linux-kernel - Re: [PATCH] genirq/msi: Shutdown managed interrupts with unsatifiable affinities

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Date:   Mon, 7 Mar 2022 17:34:12 -0800
From:   David Decotigny <ddecotig@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Garry <john.garry@...wei.com>
Subject: Re: [PATCH] genirq/msi: Shutdown managed interrupts with unsatifiable affinities

On Mon, Mar 7, 2022 at 11:06 AM Marc Zyngier <maz@...nel.org> wrote:
>
> When booting with maxcpus=<small number>, interrupt controllers
> such as the GICv3 ITS may not be able to satisfy the affinity of
> some managed interrupts, as some of the HW resources are simply
> not available.
>
> In order to deal with this, do not try to activate such interrupt
> if there is no online CPU capable of handling it. Instead, place
> it in shutdown state. Once a capable CPU shows up, it will be
> activated.
>
> Reported-by: John Garry <john.garry@...wei.com>
> Reported-by: David Decotigny <ddecotig@...gle.com>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> ---
>  kernel/irq/msi.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
> index 2bdfce5edafd..aa84ce84c2ec 100644
> --- a/kernel/irq/msi.c
> +++ b/kernel/irq/msi.c
> @@ -818,6 +818,18 @@ static int msi_init_virq(struct irq_domain *domain, int virq, unsigned int vflag
>                 irqd_clr_can_reserve(irqd);
>                 if (vflags & VIRQ_NOMASK_QUIRK)
>                         irqd_set_msi_nomask_quirk(irqd);
> +
> +               /*
> +                * If the interrupt is managed but no CPU is available
> +                * to service it, shut it down until better times.
> +                */
> +               if ((vflags & VIRQ_ACTIVATE) &&
> +                   irqd_affinity_is_managed(irqd) &&
> +                   !cpumask_intersects(irq_data_get_affinity_mask(irqd),
> +                                       cpu_online_mask)) {
> +                           irqd_set_managed_shutdown(irqd);
> +                           return 0;
> +                   }
>         }
>
>         if (!(vflags & VIRQ_ACTIVATE))
> --
> 2.30.2
>

Thanks! I tried that patch, and it worked for us.