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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Wed, 14 Jun 2017 12:45:34 +0100
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Subject: Re: [Qemu-devel] [PATCH] target/aarch64: exit to main loop after
 handling MSR
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>, "Emilio G. Cota" <cota@braap.org>, peter.maydell@linaro.org, edgar.iglesias@xilinx.com, qemu-devel@nongnu.org, Peter Crosthwaite <crosthwaite.peter@gmail.com>, "open list:ARM" <qemu-arm@nongnu.org>


Paolo Bonzini <pbonzini@redhat.com> 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?

>
> Thanks,
>
> Paolo


--
Alex Bennée