Re: [patch 6/8] genirq: Provide IRQCHIP_AFFINITY_PRE_STARTUP

Marc Zyngier
2021-07-22T15:12:42Z

On Wed, 21 Jul 2021 20:11:32 +0100,
Thomas Gleixner <tglx@linutronix.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@linutronix.de>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Ingo Molnar <mingo@kernel.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.