linux-kernel - Re: [RFC 4/6] x86, NMI, Rewrite NMI handler

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Message-ID: <20100910182952.GJ4879@redhat.com>
Date:	Fri, 10 Sep 2010 14:29:52 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Huang Ying <ying.huang@...el.com>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC 4/6] x86, NMI, Rewrite NMI handler

On Fri, Sep 10, 2010 at 06:03:56PM +0200, Andi Kleen wrote:
> On Fri, 10 Sep 2010 11:56:05 -0400
> Don Zickus <dzickus@...hat.com> wrote:
> 
> > On Fri, Sep 10, 2010 at 10:51:03AM +0800, Huang Ying wrote:
> > > The original NMI handler is quite outdated in many aspects. This
> > > patch try to fix it.
> > > 
> > > In original code, NMI reason io port (0x61) is only processed on
> > > BSP. This makes it impossible to hot-remove BSP. To solve the issue,
> > > a raw spinlock is used to make the port can be processed on any CPU.
> > 
> > Do we really want to use a spinlock inside the nmi handler?
> 
> As long as it's only between CPUs
> (that is only ever used between different NMI handlers) 
> that's fine.  It's certainly safer than having races between CPUs.
> 
> > I thought the NMIs sent to the io port are only routed to one cpu as
> > determined by the io-apic?  Is it spread out to other cpus now?
> 
> There can be cases where it can happen I believe.

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?

Cheers,
Don
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