context_tracking: Consolidate guest enter/exit wrappers

Consolidate the guest enter/exit wrappers by providing stubs for the
context tracking helpers as necessary.  This will allow moving the
wrappers under KVM without having to bleed too many #ifdefs into the
soon-to-be KVM code.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>

include/linux/context_tracking.h

@@ -76,18 +76,7 @@ static __always_inline void context_tracking_guest_enter_irqoff(void)
 	if (context_tracking_enabled())
 		__context_tracking_enter(CONTEXT_GUEST);
 
-	/* KVM does not hold any references to rcu protected data when it
-	 * switches CPU into a guest mode. In fact switching to a guest mode
-	 * is very similar to exiting to userspace from rcu point of view. In
-	 * addition CPU may stay in a guest mode for quite a long time (up to
-	 * one time slice). Lets treat guest mode as quiescent state, just like
-	 * we do with user-mode execution.
-	 */
-	if (!context_tracking_enabled_this_cpu()) {
-		instrumentation_begin();
-		rcu_virt_note_context_switch(smp_processor_id());
-		instrumentation_end();
-	}
+	return context_tracking_enabled_this_cpu();
 }
 
 static __always_inline void context_tracking_guest_exit_irqoff(void)
@@ -116,6 +105,17 @@ static inline void user_exit_irqoff(void) { }
 static inline enum ctx_state exception_enter(void) { return 0; }
 static inline void exception_exit(enum ctx_state prev_ctx) { }
 static inline enum ctx_state ct_state(void) { return CONTEXT_DISABLED; }
+
+static __always_inline bool context_tracking_guest_enter_irqoff(void)
+{
+	return false;
+}
+
+static __always_inline void context_tracking_guest_exit_irqoff(void)
+{
+
+}
+
 #endif /* !CONFIG_CONTEXT_TRACKING */
 
 #define CT_WARN_ON(cond) WARN_ON(context_tracking_enabled() && (cond))
@@ -126,48 +126,41 @@ extern void context_tracking_init(void);
 static inline void context_tracking_init(void) { }
 #endif /* CONFIG_CONTEXT_TRACKING_FORCE */
 
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
 /* must be called with irqs disabled */
 static __always_inline void guest_enter_irqoff(void)
 {
+	/*
+	 * This is running in ioctl context so its safe to assume that it's the
+	 * stime pending cputime to flush.
+	 */
 	instrumentation_begin();
 	vtime_account_guest_enter();
 	instrumentation_end();
 
-	context_tracking_guest_enter_irqoff();
-}
-
-static __always_inline void guest_exit_irqoff(void)
-{
-	context_tracking_guest_exit_irqoff();
-
-	instrumentation_begin();
-	vtime_account_guest_exit();
-	instrumentation_end();
-}
-
-#else
-static __always_inline void guest_enter_irqoff(void)
-{
 	/*
-	 * This is running in ioctl context so its safe
-	 * to assume that it's the stime pending cputime
-	 * to flush.
+	 * KVM does not hold any references to rcu protected data when it
+	 * switches CPU into a guest mode. In fact switching to a guest mode
+	 * is very similar to exiting to userspace from rcu point of view. In
+	 * addition CPU may stay in a guest mode for quite a long time (up to
+	 * one time slice). Lets treat guest mode as quiescent state, just like
+	 * we do with user-mode execution.
 	 */
-	instrumentation_begin();
-	vtime_account_guest_enter();
-	rcu_virt_note_context_switch(smp_processor_id());
-	instrumentation_end();
+	if (!context_tracking_guest_enter_irqoff()) {
+		instrumentation_begin();
+		rcu_virt_note_context_switch(smp_processor_id());
+		instrumentation_end();
+	}
 }
 
 static __always_inline void guest_exit_irqoff(void)
 {
+	context_tracking_guest_exit_irqoff();
+
 	instrumentation_begin();
 	/* Flush the guest cputime we spent on the guest */
 	vtime_account_guest_exit();
 	instrumentation_end();
 }
-#endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */
 
 static inline void guest_exit(void)
 {