linux-kernel - Re: [patch 6/8] genirq: Provide IRQCHIP_AFFINITY_PRE

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Date:   Thu, 22 Jul 2021 16:12:19 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Raj, Ashok" <ashok.raj@...el.com>, Ingo Molnar <mingo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        Kevin Tian <kevin.tian@...el.com>, x86@...nel.org
Subject: Re: [patch 6/8] genirq: Provide IRQCHIP_AFFINITY_PRE_STARTUP

On Wed, 21 Jul 2021 20:11:32 +0100,
Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> X86 IO/APIC and MSI interrupts (when used without interrupts remapping)
> require that the affinity setup on startup is done before the interrupt is
> enabled for the first time as the non-remapped operation mode cannot safely
> migrate enabled interrupts from arbitrary contexts. Provide a new irq chip
> flag which allows affected hardware to request this.
> 
> This has to be opt-in because there have been reports in the past that some
> interrupt chips cannot handle affinity setting before startup.
> 
> Fixes: 18404756765c ("genirq: Expose default irq affinity mask (take 3)")
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> ---
>  include/linux/irq.h |    2 ++
>  kernel/irq/chip.c   |    5 ++++-
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> --- a/include/linux/irq.h
> +++ b/include/linux/irq.h
> @@ -569,6 +569,7 @@ struct irq_chip {
>   * IRQCHIP_SUPPORTS_NMI:              Chip can deliver NMIs, only for root irqchips
>   * IRQCHIP_ENABLE_WAKEUP_ON_SUSPEND:  Invokes __enable_irq()/__disable_irq() for wake irqs
>   *                                    in the suspend path if they are in disabled state
> + * IRQCHIP_AFFINITY_PRE_STARTUP:      Default affinity update before startup
>   */
>  enum {
>  	IRQCHIP_SET_TYPE_MASKED			= (1 <<  0),
> @@ -581,6 +582,7 @@ enum {
>  	IRQCHIP_SUPPORTS_LEVEL_MSI		= (1 <<  7),
>  	IRQCHIP_SUPPORTS_NMI			= (1 <<  8),
>  	IRQCHIP_ENABLE_WAKEUP_ON_SUSPEND	= (1 <<  9),
> +	IRQCHIP_AFFINITY_PRE_STARTUP		= (1 << 10),
>  };
>  
>  #include <linux/irqdesc.h>
> --- a/kernel/irq/chip.c
> +++ b/kernel/irq/chip.c
> @@ -265,8 +265,11 @@ int irq_startup(struct irq_desc *desc, b
>  	} else {
>  		switch (__irq_startup_managed(desc, aff, force)) {
>  		case IRQ_STARTUP_NORMAL:
> +			if (d->chip->flags & IRQCHIP_AFFINITY_PRE_STARTUP)
> +				irq_setup_affinity(desc);

How about moving this to activate instead? We already special-case the
activation of MSIs for PCI (MSI_FLAG_ACTIVATE_EARLY), and this
wouldn't look completely out of place. The startup mode could be an
issue though...

>  			ret = __irq_startup(desc);
> -			irq_setup_affinity(desc);
> +			if (!(d->chip->flags & IRQCHIP_AFFINITY_PRE_STARTUP))
> +				irq_setup_affinity(desc);
>  			break;
>  		case IRQ_STARTUP_MANAGED:
>  			irq_do_set_affinity(d, aff, false);

Otherwise, looks good.

	M.

-- 
Without deviation from the norm, progress is not possible.