Re: [PATCH v10] x86, apic, kexec, Documentation: Adddisable_cpu_apic kernel parameter

[Vivek Goyal]

On Wed, Dec 04, 2013 at 05:10:58PM +0900, HATAYAMA Daisuke wrote:
> This patch set is to allow kdump 2nd kernel to wake up multiple CPUs,
> a continueing work from:
> 
>   [PATCH v3 0/2] x86, apic, kdump: Disable BSP if boot cpu is AP
>   https://lkml.org/lkml/2013/10/16/300.
> 
> At v4, basic design has changed. Now users need to figure out initial
> APIC ID of BSP in the 1st kernel and configures kernel parameter for
> the 2nd kernel manually using disable_cpu_apicid kernel parameter,
> which is newly introduced by this patch set. This design is more
> flexible than the previous version in that we no longer have to rely
> on ACPI/MP table to get initial APIC ID of BSP.
> 
> Sorry, this patch set have not include in-source documentation
> requested by Borislav Petkov yet, but I'll post it later separately,
> which would be better to focus on documentation reviewing.

Hi hpa,

Can you please consider this patch for inclusion.

Thanks
Vivek

> 
> ChangeLog
> 
> v9 => v10)
> 
> - Remove KEXEC tag from the description of disable_cpu_apicid since
>   the parameter is generic, independent of CONFIG_KEXEC, at least in
>   this version.
> 
> v8 => v9)
> 
> - Rebased on top of v3.13-rc2
> 
> - Call read_apic_id() in case of disable_cpu_apiid only in
>   generic_processor_info().
> 
> v7 => v8)
> 
> - Merge the patch that adds new descption in
>   Documentations/kernel-parameters.txt in the first patch.
> 
> - Call read_apic_id() directly in generic_processor_info() instead of
>   overriding global boot_cpu_physical_apicid with the local variable
>   with the same name.
> 
> v6 => v7)
> 
> - Rebased on top of v3.13-rc1
> 
> - Remove a patch that cleans up the code around
>   x86_cpu_physical_apicid. Instead, use read_apic_id() directly in
>   generic_processor_info(). The clean up removed here will be done in
>   different patch set.
> 
> v5 => v6)
> 
> - Remove use of rdmsr(IA32_APIC_BASE) to initialize
>   bsp_physical_apicid since the MSR doesn't work well on some cluster
>   systems, suggested by HPA. Also, current users of the variable
>   expects the initial apicid reported through MP table only; removing
>   the use of the MSR is not problematic.
> 
> - Rename bsp_physical_apicid as bios_bsp_physical_apicid to make it
>   clear that the apidid contained there is the one reported from some
>   BIOS table. Also, initialize it not only by MP table but also by
>   ACPI MADT.
> 
> - Change message displayed when specified cpu is disabled from:
> 
>   ACPI: Disable specified CPU. Processor 0/0x0 ignored.
> 
>   to:
> 
>   ACPI: Disabling requested cpu. Processor 0/0x0 ignored.
> 
> v4 => v5)
> 
> - Rebased on top of v3.12
> 
> - Introduce bsp_physical_apicid that has the initial APIC ID for the
>   processor with BSP flag on IA32_APIC_BASE MSR. Without this,
>   boot_cpu_physical_apicid has temporarilly the value around MP table
>   related codes, although it's designed to have the initial APIC ID
>   for the processor that is doing the boot up. Use the
>   bsp_physical_apicid in MP table related codes; no impact on
>   semantics at runtime there.
> 
> v3 => v4)
> 
> - Rebased on top of v3.12-rc6
> 
> - Basic design has been changed. Now users need to figure out initial
>   APIC ID of BSP in the 1st kernel and configures kernel parameter for
>   the 2nd kernel manually using disable_cpu_apic kernel parameter to
>   be newly introduced in this patch set. This design is more flexible
>   than the previous version in that we no longer have to rely on
>   ACPI/MP table to get initial APIC ID of BSP.
> 
> v2 => v3)
> 
> - Change default value of boot_cpu_is_bsp to true.
> 
> - Before executing rdmsr(MSR_IA32_APICBASE), check if the number of
>   processor family is larger than or equal to 6 in order to avoid
>   invalid opcode exception on processors where MSR_IA32_APICBASE is
>   not supported.
> 
> v1 => v2)
> 
> - Rebased on top of v3.12-rc5.
> 
> - Fix linking time error of boot_cpu_is_bsp_init() in case of
>   CONFIG_LOCAL_APIC disabled by adding empty static inline function
>   instead.
> 
> - Fix missing feature check by means of cpu_has_apic macro in
>   boot_cpu_is_bsp_init() before calling rdmsr_safe(MSR_IA32_APICBASE).
> 
>   NOTE: I've checked local apic-present case only; I don't have any
>   x86 processor without local apic.
> 
> - Add __init annotation to boot_cpu_is_bsp_init().
> 
> Test
> 
