cpuidle: Implement BPF extensible cpuidle class

The BPF cpuidle ext governor registers at postcore_initcall()
but remains disabled by default due to its low priority "rating" (1).
Activation requires adjust higer "rating" than other governors within BPF.

Core Components:
1.**struct cpuidle_gov_ext_ops** – BPF-overridable operations:
- ops.enable()/ops.disable(): enable or disable callback
- ops.select(): cpu Idle-state selection logic
- ops.set_stop_tick(): Scheduler tick management after state selection
- ops.reflect(): feedback info about previous idle state.
- ops.init()/ops.deinit(): Initialization or cleanup.

2.**Critical kfuncs for kernel state access**:
- bpf_cpuidle_ext_gov_update_rating():
  Activate ext governor by raising rating must be called from "ops.init()"
- bpf_cpuidle_ext_gov_latency_req(): get idle-state latency constraints
- bpf_tick_nohz_get_sleep_length(): get CPU sleep duration in tickless mode

Signed-off-by: Lin Yikai <[email protected]>

Author: Lin Yikai

drivers/cpuidle/Kconfig

@@ -44,6 +44,18 @@ config CPU_IDLE_GOV_HALTPOLL
 
 	  Some virtualized workloads benefit from using it.
 
+config CPU_IDLE_GOV_EXT
+    bool "bpf cpuidle ext governor"
+	depends on BPF_SYSCALL && BPF_JIT && DEBUG_INFO_BTF
+	default y
+	help
+	  This governor implements a simple cpuidle ext governor,
+	  which can be customized by a BPF program without modifying
+	  kernel code.
+
+	  Some scenarios benefit where CPUidle policy needs
+	  to be customized based on user-space requirements.
+
 config DT_IDLE_STATES
 	bool
 

drivers/cpuidle/governors/Makefile

@@ -7,3 +7,4 @@ obj-$(CONFIG_CPU_IDLE_GOV_LADDER) += ladder.o
 obj-$(CONFIG_CPU_IDLE_GOV_MENU) += menu.o
 obj-$(CONFIG_CPU_IDLE_GOV_TEO) += teo.o
 obj-$(CONFIG_CPU_IDLE_GOV_HALTPOLL) += haltpoll.o
+obj-$(CONFIG_CPU_IDLE_GOV_EXT) += ext.o