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SubjectRe: [patch 6/7] genirq: Provide interrupt injection mechanism
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Date
Hi,

On 3/6/20 5:03 AM, Thomas Gleixner wrote:
> Error injection mechanisms need a half ways safe way to inject interrupts as
> invoking generic_handle_irq() or the actual device interrupt handler
> directly from e.g. a debugfs write is not guaranteed to be safe.
>
> On x86 generic_handle_irq() is unsafe due to the hardware trainwreck which
> is the base of x86 interrupt delivery and affinity management.
>
> Move the irq debugfs injection code into a separate function which can be
> used by error injection code as well.
>
> The implementation prevents at least that state is corrupted, but it cannot
> close a very tiny race window on x86 which might result in a stale and not
> serviced device interrupt under very unlikely circumstances.
>
> This is explicitly for debugging and testing and not for production use or
> abuse in random driver code.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com>
Tested-by: Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com>
> ---
> include/linux/interrupt.h | 2 +
> kernel/irq/Kconfig | 5 ++++
> kernel/irq/chip.c | 2 -
> kernel/irq/debugfs.c | 34 -----------------------------
> kernel/irq/internals.h | 2 -
> kernel/irq/resend.c | 53 ++++++++++++++++++++++++++++++++++++++++++++--
> 6 files changed, 61 insertions(+), 37 deletions(-)
>
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -248,6 +248,8 @@ extern void enable_percpu_nmi(unsigned i
> extern int prepare_percpu_nmi(unsigned int irq);
> extern void teardown_percpu_nmi(unsigned int irq);
>
> +extern int irq_inject_interrupt(unsigned int irq);
> +
> /* The following three functions are for the core kernel use only. */
> extern void suspend_device_irqs(void);
> extern void resume_device_irqs(void);
> --- a/kernel/irq/Kconfig
> +++ b/kernel/irq/Kconfig
> @@ -43,6 +43,10 @@ config GENERIC_IRQ_MIGRATION
> config AUTO_IRQ_AFFINITY
> bool
>
> +# Interrupt injection mechanism
> +config GENERIC_IRQ_INJECTION
> + bool
> +
> # Tasklet based software resend for pending interrupts on enable_irq()
> config HARDIRQS_SW_RESEND
> bool
> @@ -127,6 +131,7 @@ config SPARSE_IRQ
> config GENERIC_IRQ_DEBUGFS
> bool "Expose irq internals in debugfs"
> depends on DEBUG_FS
> + select GENERIC_IRQ_INJECTION
> default n
> ---help---
>
> --- a/kernel/irq/chip.c
> +++ b/kernel/irq/chip.c
> @@ -278,7 +278,7 @@ int irq_startup(struct irq_desc *desc, b
> }
> }
> if (resend)
> - check_irq_resend(desc);
> + check_irq_resend(desc, false);
>
> return ret;
> }
> --- a/kernel/irq/debugfs.c
> +++ b/kernel/irq/debugfs.c
> @@ -190,39 +190,7 @@ static ssize_t irq_debug_write(struct fi
> return -EFAULT;
>
> if (!strncmp(buf, "trigger", size)) {
> - unsigned long flags;
> - int err;
> -
> - /* Try the HW interface first */
> - err = irq_set_irqchip_state(irq_desc_get_irq(desc),
> - IRQCHIP_STATE_PENDING, true);
> - if (!err)
> - return count;
> -
> - /*
> - * Otherwise, try to inject via the resend interface,
> - * which may or may not succeed.
> - */
> - chip_bus_lock(desc);
> - raw_spin_lock_irqsave(&desc->lock, flags);
> -
> - /*
> - * Don't allow injection when the interrupt is:
> - * - Level or NMI type
> - * - not activated
> - * - replaying already
> - */
> - if (irq_settings_is_level(desc) ||
> - !irqd_is_activated(&desc->irq_data) ||
> - (desc->istate & (IRQS_NMI | IRQS_REPLAY)) {
> - err = -EINVAL;
> - } else {
> - desc->istate |= IRQS_PENDING;
> - err = check_irq_resend(desc);
> - }
> -
> - raw_spin_unlock_irqrestore(&desc->lock, flags);
> - chip_bus_sync_unlock(desc);
> + int err = irq_inject_interrupt(irq_desc_get_irq(desc));
>
> return err ? err : count;
> }
> --- a/kernel/irq/internals.h
> +++ b/kernel/irq/internals.h
> @@ -108,7 +108,7 @@ irqreturn_t handle_irq_event_percpu(stru
> irqreturn_t handle_irq_event(struct irq_desc *desc);
>
> /* Resending of interrupts :*/
> -int check_irq_resend(struct irq_desc *desc);
> +int check_irq_resend(struct irq_desc *desc, bool inject);
> bool irq_wait_for_poll(struct irq_desc *desc);
> void __irq_wake_thread(struct irq_desc *desc, struct irqaction *action);
>
> --- a/kernel/irq/resend.c
> +++ b/kernel/irq/resend.c
> @@ -91,7 +91,7 @@ static int irq_sw_resend(struct irq_desc
> *
> * Is called with interrupts disabled and desc->lock held.
> */
> -int check_irq_resend(struct irq_desc *desc)
> +int check_irq_resend(struct irq_desc *desc, bool inject)
> {
> int err = 0;
>
> @@ -108,7 +108,7 @@ int check_irq_resend(struct irq_desc *de
> if (desc->istate & IRQS_REPLAY)
> return -EBUSY;
>
> - if (!(desc->istate & IRQS_PENDING))
> + if (!(desc->istate & IRQS_PENDING) && !inject)
> return 0;
>
> desc->istate &= ~IRQS_PENDING;
> @@ -122,3 +122,52 @@ int check_irq_resend(struct irq_desc *de
> desc->istate |= IRQS_REPLAY;
> return err;
> }
> +
> +#ifdef CONFIG_GENERIC_IRQ_INJECTION
> +/**
> + * irq_inject_interrupt - Inject an interrupt for testing/error injection
> + * @irq: The interrupt number
> + *
> + * This function must only be used for debug and testing purposes!
> + *
> + * Especially on x86 this can cause a premature completion of an interrupt
> + * affinity change causing the interrupt line to become stale. Very
> + * unlikely, but possible.
> + *
> + * The injection can fail for various reasons:
> + * - Interrupt is not activated
> + * - Interrupt is NMI type or currently replaying
> + * - Interrupt is level type
> + * - Interrupt does not support hardware retrigger and software resend is
> + * either not enabled or not possible for the interrupt.
> + */
> +int irq_inject_interrupt(unsigned int irq)
> +{
> + struct irq_desc *desc;
> + unsigned long flags;
> + int err;
> +
> + /* Try the state injection hardware interface first */
> + if (!irq_set_irqchip_state(irq, IRQCHIP_STATE_PENDING, true))
> + return 0;
> +
> + /* That failed, try via the resend mechanism */
> + desc = irq_get_desc_buslock(irq, &flags, 0);
> + if (!desc)
> + return -EINVAL;
> +
> + /*
> + * Only try to inject when the interrupt is:
> + * - not NMI type
> + * - activated
> + */
> + if ((desc->istate & IRQS_NMI) || !irqd_is_activated(&desc->irq_data))
> + err = -EINVAL;
> + else
> + err = check_irq_resend(desc, true);
> +
> + irq_put_desc_busunlock(desc, flags);
> + return err;
> +}
> +EXPORT_SYMBOL_GPL(irq_inject_interrupt);
> +#endif
>
--
Sathyanarayanan Kuppuswamy
Linux kernel developer

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