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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Marc Zyngier <maz@kernel.org>, linux-kernel@vger.kernel.org
Cc:     John Garry <john.garry@huawei.com>,
        David Decotigny <ddecotig@google.com>
Subject: Re: [PATCH] genirq/msi: Shutdown managed interrupts with
 unsatifiable affinities
In-Reply-To: <20220307190625.254426-1-maz@kernel.org>
References: <20220307190625.254426-1-maz@kernel.org>
Date:   Mon, 14 Mar 2022 16:27:10 +0100
Message-ID: <87sfrkftbl.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Mon, Mar 07 2022 at 19:06, Marc Zyngier 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.

This is also true if you have offlined lots of CPUs, right?

> 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@huawei.com>
> Reported-by: David Decotigny <ddecotig@google.com>
> Signed-off-by: Marc Zyngier <maz@kernel.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);

Hrm. Why is this in the !CAN_RESERVE path and not before the actual
activation call?

Thanks,

        tglx