Re: [Qemu-devel] [PATCH v2 10/45] translate-all: guarantee that tb_hash only holds valid TBs

[Richard Henderson]

On 07/16/2017 10:03 AM, Emilio G. Cota wrote:
> @@ -1073,13 +1073,17 @@ void tb_phys_invalidate(TranslationBlock *tb, 
> tb_page_addr_t page_addr)
>   
>       assert_tb_locked();
>   
> -    atomic_set(&tb->invalid, true);
> -
>       /* remove the TB from the hash list */
>       phys_pc = tb->page_addr[0] + (tb->pc & ~TARGET_PAGE_MASK);
>       h = tb_hash_func(phys_pc, tb->pc, tb->flags, tb->trace_vcpu_dstate);
>       qht_remove(&tcg_ctx.tb_ctx.htable, tb, h);
>   
> +    /*
> +     * Mark the TB as invalid *after* it's been removed from tb_hash, which
> +     * eliminates the need to check this bit on lookups.
> +     */
> +    tb->invalid = true;

I believe you need atomic_store_release here.  Previously we were relying on 
the lock acquisition in qht_remove to provide the required memory barrier.

We definitely need to make sure this reaches memory before we zap the TB in the 
CPU_FOREACH loop.


r~