[patch 5/5] cpuidle-haltpoll: disable host side polling when kvm virtualized

[Marcelo Tosatti <mtosatti@redhat.com>]

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>

---
 arch/x86/Kconfig                        |    7 +++++
 arch/x86/include/asm/cpuidle_haltpoll.h |    8 ++++++
 arch/x86/kernel/kvm.c                   |   42 ++++++++++++++++++++++++++++++++
 drivers/cpuidle/cpuidle-haltpoll.c      |   10 ++++++-
 include/linux/cpuidle_haltpoll.h        |   16 ++++++++++++
 5 files changed, 82 insertions(+), 1 deletion(-)

Index: linux-2.6.git/arch/x86/include/asm/cpuidle_haltpoll.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.git/arch/x86/include/asm/cpuidle_haltpoll.h	2019-06-13 18:42:06.891491238 -0400
@@ -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
Index: linux-2.6.git/drivers/cpuidle/cpuidle-haltpoll.c
===================================================================
--- linux-2.6.git.orig/drivers/cpuidle/cpuidle-haltpoll.c	2019-06-13 18:41:39.305933413 -0400
+++ linux-2.6.git/drivers/cpuidle/cpuidle-haltpoll.c	2019-06-13 18:42:06.892491222 -0400
@@ -14,6 +14,7 @@
 #include <linux/cpuidle.h>
 #include <linux/module.h>
 #include <linux/sched/idle.h>
+#include <linux/cpuidle_haltpoll.h>
 
 static int default_enter_idle(struct cpuidle_device *dev,
 			      struct cpuidle_driver *drv, int index)
@@ -46,15 +47,22 @@
 
 static int __init haltpoll_init(void)
 {
+	int ret;
 	struct cpuidle_driver *drv = &haltpoll_driver;
 
 	cpuidle_poll_state_init(drv);
 
-	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);
 }
 
Index: linux-2.6.git/include/linux/cpuidle_haltpoll.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.git/include/linux/cpuidle_haltpoll.h	2019-06-13 18:42:06.892491222 -0400
@@ -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
Index: linux-2.6.git/arch/x86/Kconfig
===================================================================
--- linux-2.6.git.orig/arch/x86/Kconfig	2019-06-13 18:41:39.305933413 -0400
+++ linux-2.6.git/arch/x86/Kconfig	2019-06-13 18:42:06.893491206 -0400
@@ -787,6 +787,7 @@
 	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
@@ -795,6 +796,12 @@
 	  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---
Index: linux-2.6.git/arch/x86/kernel/kvm.c
===================================================================
--- linux-2.6.git.orig/arch/x86/kernel/kvm.c	2019-06-13 18:41:39.305933413 -0400
+++ linux-2.6.git/arch/x86/kernel/kvm.c	2019-06-13 18:42:06.893491206 -0400
@@ -853,3 +853,45 @@
 }
 
 #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