Re: [Xen-devel] [PATCH-4.5 4/4] xen/arm: set GICH_HCR_NPIE if all the LRs are in use

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 7 Feb 2014, Julien Grall wrote:
> On 07/02/14 18:56, Stefano Stabellini wrote:
> > On return to guest, if there are no free LRs and we still have more
> > interrupt to inject, set GICH_HCR_NPIE so that we are going to receive a
> > maintenance interrupt when no pending interrupts are present in the LR
> > registers.
> > The maintenance interrupt handler won't do anything anymore, but
> > receiving the interrupt is going to cause gic_inject to be called on
> > return to guest that is going to clear the old LRs and inject new
> > interrupts.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > ---
> >   xen/arch/arm/gic.c |    8 +++++++-
> >   1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
> > index 87bd5d3..bee2618 100644
> > --- a/xen/arch/arm/gic.c
> > +++ b/xen/arch/arm/gic.c
> > @@ -810,8 +810,14 @@ void gic_inject(void)
> >       gic_restore_pending_irqs(current);
> >       if (!gic_events_need_delivery())
> >           gic_inject_irq_stop();
> > -    else
> > +    else {
> >           gic_inject_irq_start();
> > +    }
> > +
> > +    if ( !list_empty(&current->arch.vgic.lr_pending) )
> > +        GICH[GICH_HCR] = GICH_HCR_EN | GICH_HCR_NPIE;
> > +    else
> > +        GICH[GICH_HCR] = GICH_HCR_EN;
> 
> Any reason to not move this in the else?

Yes: we need to be able to disable GICH_HCR_NPIE even if there are no
irqs to inject.


> BTW, I think we can safely avoid to reinject the IRQ for the event channels if
> there is pending events. It will also avoid spurious IRQ on some specific case
> :).

Currently we don't set GIC_IRQ_GUEST_PENDING for evtchn_irq if the irq
is already inflight. I'll see if I can come up with a patch to
streamline that behaviour.

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