linux-kernel - Re: [PATCH v4 1/3] x86, apic: Don't count the CPU with BP flag from MP table as booting-up CPU

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Date:	Tue, 12 Nov 2013 18:58:28 +0900
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	fengguang.wu@...el.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, bp@...en8.de, ebiederm@...ssion.com,
	akpm@...ux-foundation.org, hpa@...ux.intel.com, jingbai.ma@...com
Subject: Re: [PATCH v4 1/3] x86, apic: Don't count the CPU with BP flag from
 MP table as booting-up CPU

(2013/11/12 9:40), HATAYAMA Daisuke wrote:
> (2013/11/12 1:52), Vivek Goyal wrote:
>> On Mon, Nov 11, 2013 at 11:52:30AM +0900, HATAYAMA Daisuke wrote:
>>
>> [..]
>>> Looking at my past investigation, kernel/mpparse.c, mm/amdtopology.c and
>>> platform/visws/visws_quirks.c assumes that boot_cpu_physical_apicid
>>> has initial apicid of the BSP, not the current actual booting-up cpu.
>>>
>>> These three are called in get_smp_config() below. If either of them is
>>> called actually, boot_cpu_physical_apicid has the apicid different from
>>> the current actual booting-up cpu temporarily. But init_apic_mappings()
>>> soon modifies back the value to the one obtained by read_apic_id().
>>>
>>>          /*
>>>           * Read APIC and some other early information from ACPI tables.
>>>           */
>>>          acpi_boot_init();
>>>          sfi_init();
>>>          x86_dtb_init();
>>>
>>>          /*
>>>           * get boot-time SMP configuration:
>>>           */
>>>          if (smp_found_config)
>>>                  get_smp_config();
>>>
>>>          prefill_possible_map();
>>>
>>>          init_cpu_to_node();
>>>
>>>          init_apic_mappings();
>>>
>>> So, thanks to init_apic_mappings(), the patch set would work without the
>>> first patch... This is a careless point in this patch set.
>>>
>>
>> If init_apic_mappings(), is making sure that boot_cpu_physical_apicid is
>> apic id of booting processor, and you don't need first patch of your
>> series, then I think atleast re-post your patch series without first
>> patch.
>>
>
> Yes, I'll repost soon.
>
>> And then there can be another series which looks into whether we need
>> two different variables or not and if we do, then a separate variable
>> bsp_physical_apicid will track the bsp id as reported by BIOS and
>> boot_cpu_physical_apicid will track apic id of booting cpu. This might
>> a very big and slow cleanup. So I think blocking the first patch series
>> behind it might not make much sense.
>>
>
> Yes, the current handling of boot_cpu_physical_apicid looks strange and
> should be cleaned up, but the cleaning up needs reviewing together with
> the maintainers for the corresponding part; in particular, it can be
> lengthy for the reviewing on amdtopology.c. I leave this as another
> work for the time being.
>

Sorry for my confusion. It's necessary to introduce a new variable to keep
the initial APIC ID for the processor with BSP flag on IA32_APIC_BASE MSR,
which is needed in case of AP is specified by disable_cpu_apicid and using
MP table.

I've posted new v5 patch set a little ago. Could you please review it?

-- 
Thanks.
HATAYAMA, Daisuke

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