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

Huang Ying
2010-09-14T05:12:48Z

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.

Best Regards,
Huang Ying