linux-kernel - Re: [RFC PATCH] x86/acpi: Ignore invalid x2APIC entries

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Date:   Fri, 28 Jul 2023 14:51:48 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Zhang Rui <rui.zhang@...el.com>, peterz@...radead.org,
        bp@...en8.de, rafael.j.wysocki@...el.com
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        x86@...nel.org, feng.tang@...el.com
Subject: Re: [RFC PATCH] x86/acpi: Ignore invalid x2APIC entries

On Mon, Jul 03 2023 at 00:28, Zhang Rui wrote:
>  
> +static bool has_lapic_cpus;

Yet another random flag. Sigh.

I really hate this. Why not doing the obvious?

--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2452,6 +2452,9 @@ int generic_processor_info(int apicid, i
 	bool boot_cpu_detected = physid_isset(boot_cpu_physical_apicid,
 				phys_cpu_present_map);
 
+	if (physid_isset(apicid, phys_cpu_present_map))
+		return -EBUSY;
+
 	/*
 	 * boot_cpu_physical_apicid is designed to have the apicid
 	 * returned by read_apic_id(), i.e, the apicid of the

As the call sites during MADT parsing ignore the return value anyway,
there is no harm and this is a proper defense against broken tables
which enumerate an APIC twice.

Thanks,

        tglx