Merge branch 'timers-nohz-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull NOHZ changes from Ingo Molnar:
 "This tree adds full dynticks support to KVM guests (support the
  disabling of the timer tick on the guest).  The main missing piece was
  the recognition of guest execution as RCU extended quiescent state and
  related changes"

* 'timers-nohz-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  kvm,rcu,nohz: use RCU extended quiescent state when running KVM guest
  context_tracking: Export context_tracking_user_enter/exit
  context_tracking: Run vtime_user_enter/exit only when state == CONTEXT_USER
  context_tracking: Add stub context_tracking_is_enabled
  context_tracking: Generalize context tracking APIs to support user and guest
  context_tracking: Rename context symbols to prepare for transition state
  ppc: Remove unused cpp symbols in kvm headers

arch/powerpc/include/asm/kvm_book3s.h

@@ -106,10 +106,6 @@ struct kvmppc_vcpu_book3s {
 	spinlock_t mmu_lock;
 };
 
-#define CONTEXT_HOST		0
-#define CONTEXT_GUEST		1
-#define CONTEXT_GUEST_END	2
-
 #define VSID_REAL	0x07ffffffffc00000ULL
 #define VSID_BAT	0x07ffffffffb00000ULL
 #define VSID_64K	0x0800000000000000ULL

arch/x86/kernel/traps.c

@@ -123,7 +123,7 @@ enum ctx_state ist_enter(struct pt_regs *regs)
 		 * but we need to notify RCU.
 		 */
 		rcu_nmi_enter();
-		prev_state = IN_KERNEL;  /* the value is irrelevant. */
+		prev_state = CONTEXT_KERNEL;  /* the value is irrelevant. */
 	}
 
 	/*

include/linux/context_tracking.h

@@ -10,6 +10,8 @@
 #ifdef CONFIG_CONTEXT_TRACKING
 extern void context_tracking_cpu_set(int cpu);
 
+extern void context_tracking_enter(enum ctx_state state);
+extern void context_tracking_exit(enum ctx_state state);
 extern void context_tracking_user_enter(void);
 extern void context_tracking_user_exit(void);
 extern void __context_tracking_task_switch(struct task_struct *prev,
@@ -35,7 +37,8 @@ static inline enum ctx_state exception_enter(void)
 		return 0;
 
 	prev_ctx = this_cpu_read(context_tracking.state);
-	context_tracking_user_exit();
+	if (prev_ctx != CONTEXT_KERNEL)
+		context_tracking_exit(prev_ctx);
 
 	return prev_ctx;
 }
@@ -43,8 +46,8 @@ static inline enum ctx_state exception_enter(void)
 static inline void exception_exit(enum ctx_state prev_ctx)
 {
 	if (context_tracking_is_enabled()) {
-		if (prev_ctx == IN_USER)
-			context_tracking_user_enter();
+		if (prev_ctx != CONTEXT_KERNEL)
+			context_tracking_enter(prev_ctx);
 	}
 }
 
@@ -78,10 +81,16 @@ static inline void guest_enter(void)
 		vtime_guest_enter(current);
 	else
 		current->flags |= PF_VCPU;
+
+	if (context_tracking_is_enabled())
+		context_tracking_enter(CONTEXT_GUEST);
 }
 
 static inline void guest_exit(void)
 {
+	if (context_tracking_is_enabled())
+		context_tracking_exit(CONTEXT_GUEST);
+
 	if (vtime_accounting_enabled())
 		vtime_guest_exit(current);
 	else

include/linux/context_tracking_state.h

@@ -13,8 +13,9 @@ struct context_tracking {
 	 */
 	bool active;
 	enum ctx_state {
-		IN_KERNEL = 0,
-		IN_USER,
+		CONTEXT_KERNEL = 0,
+		CONTEXT_USER,
+		CONTEXT_GUEST,
 	} state;
 };
 
@@ -34,11 +35,13 @@ static inline bool context_tracking_cpu_is_enabled(void)
 
 static inline bool context_tracking_in_user(void)
 {
-	return __this_cpu_read(context_tracking.state) == IN_USER;
+	return __this_cpu_read(context_tracking.state) == CONTEXT_USER;
 }
 #else
 static inline bool context_tracking_in_user(void) { return false; }
 static inline bool context_tracking_active(void) { return false; }
+static inline bool context_tracking_is_enabled(void) { return false; }
+static inline bool context_tracking_cpu_is_enabled(void) { return false; }
 #endif /* CONFIG_CONTEXT_TRACKING */
 
