[PATCH v7 0/3] x86, apic, kexec: Add disable_cpu_apic kernel parameter

[PATCH v7 0/3] x86, apic, kexec: Add disable_cpu_apic kernel parameter

[HATAYAMA Daisuke]

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.

ChangeLog

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

---

HATAYAMA Daisuke (2):
      x86, apic: Add disable_cpu_apicid kernel parameter
      Documentation, x86, apic, kexec: Add disable_cpu_apicid kernel parameter


 Documentation/kernel-parameters.txt |    9 ++++++
 arch/x86/kernel/apic/apic.c         |   49 +++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)

-- 

Thanks.
HATAYAMA, Daisuke

[PATCH v7 1/2] x86, apic: Add disable_cpu_apicid kernel parameter

[HATAYAMA Daisuke]

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.

boot_cpu_physical_apicid is designed to have the apicid returned by
read_apic_id(). However, on some platforms, it is temporarilly
modified by the apicid reported as BSP through MP table. This function
is called with the modified boot_cpu_physical_apicid.

On the platforms, boot_cpu_physical_apicid is always forced to be the
apicid of the BSP. Then, disabled_cpu_apicid kernel parameter doesn't
work well for apicids for APs.

Here we leave improvement of handling boot_cpu_physical_apicid as
another work for now since the temporary modification is done on
differnet platforms and tests on each platform are required. As a
workaround, we directly update boot_cpu_physical_apicid by
read_apic_id().

Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
---
 arch/x86/kernel/apic/apic.c |   49 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index d278736..a94f618 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);
@@ -2111,9 +2118,42 @@ void disconnect_bsp_APIC(int virt_wire_setup)
 int generic_processor_info(int apicid, int version)
 {
 	int cpu, max = nr_cpu_ids;
+	/*
+	 * boot_cpu_physical_apicid is designed to have the apicid
+	 * returned by read_apic_id(). 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.
+	 *
+	 * 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 by updating
+	 * global scope of boot_cpu_physical_id with the local one.
+	 */
+	unsigned int boot_cpu_physical_apicid = read_apic_id();
 	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 &&
+	    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);

[PATCH v7 2/2] Documentation, x86, apic, kexec: Add disable_cpu_apicid kernel parameter

[HATAYAMA Daisuke]

Add disable_cpu_apicid kernel parameter to disable the CPU with the
specified number of initial APIC ID, 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.

Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
---
 Documentation/kernel-parameters.txt |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 50680a5..dd77bec 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,KEXEC,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.

Re: [PATCH v7 1/2] x86, apic: Add disable_cpu_apicid kernel parameter

[Vivek Goyal]

On Wed, Nov 27, 2013 at 11:00:48AM +0900, HATAYAMA Daisuke wrote:
> 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.
> 
> boot_cpu_physical_apicid is designed to have the apicid returned by
> read_apic_id(). However, on some platforms, it is temporarilly
> modified by the apicid reported as BSP through MP table. This function
> is called with the modified boot_cpu_physical_apicid.
> 
> On the platforms, boot_cpu_physical_apicid is always forced to be the
> apicid of the BSP. Then, disabled_cpu_apicid kernel parameter doesn't
> work well for apicids for APs.
> 
> Here we leave improvement of handling boot_cpu_physical_apicid as
> another work for now since the temporary modification is done on
> differnet platforms and tests on each platform are required. As a
> workaround, we directly update boot_cpu_physical_apicid by
> read_apic_id().
> 
> Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
> ---
>  arch/x86/kernel/apic/apic.c |   49 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index d278736..a94f618 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);
> @@ -2111,9 +2118,42 @@ void disconnect_bsp_APIC(int virt_wire_setup)
>  int generic_processor_info(int apicid, int version)
>  {
>  	int cpu, max = nr_cpu_ids;
> +	/*
> +	 * boot_cpu_physical_apicid is designed to have the apicid
> +	 * returned by read_apic_id(). 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.
> +	 *
> +	 * 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 by updating
> +	 * global scope of boot_cpu_physical_id with the local one.
> +	 */
> +	unsigned int boot_cpu_physical_apicid = read_apic_id();

