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    SubjectRe: [PATCH v5 2/4] genirq: Provide NMI management for percpu_devid interrupts
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    On 28/01/2019 16:41, Marc Zyngier wrote:
    > On Mon, 28 Jan 2019 15:38:25 +0000,
    > Julien Thierry <julien.thierry@arm.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@arm.com>
    >> Cc: Thomas Gleixner <tglx@linutronix.de>
    >> Cc: Peter Zijlstra <peterz@infradead.org>
    >> Cc: Ingo Molnar <mingo@kernel.org>
    >> Cc: Marc Zyngier <marc.zyngier@arm.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"?
    >

    The reason I did not go for "setup_percpu_nmi" is because I didn't want
    it to be assimilated to "setup_irq"/"__setup_irq" which sets up all the
    resources for an IRQ line.

    I guess "prepare_percpu_nmi()" could do the trick unless I come up with
    a better name.

    >> +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.
    >

    Sure, I can elaborate a bit.

    >> +{
    >> + 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.
    >

    Oh yes, well spotted!

    Thanks,

    >> + }
    >> +
    >> + 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.
    >

    --
    Julien Thierry

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