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Re: [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling
From: |
Alex Bennée |
Subject: |
Re: [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling MSR |
Date: |
Wed, 14 Jun 2017 13:14:21 +0100 |
User-agent: |
mu4e 0.9.19; emacs 25.2.50.3 |
Paolo Bonzini <address@hidden> writes:
> On 14/06/2017 13:45, Alex Bennée wrote:
>>
>> Paolo Bonzini <address@hidden> writes:
>>
>>> On 14/06/2017 06:48, Richard Henderson wrote:
>>>>>
>>>>> Commit e75449a3 ("target/aarch64: optimize indirect branches") causes
>>>>> a regression by which aarch64 guests freeze under TCG with -smp > 1,
>>>>> even with `-accel accel=tcg,thread=single' (i.e. MTTCG disabled).
>>>>>
>>>>> I isolated the problem to the MSR handler. This patch forces an exit
>>>>> after the handler is executed, which fixes the regression.
>>>>
>>>> Why would that be? The cpu_get_tb_cpu_state within helper_lookup_tb_ptr
>>>> is supposed to read the new state that the msr handler would have
>>>> installed.
>>>
>>> Could some of these cause an interrupt, or some other change in the
>>> cpu_exec flow?
>>
>> Well what I was observing was the secondary_start_kernel stalling and
>> leaving the main cpu spinning. The msr is actually:
>>
>> local_irq_enable();
>> local_fiq_enable();
>>
>> Which I assume would re-enable IRQs if they are ready to go. However I
>> guess if we sink into our cpu_idle without exiting the main loop we
>> never set any pending IRQs?
>
> Then Emilio's patch, if a bit of a heavy hammer, is correct. After
> aa64_daif_write needs you need an exit_tb so that arm_cpu_exec_interrupt
> is executed again.
This is a case of cpu->interrupt_request being pending but not having
set cpu->icount_decr yet to signal the exit. Wouldn't another approach
(that didn't involve futzing with each front-end) to be to check
cpu->interrupt_request and force the exit in lookup_tb_ptr?
>
> Compare with this from the x86 front-end:
>
> /* if irq were inhibited with HF_INHIBIT_IRQ_MASK, we clear
> the flag and abort the translation to give the irqs a
> change to be happen */
> if (dc->tf || dc->singlestep_enabled ||
> (flags & HF_INHIBIT_IRQ_MASK)) {
> gen_jmp_im(pc_ptr - dc->cs_base);
> gen_eob(dc);
> break;
> }
>
> (This triggers one instruction after a STI instruction, due to how x86's
> "interrupt shadow" work, so it doesn't happen immediately after
> helper_sti; but the idea is the same).
>
> Paolo
--
Alex Bennée
- Re: [Qemu-arm] [RFC DEBUG PATCH 3/3] translate-a64: fix lookup_tb_ptr hang (DEBUG!), (continued)
- Re: [Qemu-arm] [RFC DEBUG PATCH 3/3] translate-a64: fix lookup_tb_ptr hang (DEBUG!), Alex Bennée, 2017/06/10
- Re: [Qemu-arm] [RFC DEBUG PATCH 3/3] translate-a64: fix lookup_tb_ptr hang (DEBUG!), Richard Henderson, 2017/06/10
- Re: [Qemu-arm] [RFC DEBUG PATCH 3/3] translate-a64: fix lookup_tb_ptr hang (DEBUG!), Emilio G. Cota, 2017/06/11
- Re: [Qemu-arm] [RFC DEBUG PATCH 3/3] translate-a64: fix lookup_tb_ptr hang (DEBUG!), Alex Bennée, 2017/06/12
- [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling MSR, Emilio G. Cota, 2017/06/13
- Re: [Qemu-arm] [Qemu-devel] [PATCH] target/aarch64: exit to main loop after handling MSR, no-reply, 2017/06/13
- Re: [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling MSR, Richard Henderson, 2017/06/14
- Re: [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling MSR, Paolo Bonzini, 2017/06/14
- Re: [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling MSR, Alex Bennée, 2017/06/14
- Re: [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling MSR, Paolo Bonzini, 2017/06/14
- Re: [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling MSR,
Alex Bennée <=
- Re: [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling MSR, Paolo Bonzini, 2017/06/14
- Re: [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling MSR, Alex Bennée, 2017/06/14
- Re: [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling MSR, Paolo Bonzini, 2017/06/14
- Re: [Qemu-arm] [PATCH] target/aarch64: exit to main loop after handling MSR, Alex Bennée, 2017/06/14