 #endif

include/linux/kvm_host.h

@@ -779,7 +779,8 @@ static inline void kvm_guest_enter(void)
 	 * one time slice). Lets treat guest mode as quiescent state, just like
 	 * we do with user-mode execution.
 	 */
-	rcu_virt_note_context_switch(smp_processor_id());
+	if (!context_tracking_cpu_is_enabled())
+		rcu_virt_note_context_switch(smp_processor_id());
 }
 
 static inline void kvm_guest_exit(void)

kernel/context_tracking.c

@@ -39,15 +39,15 @@ void context_tracking_cpu_set(int cpu)
 }
 
 /**
- * context_tracking_user_enter - Inform the context tracking that the CPU is going to
- *                               enter userspace mode.
+ * context_tracking_enter - Inform the context tracking that the CPU is going
+ *                          enter user or guest space mode.
  *
  * This function must be called right before we switch from the kernel
- * to userspace, when it's guaranteed the remaining kernel instructions
- * to execute won't use any RCU read side critical section because this
- * function sets RCU in extended quiescent state.
+ * to user or guest space, when it's guaranteed the remaining kernel
+ * instructions to execute won't use any RCU read side critical section
+ * because this function sets RCU in extended quiescent state.
  */
-void context_tracking_user_enter(void)
+void context_tracking_enter(enum ctx_state state)
 {
 	unsigned long flags;
 
@@ -75,9 +75,8 @@ void context_tracking_user_enter(void)
 	WARN_ON_ONCE(!current->mm);
 
 	local_irq_save(flags);
-	if ( __this_cpu_read(context_tracking.state) != IN_USER) {
+	if ( __this_cpu_read(context_tracking.state) != state) {
 		if (__this_cpu_read(context_tracking.active)) {
-			trace_user_enter(0);
 			/*
 			 * At this stage, only low level arch entry code remains and
 			 * then we'll run in userspace. We can assume there won't be
@@ -85,7 +84,10 @@ void context_tracking_user_enter(void)
 			 * user_exit() or rcu_irq_enter(). Let's remove RCU's dependency
 			 * on the tick.
 			 */
-			vtime_user_enter(current);
+			if (state == CONTEXT_USER) {
+				trace_user_enter(0);
+				vtime_user_enter(current);
+			}
 			rcu_user_enter();
 		}
 		/*
@@ -101,24 +103,32 @@ void context_tracking_user_enter(void)
 		 * OTOH we can spare the calls to vtime and RCU when context_tracking.active
 		 * is false because we know that CPU is not tickless.
 		 */
-		__this_cpu_write(context_tracking.state, IN_USER);
+		__this_cpu_write(context_tracking.state, state);
 	}
 	local_irq_restore(flags);
 }
+NOKPROBE_SYMBOL(context_tracking_enter);
+EXPORT_SYMBOL_GPL(context_tracking_enter);
+
+void context_tracking_user_enter(void)
+{
+	context_tracking_enter(CONTEXT_USER);
+}
 NOKPROBE_SYMBOL(context_tracking_user_enter);
 
 /**
- * context_tracking_user_exit - Inform the context tracking that the CPU is
- *                              exiting userspace mode and entering the kernel.
+ * context_tracking_exit - Inform the context tracking that the CPU is
+ *                         exiting user or guest mode and entering the kernel.
  *
- * This function must be called after we entered the kernel from userspace
- * before any use of RCU read side critical section. This potentially include
- * any high level kernel code like syscalls, exceptions, signal handling, etc...
+ * This function must be called after we entered the kernel from user or
+ * guest space before any use of RCU read side critical section. This
+ * potentially include any high level kernel code like syscalls, exceptions,
+ * signal handling, etc...
  *
  * This call supports re-entrancy. This way it can be called from any exception
  * handler without needing to know if we came from userspace or not.
  */
-void context_tracking_user_exit(void)
+void context_tracking_exit(enum ctx_state state)
 {
 	unsigned long flags;
 
@@ -129,20 +139,29 @@ void context_tracking_user_exit(void)
 		return;
 
 	local_irq_save(flags);
-	if (__this_cpu_read(context_tracking.state) == IN_USER) {
+	if (__this_cpu_read(context_tracking.state) == state) {
 		if (__this_cpu_read(context_tracking.active)) {
 			/*
 			 * We are going to run code that may use RCU. Inform
 			 * RCU core about that (ie: we may need the tick again).
 			 */
 			rcu_user_exit();
-			vtime_user_exit(current);
-			trace_user_exit(0);
+			if (state == CONTEXT_USER) {
+				vtime_user_exit(current);
+				trace_user_exit(0);
+			}
 		}
-		__this_cpu_write(context_tracking.state, IN_KERNEL);
+		__this_cpu_write(context_tracking.state, CONTEXT_KERNEL);
 	}
 	local_irq_restore(flags);
 }
+NOKPROBE_SYMBOL(context_tracking_exit);
+EXPORT_SYMBOL_GPL(context_tracking_exit);
+
+void context_tracking_user_exit(void)
+{
+	context_tracking_exit(CONTEXT_USER);
+}
 NOKPROBE_SYMBOL(context_tracking_user_exit);
 
 /**

kernel/sched/core.c

@@ -2853,7 +2853,7 @@ asmlinkage __visible void __sched schedule_user(void)
 	 * we find a better solution.
 	 *
 	 * NB: There are buggy callers of this function.  Ideally we
-	 * should warn if prev_state != IN_USER, but that will trigger
+	 * should warn if prev_state != CONTEXT_USER, but that will trigger
 	 * too frequently to make sense yet.
 	 */
 	enum ctx_state prev_state = exception_enter();