Re: Recoverable MCA interrupts from NMI handlers? IPMI and RCU?

[H. Peter Anvin]

Paul E. McKenney wrote:
> Hello!
>
> A couple of questions about the x86 architecture...
>
> 1.	Can recoverable machine-check exceptions occur from within
> 	NMI handlers?  If so, there is a bug in preemptable RCU's
> 	CONFIG_NO_HZ handling that could be fixed by a patch something
> 	like the one shown below (untested, probably does not even
> 	compile).

In theory, recoverable #MC's can occur anywhere.  It's an exception.

> 2.	Does the IPMI subsystem make use of RCU read-side primitives
> 	from within SMI handlers?  If so, we need the SMI handlers to
> 	invoke rcu_irq_enter() upon entry and rcu_irq_exit() upon exit
> 	when they are invoked from dynticks idle state.  Or something
> 	similar, depending on restrictions on code within SMI handlers.

Not sure about that one.  I clearly need to look carefully into this... 
SMI is quite "special" in that it sets up an entirely new environment; 
the concept of executing kernel code at SMI level makes me want to run 
away and hide.

	-hpa

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