Message-ID: <86h8dsviny.wl-marc.zyngier@arm.com>
Date:   Mon, 28 Jan 2019 16:41:37 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Julien Thierry <julien.thierry@....com>
Cc:     <linux-kernel@...r.kernel.org>, <tglx@...utronix.de>,
        <peterz@...radead.org>, <mingo@...nel.org>
Subject: Re: [PATCH v5 2/4] genirq: Provide NMI management for percpu_devid interrupts

On Mon, 28 Jan 2019 15:38:25 +0000,
Julien Thierry <julien.thierry@....com> wrote:
> 
> Add support for percpu_devid interrupts treated as NMIs.
> 
> Percpu_devid NMIs need to be setup/torn down on each CPU they target.
> 
> The same restrictions as for global NMIs still apply for percpu_devid NMIs.

A quick overall view of the new API would be good, specially as some
of the bits are not 100% obvious.

> 
> Signed-off-by: Julien Thierry <julien.thierry@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Marc Zyngier <marc.zyngier@....com>
> ---
>  include/linux/interrupt.h |   9 +++
>  kernel/irq/manage.c       | 148 ++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 157 insertions(+)
> 
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index 37a4b0c6..be146bd 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -168,10 +168,15 @@ struct irqaction {
>  				    devname, percpu_dev_id);
>  }
>  
> +extern int __must_check
> +request_percpu_nmi(unsigned int irq, irq_handler_t handler,
> +		   const char *devname, void __percpu *dev);
> +
>  extern const void *free_irq(unsigned int, void *);
>  extern void free_percpu_irq(unsigned int, void __percpu *);
>  
>  extern const void *free_nmi(unsigned int irq, void *dev_id);
> +extern void free_percpu_nmi(unsigned int irq, void __percpu *percpu_dev_id);
>  
>  struct device;
>  
> @@ -224,7 +229,11 @@ struct irqaction {
>  extern void irq_wake_thread(unsigned int irq, void *dev_id);
>  
>  extern void disable_nmi_nosync(unsigned int irq);
> +extern void disable_percpu_nmi(unsigned int irq);
>  extern void enable_nmi(unsigned int irq);
> +extern void enable_percpu_nmi(unsigned int irq, unsigned int type);
> +extern int ready_percpu_nmi(unsigned int irq);

ready_percpu_nmi seems a very bizarre name, as I cannot figure out
what that does. How about something along the line of
"setup_percpu_nmi"?

