linux-kernel - Re: [PATCH] Use x2apic_supported() in the default_apic_id

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Message-ID: <CAE9FiQUtf9Pix3rmhgk_+oOf19dOvvgQYt+gbHQyag0xkH_bxA@mail.gmail.com>
Date:	Thu, 15 Mar 2012 21:19:35 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Steffen Persvold <sp@...ascale.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Daniel J Blueman <daniel@...ascale-asia.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] Use x2apic_supported() in the default_apic_id_valid() function.

On Thu, Mar 15, 2012 at 7:08 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>> So this change breaks the commit
>> c284b42abadbb22083bfde24d308899c08d44ffa.
>>
>> I think the right thing is to have two different apid_id_valid checks
>> one for xapic driver (apic_flat_64.c) and another for x2apic driver
>> (x2apic_phys/cluster.c) and that way, x2apic MADT entries will be parsed
>> only if bios has handed over the OS in x2apic mode or if we have
>> selected the numachip model.
>
> that looks like more clear.

after more thinking, I think We should still use cpu_has_x2apic checking.

one maybe invalid case:

System have some cpus apic id < 255, and some cpu apic id > 255.
BSP apic id < 255.
those cpus apic id < 255 will be put into xapic mode, cpus > 255 will
be put into x2apic mode.
and DMAR table intr-remapping will be working.

So if we check x2apic_mode early, will skip cpu with apic id > 255,
even switch to x2apic later.

Thanks

Yinghai Lu
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