> - built with and without CONFIG_LOCAL_APIC
> - tested x86_64 in case of acpi and MP table
> - tested disable_cpu_apicid=<n> to disable both AP and BSP
> 
> 
> >From d03e159d9479755b36ac7d4a7d323b3ce95481be Mon Sep 17 00:00:00 2001
> From: HATAYAMA Daisuke <d.hatayama@xxxxxxxxxxxxxx>
> Date: Tue, 3 Dec 2013 09:21:56 +0900
> Subject: [PATCH] x86, apic, kexec, Documentation: Add disable_cpu_apicid
>  kernel parameter
> 
> Add disable_cpu_apicid kernel parameter. To use this kernel parameter,
> specify an initial APIC ID of the corresponding CPU you want to
> disable.
> 
> This is mostly used for the kdump 2nd kernel to disable BSP to wake up
> multiple CPUs without causing system reset or hang due to sending INIT
> from AP to BSP.
> 
> Kdump users first figure out initial APIC ID of the BSP, CPU0 in the
> 1st kernel, for example from /proc/cpuinfo and then set up this kernel
> parameter for the 2nd kernel using the obtained APIC ID.
> 
> However, doing this procedure at each boot time manually is awkward,
> which should be automatically done by user-land service scripts, for
> example, kexec-tools on fedora/RHEL distributions.
> 
> This design is more flexible than disabling BSP in kernel boot time
> automatically in that in kernel boot time we have no choice but
> referring to ACPI/MP table to obtain initial APIC ID for BSP, meaning
> that the method is not applicable to the systems without such BIOS
> tables.
> 
> One assumption behind this design is that users get initial APIC ID of
> the BSP in still healthy state and so BSP is uniquely kept in
> CPU0. Thus, through the kernel parameter, only one initial APIC ID can
> be specified.
> 
> In a comparison with disabled_cpu_apicid, we use read_apic_id(), not
> boot_cpu_physical_apicid, because on some platforms, the variable is
> modified to the apicid reported as BSP through MP table and this
> function is executed with the temporarily modified
> boot_cpu_physical_apicid. As a result, disabled_cpu_apicid kernel
> parameter doesn't work well for apicids of APs.
> 
> Fixing the wrong handling of boot_cpu_physical_apicid requires some
> reviews and tests beyond some platforms and it could take some
> time. The fix here is a kind of workaround to focus on the main topic
> of this patch.
> 
> Signed-off-by: HATAYAMA Daisuke <d.hatayama@xxxxxxxxxxxxxx>
> ---
>  Documentation/kernel-parameters.txt |  9 +++++++
>  arch/x86/kernel/apic/apic.c         | 49 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 58 insertions(+)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 50680a5..4e5528c 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -774,6 +774,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  	disable=	[IPV6]
>  			See Documentation/networking/ipv6.txt.
>  
> +	disable_cpu_apicid= [X86,APIC,SMP]
> +			Format: <int>
> +			The number of initial APIC ID for the
> +			corresponding CPU to be disabled at boot,
> +			mostly used for the kdump 2nd kernel to
> +			disable BSP to wake up multiple CPUs without
> +			causing system reset or hang due to sending
> +			INIT from AP to BSP.
> +
>  	disable_ddw     [PPC/PSERIES]
>  			Disable Dynamic DMA Window support. Use this if
>  			to workaround buggy firmware.
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index d278736..6c0b7d5 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -75,6 +75,13 @@ unsigned int max_physical_apicid;
>  physid_mask_t phys_cpu_present_map;
>  
>  /*
> + * 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;
> +
> +/*
>   * Map cpu index to physical APIC ID
>   */
>  DEFINE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_cpu_to_apicid, BAD_APICID);
> @@ -2115,6 +2122,39 @@ 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
> +	 * 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);
> +
> +		disabled_cpus++;
> +		return -ENODEV;
> +	}
> +
> +	/*
>  	 * If boot cpu has not been detected yet, then only allow upto
>  	 * nr_cpu_ids - 1 processors and keep one slot free for boot cpu
>  	 */
> @@ -2592,3 +2632,12 @@ static int __init lapic_insert_resource(void)
>   * that is using request_resource
>   */
>  late_initcall(lapic_insert_resource);
> +
> +static int __init apic_set_disabled_cpu_apicid(char *arg)
> +{
> +	if (!arg || !get_option(&arg, &disabled_cpu_apicid))
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +early_param("disable_cpu_apicid", apic_set_disabled_cpu_apicid);
> -- 
> 1.8.3.1
> 
> -- 
> Thanks.
> HATAYAMA, Daisuke
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