The virtio devices require proper memory ordering between
the vcpus and the iothreads.
Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
---
tcg/tcg-op.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/tcg/tcg-op.c b/tcg/tcg-op.c
index 70475773f4..76dc7d8dc5 100644
--- a/tcg/tcg-op.c
+++ b/tcg/tcg-op.c
@@ -97,9 +97,13 @@ void tcg_gen_op6(TCGOpcode opc, TCGArg a1, TCGArg a2, TCGArg
a3,
void tcg_gen_mb(TCGBar mb_type)
{
- if (tcg_ctx->tb_cflags & CF_PARALLEL) {
- tcg_gen_op1(INDEX_op_mb, mb_type);
- }
+ /*
+ * It is tempting to elide the barrier in a single-threaded context
+ * (i.e. !(tb_cflags & CF_PARALLEL)), 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.
+ */
+ tcg_gen_op1(INDEX_op_mb, mb_type);
}
/* 32 bit ops */
--
2.25.1
