linux-kernel - Re: [tip:x86/apic] x86/acpi: Introduce persistent storage for cpuid <-> apicid mapping

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Date:   Fri, 7 Oct 2016 11:55:39 -0700
From:   Yinghai Lu <yinghai@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Dou Liyang <douly.fnst@...fujitsu.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>,
        Tony Luck <tony.luck@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "Zheng, Lv" <lv.zheng@...el.com>,
        Bob Moore <robert.moore@...el.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [tip:x86/apic] x86/acpi: Introduce persistent storage for cpuid
 <-> apicid mapping

On Fri, Oct 7, 2016 at 6:00 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Fri, 7 Oct 2016, Thomas Gleixner wrote:
>> On Fri, 7 Oct 2016, Dou Liyang wrote:
>> > Is it possible that the "-1/oxffffffff" could appear in the MADT which is one
>> > of the ACPI tables?
>>
>> According to the SDM the x2apic id is a 32bit ID, so 0xffffffff is a
>> legitimate value.
>
> The ACPI spec says that bit 0 of the x2apic flags field tells whether the
> logical processor is present or not. So the proper check for x2apic is that
> flag.
>
> The lapic structure has the same flag, but the kernel ignores the flags for
> both lapic and x2apic.
>
> I'm going to apply the minimal fix of checking for id == 0xff in
> acpi_lapic_parse() for now, but this needs to be revisited and fixed
> proper.

Good to me. Thanks for fixing it.

Yinghai