linux-kernel - Re: [PATCH v6 2/3] x86, apic: Add disable_cpu

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Message-ID: <528EA874.9010609@jp.fujitsu.com>
Date:	Fri, 22 Nov 2013 09:42:28 +0900
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.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 v6 2/3] x86, apic: Add disable_cpu_apicid kernel parameter

(2013/11/22 6:33), Vivek Goyal wrote:
> On Thu, Nov 21, 2013 at 11:00:44AM +0900, HATAYAMA Daisuke wrote:
>
> [..]
>> @@ -2122,6 +2129,19 @@ void generic_processor_info(int apicid, int version)
>>   	bool boot_cpu_detected = physid_isset(boot_cpu_physical_apicid,
>>   				phys_cpu_present_map);
>>
>> +	if (disabled_cpu_apicid != BAD_APICID &&
>> +	    disabled_cpu_apicid != boot_cpu_physical_apicid &&
>
> Hi Hatayama,
>
> So we are comparing disabled_cpu_apicid with boot_cpu_physical_apicid
> to make sure that one can not disable the cpu we are booting on. Can
> we just read the apic id of booting cpu in local variable and compare
> against that?
>
> Something like as follows.
>
> 	if (disabled_cpu_apicid != BAD_APICID &&
> 	    disabled_cpu_apicid == apicid &&
> 	    disabled_cpu_apicid != read_apic_id()) {
> 		/* Disable cpu */	
> 	}
>
> If above works, you will not need first patch in the series?
>

Yes, I came up with the idea, too. But doing this means we leave two different
ways boot_cpu_physical_apicid is used at boot, which seemed incomplete as a
patch. Also, then we could even lost the reason why boot_cpu_physical_apicid
exists.

But, it's true that the 1st patch causes one more reviewing point. I'll
remove it and fix the 2nd patch just as you suggested here.

-- 
Thanks.
HATAYAMA, Daisuke

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