cpuidle-haltpoll: disable host side polling when kvm virtualized

When performing guest side polling, it is not necessary to
also perform host side polling.

So disable host side polling, via the new MSR interface,
when loading cpuidle-haltpoll driver.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

arch/x86/Kconfig

@@ -794,6 +794,7 @@ config KVM_GUEST
 	bool "KVM Guest support (including kvmclock)"
 	depends on PARAVIRT
 	select PARAVIRT_CLOCK
+	select ARCH_CPUIDLE_HALTPOLL
 	default y
 	---help---
 	  This option enables various optimizations for running under the KVM
@@ -802,6 +803,12 @@ config KVM_GUEST
 	  underlying device model, the host provides the guest with
 	  timing infrastructure such as time of day, and system time
 
+config ARCH_CPUIDLE_HALTPOLL
+        def_bool n
+        prompt "Disable host haltpoll when loading haltpoll driver"
+        help
+	  If virtualized under KVM, disable host haltpoll.
+
 config PVH
 	bool "Support for running PVH guests"
 	---help---

arch/x86/include/asm/cpuidle_haltpoll.h

@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ARCH_HALTPOLL_H
+#define _ARCH_HALTPOLL_H
+
+void arch_haltpoll_enable(void);
+void arch_haltpoll_disable(void);
+
+#endif

arch/x86/kernel/kvm.c

@@ -875,3 +875,45 @@ void __init kvm_spinlock_init(void)
 }
 
 #endif	/* CONFIG_PARAVIRT_SPINLOCKS */
+
+#ifdef CONFIG_ARCH_CPUIDLE_HALTPOLL
+
+static void kvm_disable_host_haltpoll(void *i)
+{
+	wrmsrl(MSR_KVM_POLL_CONTROL, 0);
+}
+
+static void kvm_enable_host_haltpoll(void *i)
+{
+	wrmsrl(MSR_KVM_POLL_CONTROL, 1);
+}
+
+void arch_haltpoll_enable(void)
+{
+	if (!kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL)) {
+		printk(KERN_ERR "kvm: host does not support poll control\n");
+		printk(KERN_ERR "kvm: host upgrade recommended\n");
+		return;
+	}
+
+	preempt_disable();
+	/* Enable guest halt poll disables host halt poll */
+	kvm_disable_host_haltpoll(NULL);
+	smp_call_function(kvm_disable_host_haltpoll, NULL, 1);
+	preempt_enable();
+}
+EXPORT_SYMBOL_GPL(arch_haltpoll_enable);
+
+void arch_haltpoll_disable(void)
+{
+	if (!kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL))
+		return;
+
+	preempt_disable();
+	/* Enable guest halt poll disables host halt poll */
+	kvm_enable_host_haltpoll(NULL);
+	smp_call_function(kvm_enable_host_haltpoll, NULL, 1);
+	preempt_enable();
+}
+EXPORT_SYMBOL_GPL(arch_haltpoll_disable);
+#endif

drivers/cpuidle/cpuidle-haltpoll.c

@@ -15,6 +15,7 @@
 #include <linux/module.h>
 #include <linux/sched/idle.h>
 #include <linux/kvm_para.h>
+#include <linux/cpuidle_haltpoll.h>
 
 static int default_enter_idle(struct cpuidle_device *dev,
 			      struct cpuidle_driver *drv, int index)
@@ -47,6 +48,7 @@ static struct cpuidle_driver haltpoll_driver = {
 
 static int __init haltpoll_init(void)
 {
+	int ret;
 	struct cpuidle_driver *drv = &haltpoll_driver;
 
 	cpuidle_poll_state_init(drv);
@@ -54,11 +56,16 @@ static int __init haltpoll_init(void)
 	if (!kvm_para_available())
 		return 0;
 
-	return cpuidle_register(&haltpoll_driver, NULL);
+	ret = cpuidle_register(&haltpoll_driver, NULL);
+	if (ret == 0)
+		arch_haltpoll_enable();
+
+	return ret;
 }
 
 static void __exit haltpoll_exit(void)
 {
+	arch_haltpoll_disable();
 	cpuidle_unregister(&haltpoll_driver);
 }
 

include/linux/cpuidle_haltpoll.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _CPUIDLE_HALTPOLL_H
+#define _CPUIDLE_HALTPOLL_H
+
+#ifdef CONFIG_ARCH_CPUIDLE_HALTPOLL
+#include <asm/cpuidle_haltpoll.h>
+#else
+static inline void arch_haltpoll_enable(void)
+{
+}
+
+static inline void arch_haltpoll_disable(void)
+{
+}
+#endif
+#endif