[Qemu-devel] [PATCH v7 3/7] trace: [tcg] Delay changes to dynamic state when translating

[Lluís Vilanova]

This keeps consistency across all decisions taken during translation
when the dynamic state of a vCPU is changed in the middle of translating
some guest code.

Signed-off-by: Lluís Vilanova <vilan...@ac.upc.edu>
---
 include/qom/cpu.h      |    3 +++
 qom/cpu.c              |    2 ++
 trace/control-target.c |   21 ++++++++++++++++++---
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 3f79a8e955..31c3e6018d 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -295,6 +295,8 @@ struct qemu_work_item;
  * @kvm_fd: vCPU file descriptor for KVM.
  * @work_mutex: Lock to prevent multiple access to queued_work_*.
  * @queued_work_first: First asynchronous work pending.
+ * @trace_dstate_delayed: Delayed changes to trace_dstate (includes all changes
+ *                        to @trace_dstate).
  * @trace_dstate: Dynamic tracing state of events for this vCPU (bitmask).
  *
  * State of one CPU core or thread.
@@ -370,6 +372,7 @@ struct CPUState {
      * Dynamically allocated based on bitmap requried to hold up to
      * trace_get_vcpu_event_count() entries.
      */
+    unsigned long *trace_dstate_delayed;
     unsigned long *trace_dstate;
 
     /* TODO Move common fields from CPUArchState here. */
diff --git a/qom/cpu.c b/qom/cpu.c
index 03d9190f8c..8e981ac6c7 100644
--- a/qom/cpu.c
+++ b/qom/cpu.c
@@ -367,6 +367,7 @@ static void cpu_common_initfn(Object *obj)
     QTAILQ_INIT(&cpu->breakpoints);
     QTAILQ_INIT(&cpu->watchpoints);
 
+    cpu->trace_dstate_delayed = bitmap_new(trace_get_vcpu_event_count());
     cpu->trace_dstate = bitmap_new(trace_get_vcpu_event_count());
 
     cpu_exec_initfn(cpu);
@@ -375,6 +376,7 @@ static void cpu_common_initfn(Object *obj)
 static void cpu_common_finalize(Object *obj)
 {
     CPUState *cpu = CPU(obj);
+    g_free(cpu->trace_dstate_delayed);
     g_free(cpu->trace_dstate);
 }
 
diff --git a/trace/control-target.c b/trace/control-target.c
index 7ebf6e0bcb..dba3b21bb0 100644
--- a/trace/control-target.c
+++ b/trace/control-target.c
@@ -1,13 +1,14 @@
 /*
  * Interface for configuring and controlling the state of tracing events.
  *
- * Copyright (C) 2014-2016 Lluís Vilanova <vilan...@ac.upc.edu>
+ * Copyright (C) 2014-2017 Lluís Vilanova <vilan...@ac.upc.edu>
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  * See the COPYING file in the top-level directory.
  */
 
 #include "qemu/osdep.h"
+#include "qom/cpu.h"
 #include "cpu.h"
 #include "trace.h"
 #include "trace/control.h"
@@ -57,6 +58,13 @@ void trace_event_set_state_dynamic(TraceEvent *ev, bool 
state)
     }
 }
 
+static void trace_event_synchronize_vcpu_state_dynamic(
+    CPUState *vcpu, run_on_cpu_data ignored)
+{
+    bitmap_copy(vcpu->trace_dstate, vcpu->trace_dstate_delayed,
+                trace_get_vcpu_event_count());
+}
+
 void trace_event_set_vcpu_state_dynamic(CPUState *vcpu,
                                         TraceEvent *ev, bool state)
 {
@@ -69,13 +77,20 @@ void trace_event_set_vcpu_state_dynamic(CPUState *vcpu,
     if (state_pre != state) {
         if (state) {
             trace_events_enabled_count++;
-            set_bit(vcpu_id, vcpu->trace_dstate);
+            set_bit(vcpu_id, vcpu->trace_dstate_delayed);
             (*ev->dstate)++;
         } else {
             trace_events_enabled_count--;
-            clear_bit(vcpu_id, vcpu->trace_dstate);
+            clear_bit(vcpu_id, vcpu->trace_dstate_delayed);
             (*ev->dstate)--;
         }
+        /*
+         * Delay changes until next TB; we want all TBs to be built from a
+         * single set of dstate values to ensure consistency of generated
+         * tracing code.
+         */
+        async_run_on_cpu(vcpu, trace_event_synchronize_vcpu_state_dynamic,
+                         RUN_ON_CPU_NULL);
     }
 }