sched/vtime: Move guest enter/exit vtime accounting to separate helpers

Provide separate helpers for guest enter/exit vtime accounting instead of
open coding the logic within the context tracking code.  This will allow
KVM x86 to handle vtime accounting slightly differently when using tick-
based accounting.

Opportunstically delete the vtime_account_kernel() stub now that all
callers are wrapped with CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=y.

No functional change intended.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>

include/linux/context_tracking.h

@@ -102,16 +102,12 @@ 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)
 {
 	instrumentation_begin();
-	if (vtime_accounting_enabled_this_cpu())
-		vtime_guest_enter(current);
-	else
-		current->flags |= PF_VCPU;
+	vtime_account_guest_enter();
 	instrumentation_end();
 
 	if (context_tracking_enabled())
@@ -137,10 +133,7 @@ static __always_inline void guest_exit_irqoff(void)
 		__context_tracking_exit(CONTEXT_GUEST);
 
 	instrumentation_begin();
-	if (vtime_accounting_enabled_this_cpu())
-		vtime_guest_exit(current);
-	else
-		current->flags &= ~PF_VCPU;
+	vtime_account_guest_exit();
 	instrumentation_end();
 }
 
@@ -153,8 +146,7 @@ static __always_inline void guest_enter_irqoff(void)
 	 * to flush.
 	 */
 	instrumentation_begin();
-	vtime_account_kernel(current);
-	current->flags |= PF_VCPU;
+	vtime_account_guest_enter();
 	rcu_virt_note_context_switch(smp_processor_id());
 	instrumentation_end();
 }
@@ -163,8 +155,7 @@ static __always_inline void guest_exit_irqoff(void)
 {
 	instrumentation_begin();
 	/* Flush the guest cputime we spent on the guest */
-	vtime_account_kernel(current);
-	current->flags &= ~PF_VCPU;
+	vtime_account_guest_exit();
 	instrumentation_end();
 }
 #endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */

include/linux/vtime.h

@@ -3,6 +3,8 @@
 #define _LINUX_KERNEL_VTIME_H
 
 #include <linux/context_tracking_state.h>
+#include <linux/sched.h>
+
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
 #include <asm/vtime.h>
 #endif
@@ -18,6 +20,17 @@ struct task_struct;
 static inline bool vtime_accounting_enabled_this_cpu(void) { return true; }
 extern void vtime_task_switch(struct task_struct *prev);
 
+static __always_inline void vtime_account_guest_enter(void)
+{
+	vtime_account_kernel(current);
+	current->flags |= PF_VCPU;
+}
+
+static __always_inline void vtime_account_guest_exit(void)
+{
+
+}
+
 #elif defined(CONFIG_VIRT_CPU_ACCOUNTING_GEN)
 
 /*
@@ -49,12 +62,38 @@ static inline void vtime_task_switch(struct task_struct *prev)
 		vtime_task_switch_generic(prev);
 }
 
+static __always_inline void vtime_account_guest_enter(void)
+{
+	if (vtime_accounting_enabled_this_cpu())
+		vtime_guest_enter(current);
+	else
+		current->flags |= PF_VCPU;
+}
+
+static __always_inline void vtime_account_guest_exit(void)
+{
+	if (vtime_accounting_enabled_this_cpu())
+		vtime_guest_exit(current);
+	else
+		current->flags &= ~PF_VCPU;
+}
+
+
 #else /* !CONFIG_VIRT_CPU_ACCOUNTING */
 
-static inline bool vtime_accounting_enabled_cpu(int cpu) {return false; }
 static inline bool vtime_accounting_enabled_this_cpu(void) { return false; }
 static inline void vtime_task_switch(struct task_struct *prev) { }
 
+static __always_inline void vtime_account_guest_enter(void)
+{
+	current->flags |= PF_VCPU;
+}
+
+static __always_inline void vtime_account_guest_exit(void)
+{
+	current->flags &= ~PF_VCPU;
+}
+
 #endif
 
 /*
@@ -63,9 +102,7 @@ static inline void vtime_task_switch(struct task_struct *prev) { }
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
 extern void vtime_account_kernel(struct task_struct *tsk);
 extern void vtime_account_idle(struct task_struct *tsk);
-#else /* !CONFIG_VIRT_CPU_ACCOUNTING */
-static inline void vtime_account_kernel(struct task_struct *tsk) { }
-#endif /* !CONFIG_VIRT_CPU_ACCOUNTING */
+#endif /* CONFIG_VIRT_CPU_ACCOUNTING */
 
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
 extern void arch_vtime_task_switch(struct task_struct *tsk);