Re: [RFT PATCH v3 16/27] irqchip/apple-aic: Add support for the Apple Interrupt Controller

[Hector Martin]

On 08/03/2021 22.31, Marc Zyngier wrote:
> > +	if ((read_sysreg_s(SYS_ICH_HCR_EL2) & ICH_HCR_EN) &&
> > +		read_sysreg_s(SYS_ICH_MISR_EL2) != 0) {
> > +		pr_err("vGIC IRQ fired, disabling.\n");
>
> Please add a _ratelimited here. Whilst debugging KVM on this machine,
> I ended up with this firing at such a rate that it was impossible to
> do anything useful. Ratelimiting it allowed me to pinpoint the
> problem.

Ouch. Done for v4.

> > +static void aic_fiq_eoi(struct irq_data *d)
> > +{
> > +	/* We mask to ack (where we can), so we need to unmask at EOI. */
> > +	if (!irqd_irq_disabled(d) && !irqd_irq_masked(d))
>
> Ah, be careful here: irqd_irq_masked() doesn't do what you think it
> does for per-CPU interrupts. It's been on my list to fix for the rVIC
> implementation, but I never got around to doing it, and all decent ICs
> hide this from SW by having a HW-managed mask, similar to what is on
> the IRQ side.
>
> I can see two possibilities:
>
> - you can track the masked state directly and use that instead of
>    these predicates
>
> - you can just drop the masking altogether as this is only useful to a
>    hosted hypervisor (KVM), which will have to do its own masking
>    behind the scenes anyway

Since you're using the masking in KVM after all, I'm tracking the mask 
state in a percpu variable now. Also folded in your two minor bugfixes 
from the KVM series. Cheers!


--
Hector Martin (marcan@xxxxxxxxx)
Public Key: https://mrcn.st/pub