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

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Date:   Wed, 8 Sep 2021 16:41:46 -0500
From:   Mario Limonciello <mario.limonciello@....com>
To:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
CC:     Mario Limonciello <mario.limonciello@....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>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "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: [PATCH v3 2/2] x86/acpi: Don't add CPUs that are not online capable

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://uefi.org/htmlspecs/ACPI_Spec_6_4_html/05_ACPI_Software_Programming_Model/ACPI_Software_Programming_Model.html?#local-apic-flags
Signed-off-by: Mario Limonciello <mario.limonciello@....com>
---
 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