[RFC PATCH v1 1/2] kvm: Implement guest_exit_last_time()

[Leonardo Bras <leobras@xxxxxxxxxx>]

Keep track of the last time a cpu ran guest_exit(), and provide a helper to
make this information available to other files.

Signed-off-by: Leonardo Bras <leobras@xxxxxxxxxx>
---
 include/linux/kvm_host.h | 13 +++++++++++++
 virt/kvm/kvm_main.c      |  3 +++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 48f31dcd318a..be90d83d631a 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -470,31 +470,44 @@ static __always_inline void guest_state_enter_irqoff(void)
 {
 	instrumentation_begin();
 	trace_hardirqs_on_prepare();
 	lockdep_hardirqs_on_prepare();
 	instrumentation_end();
 
 	guest_context_enter_irqoff();
 	lockdep_hardirqs_on(CALLER_ADDR0);
 }
 
+DECLARE_PER_CPU(unsigned long, kvm_last_guest_exit);
+
+/*
+ * Returns time (jiffies) for the last guest exit in current cpu
+ */
+static inline unsigned long guest_exit_last_time(void)
+{
+	return this_cpu_read(kvm_last_guest_exit);
+}
+
 /*
  * Exit guest context and exit an RCU extended quiescent state.
  *
  * Between guest_context_enter_irqoff() and guest_context_exit_irqoff() it is
  * unsafe to use any code which may directly or indirectly use RCU, tracing
  * (including IRQ flag tracing), or lockdep. All code in this period must be
  * non-instrumentable.
  */
 static __always_inline void guest_context_exit_irqoff(void)
 {
 	context_tracking_guest_exit();
+
+	/* Keeps track of last guest exit */
+	this_cpu_write(kvm_last_guest_exit, jiffies);
 }
 
 /*
  * Stop accounting time towards a guest.
  * Must be called after exiting guest context.
  */
 static __always_inline void guest_timing_exit_irqoff(void)
 {
 	instrumentation_begin();
 	/* Flush the guest cputime we spent on the guest */
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fb49c2a60200..732b1ab43ac9 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -103,20 +103,23 @@ EXPORT_SYMBOL_GPL(halt_poll_ns_shrink);
  */
 
 DEFINE_MUTEX(kvm_lock);
 LIST_HEAD(vm_list);
 
 static struct kmem_cache *kvm_vcpu_cache;
 
 static __read_mostly struct preempt_ops kvm_preempt_ops;
 static DEFINE_PER_CPU(struct kvm_vcpu *, kvm_running_vcpu);
 
+DEFINE_PER_CPU(unsigned long, kvm_last_guest_exit);
+EXPORT_SYMBOL_GPL(kvm_last_guest_exit);
+
 struct dentry *kvm_debugfs_dir;
 EXPORT_SYMBOL_GPL(kvm_debugfs_dir);
 
 static const struct file_operations stat_fops_per_vm;
 
 static long kvm_vcpu_ioctl(struct file *file, unsigned int ioctl,
 			   unsigned long arg);
 #ifdef CONFIG_KVM_COMPAT
 static long kvm_vcpu_compat_ioctl(struct file *file, unsigned int ioctl,
 				  unsigned long arg);
-- 
2.44.0