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Re: [Qemu-devel] [PATCH v4 09/10] tcg: Clean up direct block chaining sa
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [PATCH v4 09/10] tcg: Clean up direct block chaining safety checks |
Date: |
Thu, 21 Apr 2016 16:45:47 +0100 |
User-agent: |
mu4e 0.9.17; emacs 25.0.92.6 |
Sergey Fedorov <address@hidden> writes:
> On 21/04/16 16:18, Alex Bennée wrote:
>> Sergey Fedorov <address@hidden> writes:
>>> diff --git a/cpu-exec.c b/cpu-exec.c
>>> index bbfcbfb54385..065cc9159477 100644
>>> --- a/cpu-exec.c
>>> +++ b/cpu-exec.c
>>> @@ -508,11 +508,8 @@ int cpu_exec(CPUState *cpu)
>>> next_tb = 0;
>>> tcg_ctx.tb_ctx.tb_invalidated_flag = 0;
>>> }
>>> - /* see if we can patch the calling TB. When the TB
>>> - spans two pages, we cannot safely do a direct
>>> - jump. */
>>> - if (next_tb != 0 && tb->page_addr[1] == -1
>>> - && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
>>> + /* See if we can patch the calling TB. */
>>> + if (next_tb != 0 &&
>>> !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
>> A pointer to the definitive comment helps ;-)
>>
>> /* See if we can patch the calling TB, see tcg_gen_goto_tb */
>
> I'm not so sure that the comment for tcg_gen_goto_tb() would be of much
> use here. Actually, what we check here is if we know the calling TB
> (what is called 'next_tb' here so far) and if logging settings don't
> forbid us to chain TBs. The note in the comment for tcg_gen_goto_tb() is
> all about when goto_tb TCG ops can be emitted by the target translation
> code, not so relevant here, I suppose.
True, it makes more sense on the following patches. It's not a major
thing.
>
> Kind regards,
> Sergey
>
>>
>>> tb_add_jump((TranslationBlock *)(next_tb &
>>> ~TB_EXIT_MASK),
>>> next_tb & TB_EXIT_MASK, tb);
>>> }
> (snip)
>>> diff --git a/tcg/tcg-op.h b/tcg/tcg-op.h
>>> index c446d3dc7293..ace39619ef89 100644
>>> --- a/tcg/tcg-op.h
>>> +++ b/tcg/tcg-op.h
>>> @@ -753,6 +753,16 @@ static inline void tcg_gen_exit_tb(uintptr_t val)
>>> tcg_gen_op1i(INDEX_op_exit_tb, val);
>>> }
>>>
>>> +/**
>>> + * tcg_gen_goto_tb() - output goto_tb TCG operation
>>> + * @idx: Direct jump slot index (0 or 1)
>>> + *
>>> + * See tcg/README for more info about this TCG operation.
>>> + *
>>> + * NOTE: Direct jumps with goto_tb are only safe within the pages this TB
>>> + * resides in because we don't take care of direct jumps when address
>>> mapping
>>> + * changes, e.g. in tlb_flush().
>>> + */
>>> void tcg_gen_goto_tb(unsigned idx);
>>>
>>> #if TARGET_LONG_BITS == 32
--
Alex Bennée
- [Qemu-devel] [PATCH v4 00/10] tcg: Direct block chaining clean-up, Sergey Fedorov, 2016/04/20
- [Qemu-devel] [PATCH v4 03/10] tcg: Rearrange tb_link_page() to avoid forward declaration, Sergey Fedorov, 2016/04/20
- [Qemu-devel] [PATCH v4 04/10] tcg: Init TB's direct jumps before making it visible, Sergey Fedorov, 2016/04/20
- [Qemu-devel] [PATCH v4 01/10] tcg: Clean up direct block chaining data fields, Sergey Fedorov, 2016/04/20
- [Qemu-devel] [PATCH v4 10/10] tcg: Allow goto_tb to any target PC in user mode, Sergey Fedorov, 2016/04/20
- [Qemu-devel] [PATCH v4 05/10] tcg: Clarify thread safety check in tb_add_jump(), Sergey Fedorov, 2016/04/20
- [Qemu-devel] [PATCH v4 06/10] tcg: Rename tb_jmp_remove() to tb_remove_from_jmp_list(), Sergey Fedorov, 2016/04/20
- [Qemu-devel] [PATCH v4 07/10] tcg: Extract removing of jumps to TB from tb_phys_invalidate(), Sergey Fedorov, 2016/04/20
- Re: [Qemu-devel] [PATCH v4 00/10] tcg: Direct block chaining clean-up, Alex Bennée, 2016/04/28