@@ -102,7 +102,19 @@ void tcg_gen_br(TCGLabel *l)
void tcg_gen_mb(TCGBar mb_type)
{
- if (tcg_ctx->gen_tb->cflags & CF_PARALLEL) {
+#ifdef CONFIG_USER_ONLY
+ bool parallel = tcg_ctx->gen_tb->cflags & CF_PARALLEL;
+#else
+ /*
+ * It is tempting to elide the barrier in a uniprocessor context.
+ * However, even with a single cpu we have i/o threads running in
+ * parallel, and lack of memory order can result in e.g. virtio
+ * queue entries being read incorrectly.
+ */
+ bool parallel = true;
+#endif
+
+ if (parallel) {
tcg_gen_op1(INDEX_op_mb, mb_type);
}
}
The virtio devices require proper memory ordering between the vcpus and the iothreads. Signed-off-by: Richard Henderson <richard.henderson@linaro.org> --- tcg/tcg-op.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)