Re: [patch, 2.6.10-rc3] safe_hlt() & NMIs

[Ingo Molnar]

* Maciej W. Rozycki <macro@xxxxxxxxxxxxxx> wrote:

> On Thu, 16 Dec 2004, Ingo Molnar wrote:
> 
> > c0125ee9:     1529 	fa                   	cli    
> >                  ^---------------------------------- # of profiler hits
> > c0125eea:      507 	fb                   	sti    
> > c0125eeb:        0 	fa                   	cli    
> > c0125eec:     3719 	fb                   	sti    
> > c0125eed:        0 	fa                   	cli    
> > c0125eee:     1579 	fb                   	sti    
> > c0125eef:        0 	fa                   	cli    
> > c0125ef0:     3317 	fb                   	sti    
> > c0125ef1:        0 	fa                   	cli    
> > c0125ef2:     3030 	fb                   	sti    
> > c0125ef3:        0 	fa                   	cli    
> > c0125ef4:     2497 	fa                   	cli    
> > c0125ef5:     1055 	fb                   	sti    
> > c0125ef6:        0 	fa                   	cli    
> [...]
> > the 'cli' is always a 'black hole' to the NMI, while the second of two
> > consecutive cli's are not.
> 
>  It looks like the 'sti' is actually the black hole -- remember
> interrupts are traps, that is they are probed for and taken after
> instruction execution.

The 'sti' "shadows" the cli, i.e. we'll never get an interrupt that gets
inbetween 'sti;cli'. I.e. sti is the black-hole generator, and 'cli' is
in the black hole. In that sense the 'cli' is in a black hole to the
NMI: the NMI will never see cli as the 'next to be executed'
instruction.

	Ingo
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