UPSTREAM: <carry>: require configuration file enablement

similarly to what we do for the managed CPU (aka workload partitioning)
feature, introduce a master configuration file
`/etc/kubernetes/openshift-llc-alignment` which needs to be present for
the LLC alignment feature to be activated, in addition to the policy
option being required.

Note this replace the standard upstream feature gate check.

This can be dropped when the feature per  KEP
kubernetes/enhancements#4800 goes beta.

Signed-off-by: Francesco Romani <[email protected]>

Author: ffromani

pkg/kubelet/cm/cpumanager/policy_options.go

@@ -22,9 +22,11 @@ import (
 
 	"k8s.io/apimachinery/pkg/util/sets"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
+	"k8s.io/klog/v2"
 	kubefeatures "k8s.io/kubernetes/pkg/features"
 	"k8s.io/kubernetes/pkg/kubelet/cm/cpumanager/topology"
 	"k8s.io/kubernetes/pkg/kubelet/cm/topologymanager"
+	"k8s.io/kubernetes/pkg/kubelet/llcalign"
 )
 
 // Names of the options, as part of the user interface.
@@ -58,6 +60,14 @@ func CheckPolicyOptionAvailable(option string) error {
 		return fmt.Errorf("unknown CPU Manager Policy option: %q", option)
 	}
 
+	// must override the base feature gate check. Relevant only for alpha (disabled by default).
+	// for beta options are enabled by default and we totally want to keep the possibility to
+	// disable them explicitly.
+	if alphaOptions.Has(option) && checkPolicyOptionHasEnablementFile(option) {
+		// note that we override the decision and shortcut exit with success
+		// all other cases exit early with failure.
+		return nil
+	}
 	if alphaOptions.Has(option) && !utilfeature.DefaultFeatureGate.Enabled(kubefeatures.CPUManagerPolicyAlphaOptions) {
 		return fmt.Errorf("CPU Manager Policy Alpha-level Options not enabled, but option %q provided", option)
 	}
@@ -183,3 +193,13 @@ func ValidateStaticPolicyOptions(opts StaticPolicyOptions, topology *topology.CP
 	}
 	return nil
 }
+
+func checkPolicyOptionHasEnablementFile(option string) bool {
+	switch option {
+	case PreferAlignByUnCoreCacheOption:
+		val := llcalign.IsEnabled()
+		klog.InfoS("policy option enablement file check", "option", option, "enablementFile", val)
+		return val
+	}
+	return false
+}

pkg/kubelet/cm/cpumanager/policy_options_test.go

@@ -25,6 +25,7 @@ import (
 	pkgfeatures "k8s.io/kubernetes/pkg/features"
 	"k8s.io/kubernetes/pkg/kubelet/cm/cpumanager/topology"
 	"k8s.io/kubernetes/pkg/kubelet/cm/topologymanager"
+	"k8s.io/kubernetes/pkg/kubelet/llcalign"
 )
 
 type optionAvailTest struct {
@@ -258,3 +259,65 @@ func TestPolicyOptionsCompatibility(t *testing.T) {
 		})
 	}
 }
+
+func TestPolicyOptionsAvailableWithEnablement(t *testing.T) {
+
+	type optionAvailEnabTest struct {
+		name                  string
+		option                string
+		featureGate           featuregate.Feature
+		featureGateEnable     bool
+		featureEnablementFlag bool
+		expectedAvailable     bool
+	}
+
+	testCases := []optionAvailEnabTest{
+		{
+			name:                  "all disabled",
+			option:                PreferAlignByUnCoreCacheOption,
+			featureGate:           pkgfeatures.CPUManagerPolicyAlphaOptions,
+			featureGateEnable:     false, // expected standard case
+			featureEnablementFlag: false,
+			expectedAvailable:     false,
+		},
+		{
+			name:                  "all enabled",
+			option:                PreferAlignByUnCoreCacheOption,
+			featureGate:           pkgfeatures.CPUManagerPolicyAlphaOptions,
+			featureGateEnable:     true, // this should not be allowed by OCP profiles
+			featureEnablementFlag: true,
+			expectedAvailable:     true,
+		},
+		{
+			name:                  "enabled by feature gate",
+			option:                PreferAlignByUnCoreCacheOption,
+			featureGate:           pkgfeatures.CPUManagerPolicyAlphaOptions,
+			featureGateEnable:     true, // this should not be allowed by OCP profiles, makes no sense either
+			featureEnablementFlag: false,
+			expectedAvailable:     true,
+		},
+		{
+			name:                  "enabled by enablement file",
+			option:                PreferAlignByUnCoreCacheOption,
+			featureGate:           pkgfeatures.CPUManagerPolicyAlphaOptions,
+			featureGateEnable:     false,
+			featureEnablementFlag: true,
+			expectedAvailable:     true,
+		},
+	}
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, testCase.featureGate, testCase.featureGateEnable)
+			oldEnablementFlag := llcalign.TestOnlySetEnabled(testCase.featureEnablementFlag)
+
+			err := CheckPolicyOptionAvailable(testCase.option)
+
+			_ = llcalign.TestOnlySetEnabled(oldEnablementFlag)
+
+			isEnabled := (err == nil)
+			if isEnabled != testCase.expectedAvailable {
+				t.Errorf("option %q available got=%v expected=%v", testCase.option, isEnabled, testCase.expectedAvailable)
+			}
+		})
+	}
+}

pkg/kubelet/llcalign/llcalign.go

@@ -0,0 +1,46 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package llcalign
+
+import (
+	"os"
+)
+
+var (
+	llcAlignmentEnabled  bool
+	llcAlignmentFilename = "/etc/kubernetes/openshift-llc-alignment"
+)
+
+func init() {
+	readEnablementFile()
+}
+
+func readEnablementFile() {
+	if _, err := os.Stat(llcAlignmentFilename); err == nil {
+		llcAlignmentEnabled = true
+	}
+}
+
+func IsEnabled() bool {
+	return llcAlignmentEnabled
+}
+
+func TestOnlySetEnabled(enabled bool) bool {
+	oldEnabled := llcAlignmentEnabled
+	llcAlignmentEnabled = enabled
+	return oldEnabled
+}