Re: [Xen-devel] [PATCH 2/5] xen/arm: Keep count of inflight interrupts

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-06-25 at 19:38 +0100, Stefano Stabellini wrote:
> > > If that is the case, this can only happen once, right?  In that case
> > > rather than an atomic_t we could just have a bit in the status field I
> > > proposed before. It should be enough for us to keep track of the case
> > > when the irq is supposed to stay high even after the guest EOIs it. (Of
> > > course that means that we need to re-inject it into the guest).
> > 
> > 
> > For the timer yes. I wonder, what happen if Xen receive an SGI (for
> > instance SCHEDULE ipi) twice, does Xen must re-inject it multiple times?
> 
> I don't think it can happen with anything but the vtimer: in order for
> the scenario above to happen it takes an irq that is EOId in the
> hardware before the guest EOIs it.
> 
> SGIs are completely "emulated", there is not an hardware irq
> corresponding to them. From the Xen point of view the SGI is inflight
> exactly and only from the moment the first vcpu sends it, to the point
> when the receiving vcpu EOIs it.

Are we talking about real SGIs (passed by Xen between physical
processors) or fake SGIs (emulated between virtual processors)?

Ian.



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