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SubjectRe: [PATCH v3 1/1] ppc/crash: Reset spinlocks during crash
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On Wed, 2020-04-08 at 22:21 +1000, Michael Ellerman wrote:
[...]
> > On the other hand, busting the rtas.lock could be dangerous, because
> > it's code we can't control.
> >
> > According with LoPAR, for both of these rtas-calls, we have:
> >
> > For the PowerPC External Interrupt option: The call must be reentrant
> > to the number of processors on the platform.
> > For the PowerPC External Interrupt option: The argument call buffer for
> > each simultaneous call must be physically unique.
>
> Oh well spotted. Where is that in the doc?

In the current LoPAR available on OpenPower Foundation, it's on page
170, '7.3.10.2 ibm,set-xive' and '7.3.10.3 ibm,int-off'.

> > Which I think means this rtas-calls can be done simultaneously.
>
> I think so too. I'll read PAPR in the morning and make sure.
>
> > Would it mean that busting the rtas.lock for these calls would be safe?
>
> What would be better is to make those specific calls not take the global
> RTAS lock to begin with.
>
> We should be able to just allocate the rtas_args on the stack, it's only
> ~80 odd bytes. And then we can use rtas_call_unlocked() which doesn't
> take the global lock.

Good idea. I will try getting some work done on this.

Best regards,
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