From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751929Ab0INNiV (ORCPT ); Tue, 14 Sep 2010 09:38:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:27756 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751616Ab0INNiS (ORCPT ); Tue, 14 Sep 2010 09:38:18 -0400 Date: Tue, 14 Sep 2010 09:37:56 -0400 From: Don Zickus To: Huang Ying Cc: Andi Kleen , Ingo Molnar , "H. Peter Anvin" , "linux-kernel@vger.kernel.org" Subject: Re: [RFC 4/6] x86, NMI, Rewrite NMI handler Message-ID: <20100914133756.GI26290@redhat.com> References: <1284087065-32722-1-git-send-email-ying.huang@intel.com> <1284087065-32722-4-git-send-email-ying.huang@intel.com> <20100910155605.GG4879@redhat.com> <20100910180356.44ac7097@basil.nowhere.org> <20100910182952.GJ4879@redhat.com> <1284343770.3269.75.camel@yhuang-dev.sh.intel.com> <20100913140419.GA27371@redhat.com> <1284441161.2256.94.camel@yhuang-dev.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1284441161.2256.94.camel@yhuang-dev.sh.intel.com> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 14, 2010 at 01:12:41PM +0800, Huang Ying wrote: > On Mon, 2010-09-13 at 22:04 +0800, Don Zickus wrote: > > On Mon, Sep 13, 2010 at 10:09:30AM +0800, Huang Ying wrote: > > > > The reason I asked was, I thought it would be easier to have a global > > > > variable that tells the nmi handler which cpu has the NMI's routed to its > > > > io port. This way if you want to swap out the bsp cpu, you could perhaps > > > > just re-route the nmi to a new cpu and the global variable would be > > > > updated accordingly? > > > > > > Then we need some kind of protection or race condition between > > > re-routing NMI and updating the variable. Do you think so? > > > > Well, I thought the only reasonable place to update the variable is when > > the cpu is being taken offline, during the MTRR update. Since no NMIs can > > be processed when the cpu's are syncing their MTRR, there shouldn't be a > > race condition, no? > > > > Then again I am probably missing something obvious. Like I don't know how > > cpu's deal with interrupts/NMIs when they are going offline. > > > > It was just a thought to avoid the spinlock. > > Why do you hate spinlock inside NMI handler? I think it is safe and > simple if only used in NMI handler. I guess I always had the mentality that spinlocks in an NMI context was a big no-no. Never really thought about if there were safe use-cases or not. Cheers, Don