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tcg: Do not elide memory barriers for !CF_PARALLEL in system mode

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The virtio devices require proper memory ordering between
the vcpus and the iothreads.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2021-02-18 16:47:35 +00:00
parent f6ff4923b9
commit c914d46d0a
1 changed files with 13 additions and 1 deletions
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14
tcg/tcg-op.c
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@ -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);
}
}