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

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Message-ID: <8c52c038-3c7d-748f-d4d0-fa021f6530dc@cn.fujitsu.com>
Date:   Sat, 8 Oct 2016 13:22:56 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Yinghai Lu <yinghai@...nel.org>,
        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>, <robert.moore@...el.com>,
        <linux-acpi@...r.kernel.org>
Subject: Re: [tip:x86/apic] x86/acpi: Introduce persistent storage for cpuid
 <-> apicid mapping

Hi tglx,

At 10/07/2016 09:00 PM, Thomas Gleixner 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.

Yes, I see.

>
> 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.

It seems the kernel uses the flags in this sentence:

	enabled = processor->lapic_flags & ACPI_MADT_ENABLED;


>
> 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.

Yes, I will do it.


Thanks

	Dou.