linux-kernel - Re: [PATCH v3 2/2] x86/acpi: Don't add CPUs that are not online capable

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Date:   Mon, 13 Sep 2021 13:30:21 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Cc:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:SUSPEND TO RAM" <linux-pm@...r.kernel.org>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] x86/acpi: Don't add CPUs that are not online
 capable

On 9/13/2021 12:23, Rafael J. Wysocki wrote:
> On Wed, Sep 8, 2021 at 11:41 PM Mario Limonciello
> <mario.limonciello@....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%7C081016240ab94e72822d08d976db3d0a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637671506287828485%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=0vIs%2BDryYFVrtT1DvhU6Ke1BDJe%2BsIhbxPu94NeXRBo%3D&amp;reserved=0
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> 
> I've added the patches in this series to my queue, but given what this
> one does, I think that it's a bit risky, because it exposes the kernel
> to a new category of possible platform firmware bugs.
> 

Sounds good, appreciate the diligence.

> For this reason, I'd rather queue it up as 5.16 material (and of
> course x86 reviewer comments are welcome).
> 
>> ---
>>   arch/x86/kernel/acpi/boot.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> Changes from v1 -> v2:
>>   * Make the change only apply on ACPI 6.3 or later
>> Changes from v2 -> v3:
>>   * Make acpi_support_online_capable static and only valid if CONFIG_X86_LOCAL_APIC is defined
>> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
>> index e55e0c1fad8c..d915f01b582b 100644
>> --- a/arch/x86/kernel/acpi/boot.c
>> +++ b/arch/x86/kernel/acpi/boot.c
>> @@ -62,6 +62,7 @@ int acpi_fix_pin2_polarity __initdata;
>>
>>   #ifdef CONFIG_X86_LOCAL_APIC
>>   static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
>> +static bool acpi_support_online_capable;
>>   #endif
>>
>>   #ifdef CONFIG_X86_IO_APIC
>> @@ -138,6 +139,8 @@ 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 +242,12 @@ 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
>> --
>> 2.25.1
>>