linux-kernel - Re: [tip:x86/apic] x86, apic, kexec: Add disable_cpu

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Date:	Wed, 15 Jan 2014 19:25:11 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	hpa@...or.com, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	d.hatayama@...fujitsu.com
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/apic] x86, apic, kexec: Add disable_cpu_apicid kernel
 parameter


* tip-bot for HATAYAMA Daisuke <tipbot@...or.com> wrote:

>  /*
> + * Processor to be disabled specified by kernel parameter
> + * disable_cpu_apicid=<int>, mostly used for the kdump 2nd kernel to
> + * avoid undefined behaviour caused by sending INIT from AP to BSP.
> + */
> +unsigned int disabled_cpu_apicid = BAD_APICID;

Any reason why this isn't static & read_mostly?

> @@ -2114,6 +2121,39 @@ int generic_processor_info(int apicid, int version)
>  				phys_cpu_present_map);
>  
>  	/*
> +	 * boot_cpu_physical_apicid is designed to have the apicid
> +	 * returned by read_apic_id(), i.e, the apicid of the
> +	 * currently booting-up processor. However, on some platforms,
> +	 * it is temporarilly modified by the apicid reported as BSP

s/temporarily

> +	 * through MP table. Concretely:
> +	 *
> +	 * - arch/x86/kernel/mpparse.c: MP_processor_info()
> +	 * - arch/x86/mm/amdtopology.c: amd_numa_init()
> +	 * - arch/x86/platform/visws/visws_quirks.c: MP_processor_info()
> +	 *
> +	 * This function is executed with the modified
> +	 * boot_cpu_physical_apicid. So, disabled_cpu_apicid kernel
> +	 * parameter doesn't work to disable APs on kdump 2nd kernel.
> +	 *
> +	 * Since fixing handling of boot_cpu_physical_apicid requires
> +	 * another discussion and tests on each platform, we leave it
> +	 * for now and here we use read_apic_id() directly in this
> +	 * function, generic_processor_info().
> +	 */
> +	if (disabled_cpu_apicid != BAD_APICID &&
> +	    disabled_cpu_apicid != read_apic_id() &&
> +	    disabled_cpu_apicid == apicid) {
> +		int thiscpu = num_processors + disabled_cpus;
> +
> +		pr_warning("ACPI: Disabling requested cpu."
> +			   " Processor %d/0x%x ignored.\n",
> +			   thiscpu, apicid);

Why does this message say 'ACPI'? Shouldn't it say 'apic' instead?

Thanks,

	Ingo
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