[RFC PATCH v2 45/45] irqchip/gic-v5: Add NMI support for IPIs

[Marc Zyngier]

On Mon, 27 Jul 2026 17:34:53 +0100,
Vladimir Murzin <vladimir.murzin at arm.com> wrote:
> 
> IPIs are implemented as a logical domain on top of the LPI domain.
> Therefore, when an IPI is configured as an NMI, update the priority in
> the parent LPI domain during setup and teardown.
> 
> Permit irq_supports_nmi() to accept IRQs managed by an NMI-capable
> parent domain.
> 
> Finally, guard handle_irq_event_percpu() against calling
> add_interrupt_randomness() from NMI context.
> 
> Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
> ---
>  drivers/irqchip/irq-gic-v5.c | 23 ++++++++++++++++++++++-
>  kernel/irq/handle.c          |  3 ++-
>  kernel/irq/manage.c          | 11 ++++++++---
>  3 files changed, 32 insertions(+), 5 deletions(-)
> 
> The patch should definitely be split. The only reason I'm keeping it
> as a single patch for now is that I'm not yet sure these changes are
> moving in the right direction...
> 
> 
> diff --git a/drivers/irqchip/irq-gic-v5.c b/drivers/irqchip/irq-gic-v5.c
> index 05b957ffc0b8..787cb8da4e1a 100644
> --- a/drivers/irqchip/irq-gic-v5.c
> +++ b/drivers/irqchip/irq-gic-v5.c
> @@ -700,6 +700,24 @@ static void gicv5_spi_irq_nmi_teardown(struct irq_data *d)
>  	irq_to_desc(d->irq)->handle_irq = handle_fasteoi_irq;
>  }
>  
> +static int gicv5_ipi_irq_nmi_setup(struct irq_data *d)
> +{
> +	if (WARN_ON(!d->parent_data))
> +		return -EINVAL;

How can this happen? Shouldn't that be impossible by construction?

> +
> +	d = d->parent_data;
> +
> +	return gicv5_hwirq_irq_nmi_setup(d->hwirq, GICV5_HWIRQ_TYPE_LPI);
> +}
> +
> +static void gicv5_ipi_irq_nmi_teardown(struct irq_data *d)
> +{
> +	if (WARN_ON(!d->parent_data))
> +		return;
> +
> +	d = d->parent_data;
> +
> +	gicv5_hwirq_irq_nmi_teardown(d->hwirq, GICV5_HWIRQ_TYPE_LPI);
>  }
>  
>  static struct irq_chip gicv5_ppi_irq_chip = {
> @@ -749,7 +767,7 @@ static struct irq_chip gicv5_lpi_irq_chip = {
>  				  IRQCHIP_MASK_ON_SUSPEND,
>  };
>  
> -static const struct irq_chip gicv5_ipi_irq_chip = {
> +static struct irq_chip gicv5_ipi_irq_chip = {

If we can't have it const, can we have it as __ro_after_init?

>  	.name			= "GICv5-IPI",
>  	.irq_mask		= irq_chip_mask_parent,
>  	.irq_unmask		= irq_chip_unmask_parent,
> @@ -757,6 +775,8 @@ static const struct irq_chip gicv5_ipi_irq_chip = {
>  	.irq_set_affinity	= irq_chip_set_affinity_parent,
>  	.irq_get_irqchip_state	= irq_chip_get_parent_state,
>  	.irq_set_irqchip_state	= irq_chip_set_parent_state,
> +	.irq_nmi_setup		= gicv5_ipi_irq_nmi_setup,
> +	.irq_nmi_teardown	= gicv5_ipi_irq_nmi_teardown,
>  	.ipi_send_single	= gicv5_ipi_send_single,
>  	.flags			= IRQCHIP_SKIP_SET_WAKE	  |
>  				  IRQCHIP_MASK_ON_SUSPEND,
> @@ -1213,6 +1233,7 @@ static void gicv5_enable_nmi_support(void)
>  	gicv5_ppi_irq_chip.flags |= IRQCHIP_SUPPORTS_NMI;
>  	gicv5_spi_irq_chip.flags |= IRQCHIP_SUPPORTS_NMI;
>  	gicv5_lpi_irq_chip.flags |= IRQCHIP_SUPPORTS_NMI;
> +	gicv5_ipi_irq_chip.flags |= IRQCHIP_SUPPORTS_NMI;
>  }
>  
>  static void __init gicv5_smp_init(void)
> diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
> index b7d52821837b..114fd63b0210 100644
> --- a/kernel/irq/handle.c
> +++ b/kernel/irq/handle.c
> @@ -245,7 +245,8 @@ irqreturn_t handle_irq_event_percpu(struct irq_desc *desc)
>  
>  	retval = __handle_irq_event_percpu(desc);
>  
> -	add_interrupt_randomness(desc->irq_data.irq);
> +	if (!in_nmi())
> +		add_interrupt_randomness(desc->irq_data.irq);

This also needs to be a separate patch.

>  
>  	if (!irq_settings_no_debug(desc))
>  		note_interrupt(desc, retval);
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 7eb07e3bdb4c..0091bb5f7662 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -1370,9 +1370,14 @@ static bool irq_supports_nmi(struct irq_desc *desc)
>  	struct irq_data *d = irq_desc_get_irq_data(desc);
>  
>  #ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
> -	/* Only IRQs directly managed by the root irqchip can be set as NMI */
> -	if (d->parent_data)
> -		return false;
> +	struct irq_data *data;
> +	/*
> +	 * Only IRQs directly managed by the root irqchip can be set
> +	 * as NMI unless we inherit NMI from parent
> +	 */
> +	for (data = d->parent_data; data; data = data->parent_data)
> +		if (!(data->chip && data->chip->flags & IRQCHIP_SUPPORTS_NMI))
> +			return false;

Maybe we should just trust the local irqchip to do the right
thing. After all, the core code shouldn't be in the business of
sanitising broken irqchip drivers advertising random crap.

>  #endif
>  	/* Don't support NMIs for chips behind a slow bus */
>  	if (d->chip->irq_bus_lock || d->chip->irq_bus_sync_unlock)

Thanks,

	M.

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