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Subject: Re: [tip:x86/apic] x86/acpi: Introduce persistent storage for cpuid
 <-> apicid mapping
To: Thomas Gleixner <tglx@linutronix.de>
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From: Dou Liyang <douly.fnst@cn.fujitsu.com>
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Date: Sat, 8 Oct 2016 13:22:56 +0800
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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.