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

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Date:   Fri, 28 Jul 2023 14:55:28 +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 Fri, Jul 28 2023 at 14:51, Thomas Gleixner wrote:
> 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.

In fact that function should not have a return value at all, but because
it's not clearly separated between boot time and physical hotplug, it
has to have one ...