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

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Date:   Fri, 26 Mar 2021 16:57:29 +0900
From:   Hector Martin <marcan@...can.st>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Rob Herring <robh@...nel.org>, Arnd Bergmann <arnd@...nel.org>,
        Olof Johansson <olof@...om.net>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Tony Lindgren <tony@...mide.com>,
        Mohamed Mediouni <mohamed.mediouni@...amail.com>,
        Stan Skowronek <stan@...ellium.com>,
        Alexander Graf <graf@...zon.com>,
        Will Deacon <will@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Christoph Hellwig <hch@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        devicetree@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFT PATCH v3 16/27] irqchip/apple-aic: Add support for the Apple
 Interrupt Controller

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@...can.st)
Public Key: https://mrcn.st/pub