linux-kernel - Re: [PATCH -v8] x86: Disable x2apic if nox2apic is specified or intr-remap can not be enabled

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Date:	Fri, 16 Dec 2011 18:07:03 -0800
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -v8] x86: Disable x2apic if nox2apic is specified or
 intr-remap can not be enabled

On Fri, 2011-12-16 at 16:59 -0800, Yinghai Lu wrote:
> For
> 1. x2apic preenabled system
> 2. first kernel have x2apic enabled, and try to kexec second kernel with "nox2apic"
> 
> Will put back cpu with apic id < 255 into xapic mode, instead of panic.
> 

Yinghai, I didn't get a chance to review this patch completely. But few
things.

a. Need to split this patch into multiple patches, specially the cpuid
mechanism to get the initial apic id, flat_probe etc. While I understand
the reason behind the flat_probe change, it isn't quite obvious from
this changelog.

b. for nox2apic, as you try to disable x2apic even if the bios has
enabled it along with interrupt-remapping, this will probably not work
unless we disable interrupt-remapping. So either we need to ignore the
nox2apic when OS can find that interrupt-remapping is already enabled or
disable interrupt-remapping. Let me think a bit more about this and get
back to you by monday with detailed review of this.

thanks,
suresh

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