Re: [Qemu-devel] [PATCH v2 2/6] tcg: set up tb->page_addr before insertion

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 07/07/16 17:08, Sergey Fedorov wrote:
> On 05/07/16 19:18, Alex Bennée wrote:
>> This ensures that if we find the TB on the slow path that tb->page_addr
>> is correctly set before being tested.
>>
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> Reveiwed-by: Sergey Fedorov <sergey.fedorov@linaro.org>

However, we may need to use smp_wmb() here paired with smp_rmb() in
tb_find_fast().

Alternatively, QHT might provide some explicit guarantee about memory
ordering around qht_insert() and qht_lookup(). Actually, there is
already right ordering thanks to seqlock operations in QHT
implementation. This means we could elide explicit memory barrier from
the first patch as well.

Kind regards,
Sergey

>
>> ---
>>  translate-all.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/translate-all.c b/translate-all.c
>> index 96efe48..97e834a 100644
>> --- a/translate-all.c
>> +++ b/translate-all.c
>> @@ -1126,10 +1126,6 @@ static void tb_link_page(TranslationBlock *tb, tb_page_addr_t phys_pc,
>>  {
>>      uint32_t h;
>>  
>> -    /* add in the hash table */
>> -    h = tb_hash_func(phys_pc, tb->pc, tb->flags);
>> -    qht_insert(&tcg_ctx.tb_ctx.htable, tb, h);
>> -
>>      /* add in the page list */
>>      tb_alloc_page(tb, 0, phys_pc & TARGET_PAGE_MASK);
>>      if (phys_page2 != -1) {
>> @@ -1138,6 +1134,10 @@ static void tb_link_page(TranslationBlock *tb, tb_page_addr_t phys_pc,
>>          tb->page_addr[1] = -1;
>>      }
>>  
>> +    /* add in the hash table */
>> +    h = tb_hash_func(phys_pc, tb->pc, tb->flags);
>> +    qht_insert(&tcg_ctx.tb_ctx.htable, tb, h);
>> +
>>  #ifdef DEBUG_TB_CHECK
>>      tb_page_check();
>>  #endif