Merge tag 'crc-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux

Pull CRC updates from Eric Biggers:
 "Update crc_kunit to test the CRC functions in softirq and hardirq
  contexts, similar to what the lib/crypto/ KUnit tests do. Move the
  helper function needed to do this into a common header.

  This is useful mainly to test fallback code paths for when
  FPU/SIMD/vector registers are unusable"

* tag 'crc-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux:
  Documentation/staging: Fix typo and incorrect citation in crc32.rst
  lib/crc: Drop inline from all *_mod_init_arch() functions
  lib/crc: Use underlying functions instead of crypto_simd_usable()
  lib/crc: crc_kunit: Test CRC computation in interrupt contexts
  kunit, lib/crypto: Move run_irq_test() to common header

1 files changed, 129 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..108e96433ea4
--- /dev/null
+++ b/include/kunit/run-in-irq-context.h
@@ -0,0 +1,129 @@
+/* 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>
+
+#define KUNIT_IRQ_TEST_HRTIMER_INTERVAL us_to_ktime(5)
+
+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;
+	unsigned long hardirq_func_calls;
+	unsigned long softirq_func_calls;
+	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);
+
+	WARN_ON_ONCE(!in_hardirq());
+	state->hardirq_func_calls++;
+
+	if (!state->func(state->test_specific_state))
+		state->hardirq_func_reported_failure = true;
+
+	hrtimer_forward_now(&state->timer, KUNIT_IRQ_TEST_HRTIMER_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());
+	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.
+ *
+ * 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,
+	};
+	unsigned long end_jiffies;
+
+	/*
+	 * 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 or 1 second, whichever comes first. */
+	end_jiffies = jiffies + HZ;
+	hrtimer_start(&state.timer, KUNIT_IRQ_TEST_HRTIMER_INTERVAL,
+		      HRTIMER_MODE_REL_HARD);
+	for (int i = 0; i < max_iterations && !time_after(jiffies, end_jiffies);
+	     i++) {
+		if (!func(test_specific_state))
+			state.task_func_reported_failure = true;
+	}
+
+	/* 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, state.hardirq_func_calls, 0,
+			    "Timer function was not called");
+	KUNIT_EXPECT_GT_MSG(test, state.softirq_func_calls, 0,
+			    "BH work function was not called");
+
+	/* Check for incorrect hash values reported from any context. */
+	KUNIT_EXPECT_FALSE_MSG(
+		test, state.task_func_reported_failure,
+		"Incorrect hash values reported from task context");
+	KUNIT_EXPECT_FALSE_MSG(
+		test, state.hardirq_func_reported_failure,
+		"Incorrect hash values reported from hardirq context");
+	KUNIT_EXPECT_FALSE_MSG(
+		test, state.softirq_func_reported_failure,
+		"Incorrect hash values reported from softirq context");
+}
+
+#endif /* _KUNIT_RUN_IN_IRQ_CONTEXT_H */