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:	Mon, 11 Nov 2013 11:52:03 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc:	hpa@...ux.intel.com, ebiederm@...ssion.com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	bp@...en8.de, akpm@...ux-foundation.org, fengguang.wu@...el.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

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.  

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.

Thanks
Vivek
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