Re: [Xen-devel] [PATCH v5] xen/arm: trap guest WFI

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 19 Apr 2013, Ian Campbell wrote:
> > > >  }
> > > >  
> > > >  static inline void local_event_delivery_enable(void)
> > > 
> > > This one is called from do_block in common code but if the guest never
> > > sets this then it seems a bit pointless. Perhaps this should be
> > > manipulating CPSR_I instead?
> > 
> > I think it's fine to keep it as it is because in the future a guest on
> > ARM might decide to use it and I think it's an interface that we should
> > support.
> 
> No it isn't, it is a piece of PV legacy which introduces difficult to
> solve races (all that critical section stuff) on the event re-enable
> path. There is no reason at all to use it when you have proper
> virtualised interrupt mask functionality in the hardware.

evtchn_upcall_mask is part of struct vcpu_info that is defined in
xen/include/public/xen.h, that is an arch-independent public header.

So yes, it is part of the interface that we support.

I fail to see an easy way to remove it from it, we can't just add a
comment say "please don't use it".
I wouldn't be happy with ifdef'ing it out because I would rather keep
this interface arch-independent. However I do see an easy way to support
it on ARM.

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