kvm: x86: add trace event for pvclock updates

The new trace event records:
  * the id of vcpu being updated
  * the pvclock_vcpu_time_info struct being written to guest memory

This is useful for debugging pvclock bugs, such as the bug fixed by
"[PATCH] kvm: x86: Fix kvm clock versioning.".
Signed-off-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/trace.h

@@ -5,6 +5,7 @@
 #include <asm/vmx.h>
 #include <asm/svm.h>
 #include <asm/clocksource.h>
+#include <asm/pvclock-abi.h>
 
 #undef TRACE_SYSTEM
 #define TRACE_SYSTEM kvm
@@ -877,6 +878,42 @@ TRACE_EVENT(kvm_ple_window,
 #define trace_kvm_ple_window_shrink(vcpu_id, new, old) \
 	trace_kvm_ple_window(false, vcpu_id, new, old)
 
+TRACE_EVENT(kvm_pvclock_update,
+	TP_PROTO(unsigned int vcpu_id, struct pvclock_vcpu_time_info *pvclock),
+	TP_ARGS(vcpu_id, pvclock),
+
+	TP_STRUCT__entry(
+		__field(	unsigned int,	vcpu_id			)
+		__field(	__u32,		version			)
+		__field(	__u64,		tsc_timestamp		)
+		__field(	__u64,		system_time		)
+		__field(	__u32,		tsc_to_system_mul	)
+		__field(	__s8,		tsc_shift		)
+		__field(	__u8,		flags			)
+	),
+
+	TP_fast_assign(
+		__entry->vcpu_id	   = vcpu_id;
+		__entry->version	   = pvclock->version;
+		__entry->tsc_timestamp	   = pvclock->tsc_timestamp;
+		__entry->system_time	   = pvclock->system_time;
+		__entry->tsc_to_system_mul = pvclock->tsc_to_system_mul;
+		__entry->tsc_shift	   = pvclock->tsc_shift;
+		__entry->flags		   = pvclock->flags;
+	),
+
+	TP_printk("vcpu_id %u, pvclock { version %u, tsc_timestamp 0x%llx, "
+		  "system_time 0x%llx, tsc_to_system_mul 0x%x, tsc_shift %d, "
+		  "flags 0x%x }",
+		  __entry->vcpu_id,
+		  __entry->version,
+		  __entry->tsc_timestamp,
+		  __entry->system_time,
+		  __entry->tsc_to_system_mul,
+		  __entry->tsc_shift,
+		  __entry->flags)
+);
+
 #endif /* _TRACE_KVM_H */
 
 #undef TRACE_INCLUDE_PATH

arch/x86/kvm/x86.c

@@ -1661,6 +1661,8 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 
 	vcpu->hv_clock.flags = pvclock_flags;
 
+	trace_kvm_pvclock_update(v->vcpu_id, &vcpu->hv_clock);
+
 	kvm_write_guest_cached(v->kvm, &vcpu->pv_time,
 				&vcpu->hv_clock,
 				sizeof(vcpu->hv_clock));