Re: [PATCH v2] x86/acpi: Don't add CPUs that are not online capable

["Limonciello, Mario" <mario.limonciello@amd.com>]

On 8/16/2021 09:04, Rafael J. Wysocki wrote:
> On Fri, Aug 13, 2021 at 6:19 PM Mario Limonciello
> <mario.limonciello@amd.com> wrote:
>>
>> A number of systems are showing "hotplug capable" CPUs when they
>> are not really hotpluggable.  This is because the MADT has extra
>> CPU entries to support different CPUs that may be inserted into
>> the socket with different numbers of cores.
>>
>> Starting with ACPI 6.3 the spec has an Online Capable bit in the
>> MADT used to determine whether or not a CPU is hotplug capable
>> when the enabled bit is not set.
>>
>> Link: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fuefi.org%2Fhtmlspecs%2FACPI_Spec_6_4_html%2F05_ACPI_Software_Programming_Model%2FACPI_Software_Programming_Model.html%3F%23local-apic-flags&amp;data=04%7C01%7Cmario.limonciello%40amd.com%7Ce6a384bf25274f88b49508d960bee40a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637647195281368169%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=3MWJ5NcRVJ7TP4tJH6uQRbqfZKSqe5RHjGxGbQEP13E%3D&amp;reserved=0
>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>> ---
>>   arch/x86/kernel/acpi/boot.c | 10 ++++++++++
>>   include/acpi/actbl2.h       |  1 +
>>   2 files changed, 11 insertions(+)
>>
>> Changes from v1->v2:
>>   * Check the revision field in MADT to determine if it matches the
>>     bump from ACPI 6.3 as suggested by Hanjun Guo
>>   * Update description
>>
>> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
>> index e55e0c1fad8c..bfa69a5c9c0b 100644
>> --- a/arch/x86/kernel/acpi/boot.c
>> +++ b/arch/x86/kernel/acpi/boot.c
>> @@ -53,6 +53,8 @@ int acpi_ioapic;
>>   int acpi_strict;
>>   int acpi_disable_cmcff;
>>
>> +bool acpi_support_online_capable;
> 
> Missing static?

Ack, thanks.

> 
>> +
>>   /* ACPI SCI override configuration */
>>   u8 acpi_sci_flags __initdata;
>>   u32 acpi_sci_override_gsi __initdata = INVALID_ACPI_IRQ;
>> @@ -138,6 +140,8 @@ static int __init acpi_parse_madt(struct acpi_table_header *table)
>>
>>                  pr_debug("Local APIC address 0x%08x\n", madt->address);
>>          }
>> +       if (madt->header.revision >= 5)
>> +               acpi_support_online_capable = true;
>>
>>          default_acpi_madt_oem_check(madt->header.oem_id,
>>                                      madt->header.oem_table_id);
>> @@ -239,6 +243,12 @@ acpi_parse_lapic(union acpi_subtable_headers * header, const unsigned long end)
>>          if (processor->id == 0xff)
>>                  return 0;
>>
>> +       /* don't register processors that can not be onlined */
>> +       if (acpi_support_online_capable &&
>> +           !(processor->lapic_flags & ACPI_MADT_ENABLED) &&
>> +           !(processor->lapic_flags & ACPI_MADT_ONLINE_CAPABLE))
>> +               return 0;
>> +
>>          /*
>>           * We need to register disabled CPU as well to permit
>>           * counting disabled CPUs. This allows us to size
>> diff --git a/include/acpi/actbl2.h b/include/acpi/actbl2.h
>> index 2069ac38a4e2..fae45e383987 100644
>> --- a/include/acpi/actbl2.h
>> +++ b/include/acpi/actbl2.h
> 
> The one below is an ACPICA change and I'd prefer it to be integrated
> via the upstream ACPICA.
> 
> Could you prepare an ACPICA pull request for just the bit below and
> send it via GitHub?

Sure thing.
http://github.com/acpica/acpica/pull/708/

They said they would take it later this month or next month.

Given that, how do you want to proceed with the first part of this?

Should I send a 2 patch series that will add the MADT bit to actbl2.h in 
advance of their next release, or should I wait to resubmit until after 
their next release and you've brought it into your tree?

> 
>> @@ -808,6 +808,7 @@ struct acpi_madt_multiproc_wakeup_mailbox {
>>   /* MADT Local APIC flags */
>>
>>   #define ACPI_MADT_ENABLED           (1)        /* 00: Processor is usable if set */
>> +#define ACPI_MADT_ONLINE_CAPABLE    (2)        /* 01: System HW supports enabling processor at runtime */
>>
>>   /* MADT MPS INTI flags (inti_flags) */
>>
>> --