[Xen-devel] Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking

[Don Zickus <dzickus@xxxxxxxxxx>]

On Tue, Sep 13, 2011 at 09:58:38PM +0200, Andi Kleen wrote:
> > Or are you saying an NMI in an idle system will have the same %rip thus
> > falsely detecting a back-to-back NMI?
> 
> Yup.

Hmm.  That sucks.  Is there another register that can be used in
conjunction to seperate it, like sp or something?  Or we can we assume
than an idle cpu isn't doing much for local NMI IPIs and that the only
NMIs that would interrupt it would be external ones?

> 
> Another problem is very long running instructions, like WBINVD and some 
> others.
> If there's a high frequency NMI it may well hit multiple times in a single
>  instance.

I thought NMIs happen on instruction boundaries, maybe not.

Honestly, our current implementation would probably be tripped up with
those examples too, so I don't think I am making things worse (assuming
the only high frequency NMI is coming from perf).

Cheers,
Don

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