Messages in this thread | | | Date | Thu, 12 Aug 2021 15:45:25 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH v3 02/13] genirq: Define ack_irq() and eoi_irq() helpers |
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On Thu, 12 Aug 2021 14:36:11 +0100, Valentin Schneider <valentin.schneider@arm.com> wrote: > > On 12/08/21 08:49, Marc Zyngier wrote: > > On Tue, 29 Jun 2021 13:49:59 +0100, > > Valentin Schneider <valentin.schneider@arm.com> wrote: > >> +void eoi_irq(struct irq_desc *desc) > >> +{ > >> + desc->irq_data.chip->irq_eoi(&desc->irq_data); > >> + > >> + if (desc->irq_data.chip->flags & IRQCHIP_AUTOMASKS_FLOW) > >> + irq_state_clr_flow_masked(desc); > > > > I just realised that this has a good chance to result in a mess with > > KVM, and specially the way we let the vGIC deactivate an interrupt > > directly from the guest, without any SW intervention (the magic HW bit > > in the LRs). > > > > I didn't think to consider those. It can't ever be simple, can it... > > > With this, interrupts routed to a guest (such as the timers) will > > always have the IRQD_IRQ_FLOW_MASKED flag set, which will never be > > cleared. > > > > I wonder whether this have a chance to interact badly with > > mask/unmask, or with the rest of the flow... > > > > Isn't it the other way around? That is, eoi_irq() will clear > IRQD_IRQ_FLOW_MASKED regardless of what happens within chip->irq_eoi(), > so we would end up with !IRQD_IRQ_FLOW_MASKED even if the (physical) IRQ > remains Active (irqd_is_forwarded_to_vcpu() case).
Ah, I missed (again) that we always clear the flag, no matter what.
> This does not entirely match reality (if the IRQ is still Active then it is > still "flow-masked"), but AFAICT this doesn't impact our handling of > forwarded IRQs: IRQD_IRQ_FLOW_MASKED is only really relevant from ack_irq() > to eoi_irq(), and deactivation-from-the-guest (propagated via LR.HW=1) > happens after that.
Right. So we can have an active interrupt that is not flow-masked. That's counter-intuitive, but that's the GIC architecture for you...
I'll take the series for a ride in -next. If anything breaks, we should know pretty soon.
Thanks,
M.
-- Without deviation from the norm, progress is not possible.
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