Add a cpuidle driver that calls the architecture default_idle routine.

To be used in conjunction with the haltpoll governor.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

---
 arch/x86/kernel/process.c          |    2 -
 drivers/cpuidle/Kconfig            |    9 +++++
 drivers/cpuidle/Makefile           |    1 
 drivers/cpuidle/cpuidle-haltpoll.c |   65 +++++++++++++++++++++++++++++++++++++
 4 files changed, 76 insertions(+), 1 deletion(-)

Index: linux-2.6-newcpuidle.git/arch/x86/kernel/process.c
===================================================================
--- linux-2.6-newcpuidle.git.orig/arch/x86/kernel/process.c
+++ linux-2.6-newcpuidle.git/arch/x86/kernel/process.c
@@ -580,7 +580,7 @@ void __cpuidle default_idle(void)
 	safe_halt();
 	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
 }
-#ifdef CONFIG_APM_MODULE
+#if defined(CONFIG_APM_MODULE) || defined(CONFIG_HALTPOLL_CPUIDLE_MODULE)
 EXPORT_SYMBOL(default_idle);
 #endif
 
Index: linux-2.6-newcpuidle.git/drivers/cpuidle/Kconfig
===================================================================
--- linux-2.6-newcpuidle.git.orig/drivers/cpuidle/Kconfig
+++ linux-2.6-newcpuidle.git/drivers/cpuidle/Kconfig
@@ -51,6 +51,15 @@ depends on PPC
 source "drivers/cpuidle/Kconfig.powerpc"
 endmenu
 
+config HALTPOLL_CPUIDLE
+       tristate "Halt poll cpuidle driver"
+       depends on X86 && KVM_GUEST
+       default y
+       help
+         This option enables halt poll cpuidle driver, which allows to poll
+         before halting in the guest (more efficient than polling in the
+         host via halt_poll_ns for some scenarios).
+
 endif
 
 config ARCH_NEEDS_CPU_IDLE_COUPLED
Index: linux-2.6-newcpuidle.git/drivers/cpuidle/Makefile
===================================================================
--- linux-2.6-newcpuidle.git.orig/drivers/cpuidle/Makefile
+++ linux-2.6-newcpuidle.git/drivers/cpuidle/Makefile
@@ -7,6 +7,7 @@ obj-y += cpuidle.o driver.o governor.o s
 obj-$(CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED) += coupled.o
 obj-$(CONFIG_DT_IDLE_STATES)		  += dt_idle_states.o
 obj-$(CONFIG_ARCH_HAS_CPU_RELAX)	  += poll_state.o
+obj-$(CONFIG_HALTPOLL_CPUIDLE)		  += cpuidle-haltpoll.o
 
 ##################################################################################
 # ARM SoC drivers
Index: linux-2.6-newcpuidle.git/drivers/cpuidle/cpuidle-haltpoll.c
===================================================================
--- /dev/null
+++ linux-2.6-newcpuidle.git/drivers/cpuidle/cpuidle-haltpoll.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * cpuidle driver for haltpoll governor.
+ *
+ * Copyright 2019 Red Hat, Inc. and/or its affiliates.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ * Authors: Marcelo Tosatti <mtosatti@redhat.com>
+ */
+
+#include <linux/init.h>
+#include <linux/cpuidle.h>
+#include <linux/module.h>
+#include <linux/sched/idle.h>
+#include <linux/kvm_para.h>
+
+static int default_enter_idle(struct cpuidle_device *dev,
+			      struct cpuidle_driver *drv, int index)
+{
+	if (current_clr_polling_and_test()) {
+		local_irq_enable();
+		return index;
+	}
+	default_idle();
+	return index;
+}
+
+static struct cpuidle_driver haltpoll_driver = {
+	.name = "haltpoll",
+	.owner = THIS_MODULE,
+	.states = {
+		{ /* entry 0 is for polling */ },
+		{
+			.enter			= default_enter_idle,
+			.exit_latency		= 1,
+			.target_residency	= 1,
+			.power_usage		= -1,
+			.name			= "haltpoll idle",
+			.desc			= "default architecture idle",
+		},
+	},
+	.safe_state_index = 0,
+	.state_count = 2,
+};
+
+static int __init haltpoll_init(void)
+{
+	struct cpuidle_driver *drv = &haltpoll_driver;
+
+	cpuidle_poll_state_init(drv);
+
+	if (!kvm_para_available())
+		return 0;
+
+	return cpuidle_register(&haltpoll_driver, NULL);
+}
+
+static void __exit haltpoll_exit(void)
+{
+	cpuidle_unregister(&haltpoll_driver);
+}
+
+module_init(haltpoll_init);
+module_exit(haltpoll_exit);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Marcelo Tosatti <mtosatti@redhat.com>");
+