyConverted(oldValues); err != nil {
+			return err
+		}
 		return fmt.Errorf("unmarshal legacy config: %w", err)
 	}
 
@@ -91,6 +94,9 @@ func migrateK3sAndK0s(distro, oldValues string, newConfig *config.Config) error
 	oldConfig := &LegacyK0sAndK3s{}
 	err := oldConfig.UnmarshalYAMLStrict([]byte(oldValues))
 	if err != nil {
+		if err := errIfConfigIsAlreadyConverted(oldValues); err != nil {
+			return err
+		}
 		return fmt.Errorf("unmarshal legacy config: %w", err)
 	}
 
@@ -136,6 +142,14 @@ func migrateK3sAndK0s(distro, oldValues string, newConfig *config.Config) error
 	return convertBaseValues(oldConfig.BaseHelm, newConfig)
 }
 
+func errIfConfigIsAlreadyConverted(oldValues string) error {
+	currentConfig := &config.Config{}
+	if err := currentConfig.UnmarshalYAMLStrict([]byte(oldValues)); err == nil {
+		return fmt.Errorf("config is already in correct format")
+	}
+	return nil
+}
+
 func convertEtcd(oldConfig EtcdValues, newConfig *config.Config) error {
 	if oldConfig.Disabled {
 		newConfig.ControlPlane.BackingStore.Etcd.Deploy.StatefulSet.Enabled = false

config/legacyconfig/migrate_test.go

@@ -445,6 +445,50 @@ policies:
       podManagementPolicy: OrderedReady`,
 			ExpectedErr: "",
 		},
+		{
+			Name:   "k3s already migrated to correct format",
+			Distro: "k3s",
+			In: `sync:
+  fromHost:
+    nodes:
+      enabled: false
+  toHost:
+    serviceAccounts:
+      enabled: false
+controlPlane:
+  distro:
+    k3s:
+      enabled: true
+      image:
+        tag: v1.30.2-k3s2
+  statefulSet:
+    scheduling:
+      podManagementPolicy: OrderedReady
+
+`,
+			ExpectedErr: "migrate legacy k3s values: config is already in correct format",
+		},
+		{
+			Name:   "k8s already migrated to correct format",
+			Distro: "k8s",
+			In: `sync:
+  fromHost:
+    nodes:
+      enabled: false
+  toHost:
+    serviceAccounts:
+      enabled: false
+controlPlane:
+  distro:
+    k8s:
+      enabled: true
+  statefulSet:
+    scheduling:
+      podManagementPolicy: OrderedReady
+
+`,
+			ExpectedErr: "migrate legacy k8s values: config is already in correct format",
+		},
 	}
 
 	for _, testCase := range testCases {