[PATCH v2] x86/acpi/boot: Do not register processors that cannot be onlined for x2apic

Kishon Vijay Abraham I
2023-01-05T04:12:16Z

Section 5.2.12.12 Processor Local x2APIC Structure in the ACPI v6.5
spec mandates that both "enabled" and "online capable" Local APIC Flags
should be used to determine if the processor is usable or not.

However, Linux doesn't use the "online capable" flag for x2APIC to
determine if the processor is usable. As a result, cpu_possible_mask has
incorrect value and results in more memory getting allocated for per_cpu
variables than it is going to be used.

Make sure Linux parses both "enabled" and "online capable" flags for
x2APIC to correctly determine if the processor is usable.

Fixes: aa06e20f1be6 ("x86/ACPI: Don't add CPUs that are not online capable")
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reported-by: Leo Duran <leo.duran@amd.com>
Signed-off-by: Kishon Vijay Abraham I <kvijayab@amd.com>
---
Changes from v1:
1) Changed the ACPI spec version to 6.5 in the commit log
2) Changed the Fixes tag to point to commit aa06e20f1be6
3) Added "Reported-by: Leo Duran <leo.duran@amd.com>"
arch/x86/kernel/acpi/boot.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 907cc98b1938..518bda50068c 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -188,6 +188,17 @@ static int acpi_register_lapic(int id, u32 acpiid, u8 enabled)
return cpu;
}

+static bool __init acpi_is_processor_usable(u32 lapic_flags)
+{
+ if (lapic_flags & ACPI_MADT_ENABLED)
+ return true;
+
+ if (acpi_support_online_capable && (lapic_flags & ACPI_MADT_ONLINE_CAPABLE))
+ return true;
+
+ return false;
+}
+
static int __init
acpi_parse_x2apic(union acpi_subtable_headers *header, const unsigned long end)
{
@@ -212,6 +223,10 @@ acpi_parse_x2apic(union acpi_subtable_headers *header, const unsigned long end)
if (apic_id == 0xffffffff)
return 0;

+ /* don't register processors that cannot be onlined */
+ if (!acpi_is_processor_usable(processor->lapic_flags))
+ return 0;
+
/*
* We need to register disabled CPU as well to permit
* counting disabled CPUs. This allows us to size
@@ -250,9 +265,7 @@ acpi_parse_lapic(union acpi_subtable_headers * header, const unsigned long end)
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))
+ if (!acpi_is_processor_usable(processor->lapic_flags))
return 0;

/*
--
2.34.1