Re: [Qemu-devel] target-i386: clear bsp bit when designating bsp

["Andreas Färber" <afaerber@suse.de>]

Am 07.04.2015 um 15:44 schrieb Denis V. Lunev:
> On 07/04/15 16:29, Paolo Bonzini wrote:
>>
>>
>> On 07/04/2015 15:26, Denis V. Lunev wrote:
>>> On 07/04/15 16:18, Paolo Bonzini wrote:
>>>>
>>>>
>>>> On 07/04/2015 13:57, Andreas Färber wrote:
>>>>>>> If this is some issue with sync'ing state back and forth before
>>>>>>> QEMU and
>>>>>>> KVM then the real issue has not been explained.
>>>>> Hm, hw/intc/apic_common.c:apic_reset_common() has:
>>>>>
>>>>>       bsp = cpu_is_bsp(s->cpu);
>>>>>       s->apicbase = APIC_DEFAULT_ADDRESS |
>>>>>           (bsp ? MSR_IA32_APICBASE_BSP : 0) |
>>>>> MSR_IA32_APICBASE_ENABLE;
>>>>>
>>>>> What this is doing is really:
>>>>>
>>>>>       bsp = cpu_get_apic_base(s->cpu->apic_state) &
>>>>> MSR_IA32_APICBASE_BSP;
>>>>>       s->apicbase = APIC_DEFAULT_ADDRESS |
>>>>>           (bsp ? MSR_IA32_APICBASE_BSP : 0) |
>>>>> MSR_IA32_APICBASE_ENABLE;
>>>>>
>>>>> Unless I'm missing something, since we are in the APIC device's reset
>>>>> function, this is effectively a twisted way of writing:
>>>>>
>>>>>       bsp = s->apicbase & MSR_IA32_APICBASE_BSP;
>>>>>       s->apicbase = APIC_DEFAULT_ADDRESS |
>>>>>           (bsp ? MSR_IA32_APICBASE_BSP : 0) |
>>>>> MSR_IA32_APICBASE_ENABLE;
>>>>
>>>> Yes, this is more readable.
>>>
>>> just $0.02 :)
>>>
>>> why don't
>>>          bsp = s->apicbase & MSR_IA32_APICBASE_BSP;
>>>          s->apicbase =
>>>          APIC_DEFAULT_ADDRESS | bsp | MSR_IA32_APICBASE_ENABLE;
>>> in this case. This looks the same from the textual point of view.
>>
>> Yes.  Would you like to send a patch?
>>
>> Paolo
>>
> 
> no prob, just give me 2 minutes. Side note, bsp will become uint32_t
> and we will loose tracepoint inside cpu_get_apic_base() on this
> path...

Yes, I intentionally left it out above as I don't think we need to trace
the local usage here. Worth mentioning in the commit message though.

Regards,
Andreas

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