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Re: [Qemu-devel] [PATCH v3 07/11] tcg: Prepare TB invalidation for lockl
From: |
Sergey Fedorov |
Subject: |
Re: [Qemu-devel] [PATCH v3 07/11] tcg: Prepare TB invalidation for lockless TB lookup |
Date: |
Thu, 14 Jul 2016 16:11:20 +0300 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 |
On 14/07/16 15:59, Alex Bennée wrote:
> Sergey Fedorov <address@hidden> writes:
>
>> From: Sergey Fedorov <address@hidden>
>>
>> When invalidating a translation block, set an invalid CPU state into the
>> TranslationBlock structure first. All subsequent changes are ordered
>> after it with smp_wmb(). This pairs with implied smp_rmb() of
>> qht_lookup() in tb_find_physical().
>>
>> As soon as the TB is marked with an invalid CPU state, there is no need
>> to remove it from CPU's 'tb_jmp_cache'. However it will be necessary to
>> recheck whether the target TB is still valid after acquiring 'tb_lock'
>> but before calling tb_add_jump() since TB lookup is to be performed out
>> of 'tb_lock' in future. Note that we don't have to check 'last_tb' since
>> it is safe to patch an already invalidated TB since it will not be
>> executed anyway.
> This looks fine. So I guess it's possible for the block to have been
> looked up just before it gets invalidated and get one final run but not
> get patched?
Yes, exactly.
Thanks,
Sergey
>
> Reviewed-by: Alex Bennée <address@hidden>
>
>> Suggested-by: Paolo Bonzini <address@hidden>
>> Signed-off-by: Sergey Fedorov <address@hidden>
>> Signed-off-by: Sergey Fedorov <address@hidden>
>> ---
>> cpu-exec.c | 2 +-
>> translate-all.c | 12 +++---------
>> 2 files changed, 4 insertions(+), 10 deletions(-)
>>
>> diff --git a/cpu-exec.c b/cpu-exec.c
>> index c973e3b85922..07dc50c56e8d 100644
>> --- a/cpu-exec.c
>> +++ b/cpu-exec.c
>> @@ -352,7 +352,7 @@ static inline TranslationBlock *tb_find_fast(CPUState
>> *cpu,
>> /* Check if translation buffer has been flushed */
>> if (cpu->tb_flushed) {
>> cpu->tb_flushed = false;
>> - } else {
>> + } else if (!tb_is_invalid(tb)) {
>> tb_add_jump(last_tb, tb_exit, tb);
>> }
>> }
>> diff --git a/translate-all.c b/translate-all.c
>> index 788fed1e0765..ee8308209350 100644
>> --- a/translate-all.c
>> +++ b/translate-all.c
>> @@ -986,11 +986,13 @@ static inline void tb_jmp_unlink(TranslationBlock *tb)
>> /* invalidate one TB */
>> void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr)
>> {
>> - CPUState *cpu;
>> PageDesc *p;
>> uint32_t h;
>> tb_page_addr_t phys_pc;
>>
>> + tb_mark_invalid(tb);
>> + smp_wmb();
>> +
>> /* 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);
>> @@ -1008,14 +1010,6 @@ void tb_phys_invalidate(TranslationBlock *tb,
>> tb_page_addr_t page_addr)
>> invalidate_page_bitmap(p);
>> }
>>
>> - /* remove the TB from the hash list */
>> - h = tb_jmp_cache_hash_func(tb->pc);
>> - CPU_FOREACH(cpu) {
>> - if (atomic_read(&cpu->tb_jmp_cache[h]) == tb) {
>> - atomic_set(&cpu->tb_jmp_cache[h], NULL);
>> - }
>> - }
>> -
>> /* suppress this TB from the two jump lists */
>> tb_remove_from_jmp_list(tb, 0);
>> tb_remove_from_jmp_list(tb, 1);
>
> --
> Alex Bennée
- [Qemu-devel] [PATCH v3 02/11] cpu-exec: Pass last_tb by value to tb_find_fast(), (continued)
- [Qemu-devel] [PATCH v3 05/11] target-i386: Remove redundant HF_SOFTMMU_MASK, Sergey Fedorov, 2016/07/12
- [Qemu-devel] [PATCH v3 08/11] tcg: set up tb->page_addr before insertion, Sergey Fedorov, 2016/07/12
- [Qemu-devel] [PATCH v3 07/11] tcg: Prepare TB invalidation for lockless TB lookup, Sergey Fedorov, 2016/07/12
- [Qemu-devel] [PATCH v3 09/11] tcg: cpu-exec: remove tb_lock from the hot-path, Sergey Fedorov, 2016/07/12
- [Qemu-devel] [PATCH v3 06/11] tcg: Introduce tb_mark_invalid() and tb_is_invalid(), Sergey Fedorov, 2016/07/12
Re: [Qemu-devel] [PATCH v3 06/11] tcg: Introduce tb_mark_invalid() and tb_is_invalid(), Alex Bennée, 2016/07/14