linux-kernel - Re: [PATCH] irqchip/gic-v3-its: Don't try to move a disabled irq

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Message-ID: <8c3be990888ecfb7cca9503853dc4aac@kernel.org>
Date:   Fri, 29 May 2020 09:32:33 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Ali Saidi <alisaidi@...zon.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        benh@...zon.com, dwmw@...zon.com, zeev@...zon.com, zorik@...zon.com
Subject: Re: [PATCH] irqchip/gic-v3-its: Don't try to move a disabled irq

Hi Ali,

On 2020-05-29 02:55, Ali Saidi wrote:
> If an interrupt is disabled the ITS driver has sent a discard removing
> the DeviceID and EventID from the ITT. After this occurs it can't be
> moved to another collection with a MOVI and a command error occurs if
> attempted. Before issuing the MOVI command make sure that the IRQ isn't
> disabled and change the activate code to try and use the previous
> affinity.
> 
> Signed-off-by: Ali Saidi <alisaidi@...zon.com>
> ---
>  drivers/irqchip/irq-gic-v3-its.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c 
> b/drivers/irqchip/irq-gic-v3-its.c
> index 124251b0ccba..1235dd9a2fb2 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -1540,7 +1540,11 @@ static int its_set_affinity(struct irq_data *d,
> const struct cpumask *mask_val,
>  	/* don't set the affinity when the target cpu is same as current one 
> */
>  	if (cpu != its_dev->event_map.col_map[id]) {
>  		target_col = &its_dev->its->collections[cpu];
> -		its_send_movi(its_dev, target_col, id);
> +
> +		/* If the IRQ is disabled a discard was sent so don't move */
> +		if (!irqd_irq_disabled(d))
> +			its_send_movi(its_dev, target_col, id);
> +

This looks wrong. What you are testing here is whether the interrupt
is masked, not that there isn't a valid translation.

In the commit message, you're saying that we've issued a discard. This
hints at doing a set_affinity on an interrupt that has been deactivated
(mapping removed). Is that actually the case? If so, why was it 
deactivated
the first place?

>  		its_dev->event_map.col_map[id] = cpu;
>  		irq_data_update_effective_affinity(d, cpumask_of(cpu));
>  	}
> @@ -3439,8 +3443,16 @@ static int its_irq_domain_activate(struct
> irq_domain *domain,
>  	if (its_dev->its->numa_node >= 0)
>  		cpu_mask = cpumask_of_node(its_dev->its->numa_node);
> 
> -	/* Bind the LPI to the first possible CPU */
> -	cpu = cpumask_first_and(cpu_mask, cpu_online_mask);
> +	/* If the cpu set to a different CPU that is still online use it */
> +	cpu = its_dev->event_map.col_map[event];
> +
> +	cpumask_and(cpu_mask, cpu_mask, cpu_online_mask);
> +
> +	if (!cpumask_test_cpu(cpu, cpu_mask)) {
> +		/* Bind the LPI to the first possible CPU */
> +		cpu = cpumask_first(cpu_mask);
> +	}
> +
>  	if (cpu >= nr_cpu_ids) {
>  		if (its_dev->its->flags & ITS_FLAGS_WORKAROUND_CAVIUM_23144)
>  			return -EINVAL;

So you deactivate an interrupt, do a set_affinity that doesn't issue
a MOVI but preserves the affinity, then reactivate it and hope that
the new mapping will target the "right" CPU.

That seems a bit mad, but I presume this isn't the whole story...

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...