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))
 );