I think this is confusing. Why are you trying to define a local variable
with same name as global variable. There is no need. I think if we
simply put the comment there that why are we not making use of
boot_cpu_physical_apicid, that is good enough and directly read
the apic id.

	if (disabled_cpu_apicid != BAD_APICID &&
	    disabled_cpu_apicid != read_apic_id() &&
	    disabled_cpu_apicid == apicid) {

	}

Thanks
Vivek

>  	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 &&
> +	    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);

Re: [PATCH v7 2/2] Documentation, x86, apic, kexec: Add disable_cpu_apicid kernel parameter

[Vivek Goyal]

On Wed, Nov 27, 2013 at 11:00:53AM +0900, HATAYAMA Daisuke wrote:
> Add disable_cpu_apicid kernel parameter to disable the CPU with the
> specified number of initial APIC ID, 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.
> 
> Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>

I guess you don't require a separate patch for documentation. Just merge
it with previous patch. So this becomes a single patch fix and not a 
series.

Thanks
Vivek
> ---
>  Documentation/kernel-parameters.txt |    9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 50680a5..dd77bec 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,KEXEC,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.

Re: [PATCH v7 1/2] x86, apic: Add disable_cpu_apicid kernel parameter

[HATAYAMA Daisuke]

(2013/11/28 0:10), Vivek Goyal wrote:
> On Wed, Nov 27, 2013 at 11:00:48AM +0900, HATAYAMA Daisuke wrote:
>> 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.
>>
>> boot_cpu_physical_apicid is designed to have the apicid returned by
>> read_apic_id(). However, on some platforms, it is temporarilly
>> modified by the apicid reported as BSP through MP table. This function
>> is called with the modified boot_cpu_physical_apicid.
>>
>> On the platforms, boot_cpu_physical_apicid is always forced to be the
>> apicid of the BSP. Then, disabled_cpu_apicid kernel parameter doesn't
>> work well for apicids for APs.
>>
>> Here we leave improvement of handling boot_cpu_physical_apicid as
>> another work for now since the temporary modification is done on
>> differnet platforms and tests on each platform are required. As a
>> workaround, we directly update boot_cpu_physical_apicid by
>> read_apic_id().
>>
>> Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
>> ---
>>   arch/x86/kernel/apic/apic.c |   49 +++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 49 insertions(+)
>>
>> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
>> index d278736..a94f618 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);
>> @@ -2111,9 +2118,42 @@ void disconnect_bsp_APIC(int virt_wire_setup)
>>   int generic_processor_info(int apicid, int version)
>>   {
>>   	int cpu, max = nr_cpu_ids;
>> +	/*
>> +	 * boot_cpu_physical_apicid is designed to have the apicid
>> +	 * returned by read_apic_id(). 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.
>> +	 *
>> +	 * 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 by updating
>> +	 * global scope of boot_cpu_physical_id with the local one.
>> +	 */
>> +	unsigned int boot_cpu_physical_apicid = read_apic_id();
>
> I think this is confusing. Why are you trying to define a local variable
> with same name as global variable. There is no need. I think if we
> simply put the comment there that why are we not making use of
> boot_cpu_physical_apicid, that is good enough and directly read
> the apic id.
>
> 	if (disabled_cpu_apicid != BAD_APICID &&
> 	    disabled_cpu_apicid != read_apic_id() &&
> 	    disabled_cpu_apicid == apicid) {
>
> 	}
>

Because there are also other occurrences of boot_cpu_physical_apicid in the
same function, and defining the local variable with the same name needs
one line only, and it's a temporary workaround change, I think it unnatural
to replace boot_cpu_physical_apicid even temporarily.

-- 
Thanks.
HATAYAMA, Daisuke