[tip: x86/boot] x86/acpi/boot: Do not register processors that cannot be onlined for x2APIC

[tip-bot2 for Kishon Vijay Abraham I]

The following commit has been merged into the x86/boot branch of tip:

Commit-ID:     e2869bd7af608c343988429ceb1c2fe99644a01f
Gitweb:        https://git.kernel.org/tip/e2869bd7af608c343988429ceb1c2fe99644a01f
Author:        Kishon Vijay Abraham I <kvijayab@xxxxxxx>
AuthorDate:    Thu, 05 Jan 2023 04:10:59 
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Tue, 10 Jan 2023 19:21:07 +01:00

x86/acpi/boot: Do not register processors that cannot be onlined for x2APIC

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")
Reported-by: Leo Duran <leo.duran@xxxxxxx>
Signed-off-by: Kishon Vijay Abraham I <kvijayab@xxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Zhang Rui <rui.zhang@xxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Link: https://lore.kernel.org/r/20230105041059.39366-1-kvijayab@xxxxxxx
---
 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 907cc98..518bda5 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;
 
 	/*