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Date: Wed, 14 Aug 2013 14:40:41 -0400
From: Youquan Song <youquan.song@linux.intel.com>
To: Ingo Molnar <mingo@kernel.org>, Yinghai Lu <yinghai@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>, Gleb Natapov <gleb@redhat.com>,
        Youquan Song <youquan.song@intel.com>,
        Sheng Yang <sheng@linux.intel.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "H. Peter Anvin" <hpa@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        youquan.song@linux.intel.com
Subject: Re: [PATCH] x86, apic: Enable x2APIC physical when cpu < 256 native
Message-ID: <20130814184040.GA6726@linux-youquan.bj.intel.com>
References: <1373592159-459-1-git-send-email-youquan.song@intel.com> <CAE9FiQVDZGbTEd7jpmOQY9+_Gb=DRrd=CCmvQPqXWoyww2NjdQ@mail.gmail.com> <20130724062254.GA16400@redhat.com> <CAE9FiQWbVDRpLUCUTF=Jpmm-nn6kgBYFW25PPTEiPK-R-mX0jA@mail.gmail.com> <20130729170514.GB30371@linux-youquan.bj.intel.com>
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> In order to make sure the patch without involving unexpected issues beyond
> I can understand, I will confirm with our expert about it.
> 
> so please pend the patch going to mainline. If the patch can move on, I
> think I will also provide other patch changing, like direct EOI.

Hi Yinghai and Ingo,

I have confirmed with our experts about it. x2APIC without interrupt
remapping is not architecture and no guarantee it will work in future.

What's more, there are some words in SDM3, 
10.12.7 Initialization by System
Software Routing of device interrupts to local APIC units operating in
x2APIC mode requires use of the interrupt-remapping architecture
specified in the Intel Virtualization Technology for Directed I/O,
Revision 1.3. Because of this, BIOS must enumerate support for and
software must enable this interrupt remapping with Extended Interrupt
Mode Enabled before it enabling x2APIC mode in the local APIC units.

Ingo, please drop the patch in -tip tree.
3d1acb49d22fbbae96524040e9e2d4cbbb3adbef "x86/apic: Enable x2APIC
physical mode on native hardware too, when there are fewer than 256 
CPUs" 

Sorry for making fuss here and it is my fault. 

Thanks
-Youquan