Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [PATCH v3 02/13] genirq: Define ack_irq() and eoi_irq() helpers | Date | Thu, 12 Aug 2021 14:36:11 +0100 |
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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).
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.
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