From: Dou Liyang <douly.fnst@cn.fujitsu.com>
Date: Thu, 12 Apr 2018 09:40:52 +0800
Subject: x86/acpi: Prevent X2APIC id 0xffffffff from being accounted
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Git-commit: 10daf10ab154e31237a8c07242be3063fb6a9bf4
Patch-mainline: v4.17-rc2
References: bsc#1110006

RongQing reported that there are some X2APIC id 0xffffffff in his machine's
ACPI MADT table, which makes the number of possible CPU inaccurate.

The reason is that the ACPI X2APIC parser has no sanity check for APIC ID
0xffffffff, which is an invalid id in all APIC types. See "Intel® 64
Architecture x2APIC Specification", Chapter 2.4.1.

Add a sanity check to acpi_parse_x2apic() which ignores the invalid id.

Reported-by: Li RongQing <lirongqing@baidu.com>
Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Cc: len.brown@intel.com
Cc: rjw@rjwysocki.net
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/20180412014052.25186-1-douly.fnst@cn.fujitsu.com

Acked-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/kernel/acpi/boot.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -211,6 +211,11 @@ acpi_parse_x2apic(struct acpi_subtable_h
 
 	apic_id = processor->local_apic_id;
 	enabled = processor->lapic_flags & ACPI_MADT_ENABLED;
+
+	/* Ignore invalid ID */
+	if (apic_id == 0xffffffff)
+		return 0;
+
 #ifdef CONFIG_X86_X2APIC
 	/*
 	 * We need to register disabled CPU as well to permit