> +extern void teardown_percpu_nmi(unsigned int irq);
>  
>  /* The following three functions are for the core kernel use only. */
>  extern void suspend_device_irqs(void);
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index a168b2d8f..602a622 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -2185,6 +2185,11 @@ void enable_percpu_irq(unsigned int irq, unsigned int type)
>  }
>  EXPORT_SYMBOL_GPL(enable_percpu_irq);
>  
> +void enable_percpu_nmi(unsigned int irq, unsigned int type)
> +{
> +	enable_percpu_irq(irq, type);
> +}
> +
>  /**
>   * irq_percpu_is_enabled - Check whether the per cpu irq is enabled
>   * @irq:	Linux irq number to check for
> @@ -2224,6 +2229,11 @@ void disable_percpu_irq(unsigned int irq)
>  }
>  EXPORT_SYMBOL_GPL(disable_percpu_irq);
>  
> +void disable_percpu_nmi(unsigned int irq)
> +{
> +	disable_percpu_irq(irq);
> +}
> +
>  /*
>   * Internal function to unregister a percpu irqaction.
>   */
> @@ -2255,6 +2265,8 @@ static struct irqaction *__free_percpu_irq(unsigned int irq, void __percpu *dev_
>  	/* Found it - now remove it from the list of entries: */
>  	desc->action = NULL;
>  
> +	desc->istate &= ~IRQS_NMI;
> +
>  	raw_spin_unlock_irqrestore(&desc->lock, flags);
>  
>  	unregister_handler_proc(irq, action);
> @@ -2308,6 +2320,19 @@ void free_percpu_irq(unsigned int irq, void __percpu *dev_id)
>  }
>  EXPORT_SYMBOL_GPL(free_percpu_irq);
>  
> +void free_percpu_nmi(unsigned int irq, void __percpu *dev_id)
> +{
> +	struct irq_desc *desc = irq_to_desc(irq);
> +
> +	if (!desc || !irq_settings_is_per_cpu_devid(desc))
> +		return;
> +
> +	if (WARN_ON(!(desc->istate & IRQS_NMI)))
> +		return;
> +
> +	kfree(__free_percpu_irq(irq, dev_id));
> +}
> +
>  /**
>   *	setup_percpu_irq - setup a per-cpu interrupt
>   *	@irq: Interrupt line to setup
> @@ -2398,6 +2423,129 @@ int __request_percpu_irq(unsigned int irq, irq_handler_t handler,
>  EXPORT_SYMBOL_GPL(__request_percpu_irq);
>  
>  /**
> + *	request_percpu_nmi - allocate a percpu interrupt line for NMI delivery
> + *	@irq: Interrupt line to allocate
> + *	@handler: Function to be called when the IRQ occurs.
> + *	@name: An ascii name for the claiming device
> + *	@dev_id: A percpu cookie passed back to the handler function
> + *
> + *	This call allocates interrupt resources for a per CPU NMI. Per CPU NMIs
> + *	have to be setup on each CPU by calling ready_percpu_nmi() before being
> + *	enabled on the same CPU by using enable_percpu_nmi().
> + *
> + *	Dev_id must be globally unique. It is a per-cpu variable, and
> + *	the handler gets called with the interrupted CPU's instance of
> + *	that variable.
> + *
> + *	Interrupt lines requested for NMI delivering should have auto enabling
> + *	setting disabled.
> + *
> + *	If the interrupt line cannot be used to deliver NMIs, function
> + *	will fail returning a negative value.
> + */
> +int request_percpu_nmi(unsigned int irq, irq_handler_t handler,
> +		       const char *name, void __percpu *dev_id)
> +{
> +	struct irqaction *action;
> +	struct irq_desc *desc;
> +	unsigned long flags;
> +	int retval;
> +
> +	if (!handler)
> +		return -EINVAL;
> +
> +	desc = irq_to_desc(irq);
> +
> +	if (!desc || !irq_settings_can_request(desc) ||
> +	    !irq_settings_is_per_cpu_devid(desc) ||
> +	    irq_settings_can_autoenable(desc) ||
> +	    !irq_supports_nmi(desc))
> +		return -EINVAL;
> +
> +	/* The line cannot already be NMI */
> +	if (desc->istate & IRQS_NMI)
> +		return -EINVAL;
> +
> +	action = kzalloc(sizeof(struct irqaction), GFP_KERNEL);
> +	if (!action)
> +		return -ENOMEM;
> +
> +	action->handler = handler;
> +	action->flags = IRQF_PERCPU | IRQF_NO_SUSPEND | IRQF_NO_THREAD
> +		| IRQF_NOBALANCING;
> +	action->name = name;
> +	action->percpu_dev_id = dev_id;
> +
> +	retval = irq_chip_pm_get(&desc->irq_data);
> +	if (retval < 0)
> +		goto err_out;
> +
> +	retval = __setup_irq(irq, desc, action);
> +	if (retval)
> +		goto err_irq_setup;
> +
> +	raw_spin_lock_irqsave(&desc->lock, flags);
> +	desc->istate |= IRQS_NMI;
> +	raw_spin_unlock_irqrestore(&desc->lock, flags);
> +
> +	return 0;
> +
> +err_irq_setup:
> +	irq_chip_pm_put(&desc->irq_data);
> +err_out:
> +	kfree(action);
> +
> +	return retval;
> +}
> +
> +int ready_percpu_nmi(unsigned int irq)

Name issue withstanding, this could do with some documentation. You
probably want to indicate that this is expected to be called from a
non-preemptible section.

> +{
> +	unsigned long flags;
> +	struct irq_desc *desc = irq_get_desc_lock(irq, &flags,
> +						  IRQ_GET_DESC_CHECK_PERCPU);
> +	int ret = 0;
> +
> +	if (!desc) {
> +		ret = -EINVAL;
> +		goto out;

Ouch. Bad idea.

> +	}
> +
> +	if (WARN(!(desc->istate & IRQS_NMI),
> +		 KERN_ERR "ready_percpu_nmi called for a non-NMI interrupt: irq %u\n",
> +		 irq)) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	ret = irq_nmi_setup(desc);
> +	if (ret) {
> +		pr_err("Failed to setup NMI delivery: irq %u\n", irq);
> +		goto out;
> +	}
> +
> +out:
> +	irq_put_desc_unlock(desc, flags);
> +	return ret;
> +}
> +
> +void teardown_percpu_nmi(unsigned int irq)
> +{
> +	unsigned long flags;
> +	struct irq_desc *desc = irq_get_desc_lock(irq, &flags,
> +						  IRQ_GET_DESC_CHECK_PERCPU);
> +
> +	if (!desc)
> +		return;
> +
> +	if (WARN_ON(!(desc->istate & IRQS_NMI)))
> +		goto out;
> +
> +	irq_nmi_teardown(desc);
> +out:
> +	irq_put_desc_unlock(desc, flags);
> +}
> +
> +/**
>   *	irq_get_irqchip_state - returns the irqchip state of a interrupt.
>   *	@irq: Interrupt line that is forwarded to a VM
>   *	@which: One of IRQCHIP_STATE_* the caller wants to know about
> -- 
> 1.9.1
> 

Thanks,

	M.

-- 
Jazz is not dead, it just smell funny.

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