KVM: x86: require matched TSC offsets for master clock

With master clock, a pvclock clock read calculates:

ret = system_timestamp + [ (rdtsc + tsc_offset) - tsc_timestamp ]

Where 'rdtsc' is the host TSC.

system_timestamp and tsc_timestamp are unique, one tuple
per VM: the "master clock".

Given a host with synchronized TSCs, its obvious that
guest TSC must be matched for the above to guarantee monotonicity.

Allow master clock usage only if guest TSCs are synchronized.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 36 insertions, 3 deletions

diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
index 1d6526856080..fe5e00ed7036 100644
--- a/arch/x86/kvm/trace.h
+++ b/arch/x86/kvm/trace.h
@@ -764,21 +764,54 @@ TRACE_EVENT(
 	{VCLOCK_HPET, "hpet"}				\
 
 TRACE_EVENT(kvm_update_master_clock,
-	TP_PROTO(bool use_master_clock, unsigned int host_clock),
-	TP_ARGS(use_master_clock, host_clock),
+	TP_PROTO(bool use_master_clock, unsigned int host_clock, bool offset_matched),
+	TP_ARGS(use_master_clock, host_clock, offset_matched),
 
 	TP_STRUCT__entry(
 		__field(		bool,	use_master_clock	)
 		__field(	unsigned int,	host_clock		)
+		__field(		bool,	offset_matched		)
 	),
 
 	TP_fast_assign(
 		__entry->use_master_clock	= use_master_clock;
 		__entry->host_clock		= host_clock;
+		__entry->offset_matched		= offset_matched;
 	),
 
-	TP_printk("masterclock %d hostclock %s",
+	TP_printk("masterclock %d hostclock %s offsetmatched %u",
 		  __entry->use_master_clock,
+		  __print_symbolic(__entry->host_clock, host_clocks),
+		  __entry->offset_matched)
+);
+
+TRACE_EVENT(kvm_track_tsc,
+	TP_PROTO(unsigned int vcpu_id, unsigned int nr_matched,
+		 unsigned int online_vcpus, bool use_master_clock,
+		 unsigned int host_clock),
+	TP_ARGS(vcpu_id, nr_matched, online_vcpus, use_master_clock,
+		host_clock),
+
+	TP_STRUCT__entry(
+		__field(	unsigned int,	vcpu_id			)
+		__field(	unsigned int,	nr_vcpus_matched_tsc	)
+		__field(	unsigned int,	online_vcpus		)
+		__field(	bool,		use_master_clock	)
+		__field(	unsigned int,	host_clock		)
+	),
+
+	TP_fast_assign(
+		__entry->vcpu_id		= vcpu_id;
+		__entry->nr_vcpus_matched_tsc	= nr_matched;
+		__entry->online_vcpus		= online_vcpus;
+		__entry->use_master_clock	= use_master_clock;
+		__entry->host_clock		= host_clock;
+	),
+
+	TP_printk("vcpu_id %u masterclock %u offsetmatched %u nr_online %u"
+		  " hostclock %s",
+		  __entry->vcpu_id, __entry->use_master_clock,
+		  __entry->nr_vcpus_matched_tsc, __entry->online_vcpus,
 		  __print_symbolic(__entry->host_clock, host_clocks))
 );