1 files changed, 154 insertions, 0 deletions
diff --git a/include/kunit/run-in-irq-context.h b/include/kunit/run-in-irq-context.h
new file mode 100644
index 000000000000..bfe60d6cf28d
--- /dev/null
+++ b/include/kunit/run-in-irq-context.h
@@ -0,0 +1,154 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Helper function for testing code in interrupt contexts
+ *
+ * Copyright 2025 Google LLC
+ */
+#ifndef _KUNIT_RUN_IN_IRQ_CONTEXT_H
+#define _KUNIT_RUN_IN_IRQ_CONTEXT_H
+
+#include <kunit/test.h>
+#include <linux/timekeeping.h>
+#include <linux/hrtimer.h>
+#include <linux/workqueue.h>
+
+struct kunit_irq_test_state {
+	bool (*func)(void *test_specific_state);
+	void *test_specific_state;
+	bool task_func_reported_failure;
+	bool hardirq_func_reported_failure;
+	bool softirq_func_reported_failure;
+	atomic_t task_func_calls;
+	atomic_t hardirq_func_calls;
+	atomic_t softirq_func_calls;
+	ktime_t interval;
+	struct hrtimer timer;
+	struct work_struct bh_work;
+};
+
+static enum hrtimer_restart kunit_irq_test_timer_func(struct hrtimer *timer)
+{
+	struct kunit_irq_test_state *state =
+		container_of(timer, typeof(*state), timer);
+	int task_calls, hardirq_calls, softirq_calls;
+
+	WARN_ON_ONCE(!in_hardirq());
+	task_calls = atomic_read(&state->task_func_calls);
+	hardirq_calls = atomic_inc_return(&state->hardirq_func_calls);
+	softirq_calls = atomic_read(&state->softirq_func_calls);
+
+	/*
+	 * If the timer is firing too often for the softirq or task to ever have
+	 * a chance to run, increase the timer interval.  This is needed on very
+	 * slow systems.
+	 */
+	if (hardirq_calls >= 20 && (softirq_calls == 0 || task_calls == 0))
+		state->interval = ktime_add_ns(state->interval, 250);
+
+	if (!state->func(state->test_specific_state))
+		state->hardirq_func_reported_failure = true;
+
+	hrtimer_forward_now(&state->timer, state->interval);
+	queue_work(system_bh_wq, &state->bh_work);
+	return HRTIMER_RESTART;
+}
+
+static void kunit_irq_test_bh_work_func(struct work_struct *work)
+{
+	struct kunit_irq_test_state *state =
+		container_of(work, typeof(*state), bh_work);
+
+	WARN_ON_ONCE(!in_serving_softirq());
+	atomic_inc(&state->softirq_func_calls);
+
+	if (!state->func(state->test_specific_state))
+		state->softirq_func_reported_failure = true;
+}
+
+/*
+ * Helper function which repeatedly runs the given @func in task, softirq, and
+ * hardirq context concurrently, and reports a failure to KUnit if any
+ * invocation of @func in any context returns false.  @func is passed
+ * @test_specific_state as its argument.  At most 3 invocations of @func will
+ * run concurrently: one in each of task, softirq, and hardirq context.  @func
+ * will continue running until either @max_iterations calls have been made (so
+ * long as at least one each runs in task, softirq, and hardirq contexts), or
+ * one second has passed.
+ *
+ * The main purpose of this interrupt context testing is to validate fallback
+ * code paths that run in contexts where the normal code path cannot be used,
+ * typically due to the FPU or vector registers already being in-use in kernel
+ * mode.  These code paths aren't covered when the test code is executed only by
+ * the KUnit test runner thread in task context.  The reason for the concurrency
+ * is because merely using hardirq context is not sufficient to reach a fallback
+ * code path on some architectures; the hardirq actually has to occur while the
+ * FPU or vector unit was already in-use in kernel mode.
+ *
+ * Another purpose of this testing is to detect issues with the architecture's
+ * irq_fpu_usable() and kernel_fpu_begin/end() or equivalent functions,
+ * especially in softirq context when the softirq may have interrupted a task
+ * already using kernel-mode FPU or vector (if the arch didn't prevent that).
+ * Crypto functions are often executed in softirqs, so this is important.
+ */
+static inline void kunit_run_irq_test(struct kunit *test, bool (*func)(void *),
+				      int max_iterations,
+				      void *test_specific_state)
+{
+	struct kunit_irq_test_state state = {
+		.func = func,
+		.test_specific_state = test_specific_state,
+		/*
+		 * Start with a 5us timer interval.  If the system can't keep
+		 * up, kunit_irq_test_timer_func() will increase it.
+		 */
+		.interval = us_to_ktime(5),
+	};
+	unsigned long end_jiffies;
+	int task_calls, hardirq_calls, softirq_calls;
+
+	/*
+	 * Set up a hrtimer (the way we access hardirq context) and a work
+	 * struct for the BH workqueue (the way we access softirq context).
+	 */
+	hrtimer_setup_on_stack(&state.timer, kunit_irq_test_timer_func,
+			       CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
+	INIT_WORK_ONSTACK(&state.bh_work, kunit_irq_test_bh_work_func);
+
+	/*
+	 * Run for up to max_iterations (including at least one task, softirq,
+	 * and hardirq), or 1 second, whichever comes first.
+	 */
+	end_jiffies = jiffies + HZ;
+	hrtimer_start(&state.timer, state.interval, HRTIMER_MODE_REL_HARD);
+	do {
+		if (!func(test_specific_state))
+			state.task_func_reported_failure = true;
+
+		task_calls = atomic_inc_return(&state.task_func_calls);
+		hardirq_calls = atomic_read(&state.hardirq_func_calls);
+		softirq_calls = atomic_read(&state.softirq_func_calls);
+	} while ((task_calls + hardirq_calls + softirq_calls < max_iterations ||
+		  (task_calls == 0 || hardirq_calls == 0 ||
+		   softirq_calls == 0)) &&
+		 !time_after(jiffies, end_jiffies));
+
+	/* Cancel the timer and work. */
+	hrtimer_cancel(&state.timer);
+	flush_work(&state.bh_work);
+
+	/* Sanity check: the timer and BH functions should have been run. */
+	KUNIT_EXPECT_GT_MSG(test, atomic_read(&state.hardirq_func_calls), 0,
+			    "Timer function was not called");
+	KUNIT_EXPECT_GT_MSG(test, atomic_read(&state.softirq_func_calls), 0,
+			    "BH work function was not called");
+
+	/* Check for failure reported from any context. */
+	KUNIT_EXPECT_FALSE_MSG(test, state.task_func_reported_failure,
+			       "Failure reported from task context");
+	KUNIT_EXPECT_FALSE_MSG(test, state.hardirq_func_reported_failure,
+			       "Failure reported from hardirq context");
+	KUNIT_EXPECT_FALSE_MSG(test, state.softirq_func_reported_failure,
+			       "Failure reported from softirq context");
+}
+
+#endif /* _KUNIT_RUN_IN_IRQ_CONTEXT_H */