accel: use store_release/load_acquire for cross-thread exit_request

Reads and writes cpu->exit_request do not use a load-acquire/store-release
pair right now, but this means that cpu_exit() may not write cpu->exit_request
after any flags that are read by the vCPU thread.

Probably everything is protected one way or the other by the BQL, because
cpu->exit_request leads to the slow path, where the CPU thread often takes
the BQL (for example, to go to sleep by waiting on the BQL-protected
cpu->halt_cond); but it's not clear, so use load-acquire/store-release
consistently.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/hw/core/cpu-common.c b/hw/core/cpu-common.c
index 152abc9024..42463e6258 100644
--- a/hw/core/cpu-common.c
+++ b/hw/core/cpu-common.c
@@ -74,7 +74,8 @@ void cpu_reset_interrupt(CPUState *cpu, int mask)
 
 void cpu_exit(CPUState *cpu)
 {
-    qatomic_set(&cpu->exit_request, 1);
+    /* Ensure cpu_exec will see the reason why the exit request was set.  */
+    qatomic_store_release(&cpu->exit_request, true);
     /* Ensure cpu_exec will see the exit request after TCG has exited.  */
     smp_wmb();
     qatomic_set(&cpu->neg.icount_decr.u16.high, -1);