replay: notify vCPU when BH is scheduled

vCPU execution should be suspended when new BH is scheduled.
This is needed to avoid guest timeouts caused by the long cycles
of the execution. In replay mode execution may hang when
vCPU sleeps and block event comes to the queue.
This patch adds notification which wakes up vCPU or interrupts
execution of guest code.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

--

v2: changed first_cpu to current_cpu (suggested by Richard Henderson)
v4: moved vCPU notification to aio_bh_enqueue (suggested by Paolo Bonzini)
Message-Id: <165364837317.688121.17680519919871405281.stgit@pasha-ThinkPad-X280>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/sysemu/cpu-timers.h

@@ -59,6 +59,7 @@ int64_t icount_round(int64_t count);
 /* if the CPUs are idle, start accounting real time to virtual clock. */
 void icount_start_warp_timer(void);
 void icount_account_warp_timer(void);
+void icount_notify_exit(void);
 
 /*
  * CPU Ticks and Clock

softmmu/icount.c

@@ -486,3 +486,11 @@ void icount_configure(QemuOpts *opts, Error **errp)
                    qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
                    NANOSECONDS_PER_SECOND / 10);
 }
+
+void icount_notify_exit(void)
+{
+    if (icount_enabled() && current_cpu) {
+        qemu_cpu_kick(current_cpu);
+        qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
+    }
+}

stubs/icount.c

@@ -43,3 +43,7 @@ void icount_account_warp_timer(void)
 {
     abort();
 }
+
+void icount_notify_exit(void)
+{
+}

util/async.c

@@ -33,6 +33,7 @@
 #include "block/raw-aio.h"
 #include "qemu/coroutine_int.h"
 #include "qemu/coroutine-tls.h"
+#include "sysemu/cpu-timers.h"
 #include "trace.h"
 
 /***********************************************************/
@@ -84,6 +85,13 @@ static void aio_bh_enqueue(QEMUBH *bh, unsigned new_flags)
     }
 
     aio_notify(ctx);
+    /*
+     * Workaround for record/replay.
+     * vCPU execution should be suspended when new BH is set.
+     * This is needed to avoid guest timeouts caused
+     * by the long cycles of the execution.
+     */
+    icount_notify_exit();
 }
 
 /* Only called from aio_bh_poll() and aio_ctx_finalize() */