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Subject[tip: irq/core] genirq: Provide interrupt injection mechanism
The following commit has been merged into the irq/core branch of tip:

Commit-ID: acd26bcf362708594ea081ef55140e37d0854ed2
Gitweb: https://git.kernel.org/tip/acd26bcf362708594ea081ef55140e37d0854ed2
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Fri, 06 Mar 2020 14:03:47 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Sun, 08 Mar 2020 11:06:42 +01:00

genirq: Provide interrupt injection mechanism

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>
Tested-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lkml.kernel.org/r/20200306130623.990928309@linutronix.de

---
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(-)

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index c5fe60e..80f637c 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -248,6 +248,8 @@ extern void enable_percpu_nmi(unsigned int irq, unsigned int type);
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);
diff --git a/kernel/irq/Kconfig b/kernel/irq/Kconfig
index f92d9a6..20d501a 100644
--- 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---

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index b3fa2d8..41e7e37 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -278,7 +278,7 @@ int irq_startup(struct irq_desc *desc, bool resend, bool force)
}
}
if (resend)
- check_irq_resend(desc);
+ check_irq_resend(desc, false);

return ret;
}
diff --git a/kernel/irq/debugfs.c b/kernel/irq/debugfs.c
index 0c60779..4f9f844 100644
--- a/kernel/irq/debugfs.c
+++ b/kernel/irq/debugfs.c
@@ -190,39 +190,7 @@ static ssize_t irq_debug_write(struct file *file, const char __user *user_buf,
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;
}
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index 8980859..7db284b 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -108,7 +108,7 @@ irqreturn_t handle_irq_event_percpu(struct irq_desc *desc);
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);

diff --git a/kernel/irq/resend.c b/kernel/irq/resend.c
index bef72dc..27634f4 100644
--- a/kernel/irq/resend.c
+++ b/kernel/irq/resend.c
@@ -91,7 +91,7 @@ static int irq_sw_resend(struct irq_desc *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 *desc)
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 *desc)
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
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