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>
diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
index 1d65268..fe5e00e 100644
--- a/arch/x86/kvm/trace.h
+++ b/arch/x86/kvm/trace.h
@@ -764,21 +764,54 @@
{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))
);