xor: add a kunit test case

Add a test case for the XOR routines loosely based on the CRC kunit
test.

Link: https://lkml.kernel.org/r/20260327061704.3707577-29-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Eric Biggers <ebiggers@kernel.org>
Tested-by: Eric Biggers <ebiggers@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chris Mason <clm@fb.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Sterba <dsterba@suse.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jason A. Donenfeld <jason@zx2c4.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Li Nan <linan122@huawei.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Magnus Lindholm <linmag7@gmail.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Song Liu <song@kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Ted Ts'o <tytso@mit.edu>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/raid/.kunitconfig

@@ -0,0 +1,3 @@
+CONFIG_KUNIT=y
+CONFIG_BTRFS_FS=y
+CONFIG_XOR_KUNIT_TEST=y

lib/raid/Kconfig

@@ -17,3 +17,14 @@ config XOR_BLOCKS_ARCH
 	default y if X86_32
 	default y if X86_64
 	bool
+
+config XOR_KUNIT_TEST
+	tristate "KUnit tests for xor_gen" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	depends on XOR_BLOCKS
+	default KUNIT_ALL_TESTS
+	help
+	  Unit tests for the XOR library functions.
+
+	  This is intended to help people writing architecture-specific
+	  optimized versions.  If unsure, say N.

lib/raid/xor/Makefile

@@ -29,7 +29,7 @@ xor-$(CONFIG_SPARC64)		+= sparc/xor-sparc64.o sparc/xor-sparc64-glue.o
 xor-$(CONFIG_S390)		+= s390/xor.o
 xor-$(CONFIG_X86_32)		+= x86/xor-avx.o x86/xor-sse.o x86/xor-mmx.o
 xor-$(CONFIG_X86_64)		+= x86/xor-avx.o x86/xor-sse.o
-
+obj-y				+= tests/
 
 CFLAGS_arm/xor-neon.o		+= $(CC_FLAGS_FPU)
 CFLAGS_REMOVE_arm/xor-neon.o	+= $(CC_FLAGS_NO_FPU)

lib/raid/xor/tests/Makefile

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+obj-$(CONFIG_XOR_KUNIT_TEST) += xor_kunit.o

lib/raid/xor/tests/xor_kunit.c

@@ -0,0 +1,187 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Unit test the XOR library functions.
+ *
+ * Copyright 2024 Google LLC
+ * Copyright 2026 Christoph Hellwig
+ *
+ * Based on the CRC tests by Eric Biggers <ebiggers@google.com>.
+ */
+#include <kunit/test.h>
+#include <linux/prandom.h>
+#include <linux/string_choices.h>
+#include <linux/vmalloc.h>
+#include <linux/raid/xor.h>
+
+#define XOR_KUNIT_SEED			42
+#define XOR_KUNIT_MAX_BYTES		16384
+#define XOR_KUNIT_MAX_BUFFERS		64
+#define XOR_KUNIT_NUM_TEST_ITERS	1000
+
+static struct rnd_state rng;
+static void *test_buffers[XOR_KUNIT_MAX_BUFFERS];
+static void *test_dest;
+static void *test_ref;
+static size_t test_buflen;
+
+static u32 rand32(void)
+{
+	return prandom_u32_state(&rng);
+}
+
+/* Reference implementation using dumb byte-wise XOR */
+static void xor_ref(void *dest, void **srcs, unsigned int src_cnt,
+		unsigned int bytes)
+{
+	unsigned int off, idx;
+	u8 *d = dest;
+
+	for (off = 0; off < bytes; off++) {
+		for (idx = 0; idx < src_cnt; idx++) {
+			u8 *src = srcs[idx];
+
+			d[off] ^= src[off];
+		}
+	}
+}
+
+/* Generate a random length that is a multiple of 512. */
+static unsigned int random_length(unsigned int max_length)
+{
+	return round_up((rand32() % max_length) + 1, 512);
+}
+
+/* Generate a random alignment that is a multiple of 64. */
+static unsigned int random_alignment(unsigned int max_alignment)
+{
+	return ((rand32() % max_alignment) + 1) & ~63;
+}
+
+static void xor_generate_random_data(void)
+{
+	int i;
+
+	prandom_bytes_state(&rng, test_dest, test_buflen);
+	memcpy(test_ref, test_dest, test_buflen);
+	for (i = 0; i < XOR_KUNIT_MAX_BUFFERS; i++)
+		prandom_bytes_state(&rng, test_buffers[i], test_buflen);
+}
+
+/* Test that xor_gen gives the same result as a reference implementation. */
+static void xor_test(struct kunit *test)
+{
+	void *aligned_buffers[XOR_KUNIT_MAX_BUFFERS];
+	size_t i;
+
+	for (i = 0; i < XOR_KUNIT_NUM_TEST_ITERS; i++) {
+		unsigned int nr_buffers =
+			(rand32() % XOR_KUNIT_MAX_BUFFERS) + 1;
+		unsigned int len = random_length(XOR_KUNIT_MAX_BYTES);
+		unsigned int max_alignment, align = 0;
+		void *buffers;
+
+		if (rand32() % 8 == 0)
+			/* Refresh the data occasionally. */
+			xor_generate_random_data();
+
+		/*
+		 * If we're not using the entire buffer size, inject randomize
+		 * alignment into the buffer.
+		 */
+		max_alignment = XOR_KUNIT_MAX_BYTES - len;
+		if (max_alignment == 0) {
+			buffers = test_buffers;
+		} else if (rand32() % 2 == 0) {
+			/* Use random alignments mod 64 */
+			int j;
+
+			for (j = 0; j < nr_buffers; j++)
+				aligned_buffers[j] = test_buffers[j] +
+					random_alignment(max_alignment);
+			buffers = aligned_buffers;
+			align = random_alignment(max_alignment);
+		} else {
+			/* Go up to the guard page, to catch buffer overreads */
+			int j;
+
+			align = test_buflen - len;
+			for (j = 0; j < nr_buffers; j++)
+				aligned_buffers[j] = test_buffers[j] + align;
+			buffers = aligned_buffers;
+		}
+
+		/*
+		 * Compute the XOR, and verify that it equals the XOR computed
+		 * by a simple byte-at-a-time reference implementation.
+		 */
+		xor_ref(test_ref + align, buffers, nr_buffers, len);
+		xor_gen(test_dest + align, buffers, nr_buffers, len);
+		KUNIT_EXPECT_MEMEQ_MSG(test, test_ref + align,
+				test_dest + align, len,
+				"Wrong result with buffers=%u, len=%u, unaligned=%s, at_end=%s",
+				nr_buffers, len,
+				str_yes_no(max_alignment),
+				str_yes_no(align + len == test_buflen));
+	}
+}
+
+static struct kunit_case xor_test_cases[] = {
+	KUNIT_CASE(xor_test),
+	{},
+};
+
+static int xor_suite_init(struct kunit_suite *suite)
+{
+	int i;
+
+	/*
+	 * Allocate the test buffer using vmalloc() with a page-aligned length
+	 * so that it is immediately followed by a guard page.  This allows
+	 * buffer overreads to be detected, even in assembly code.
+	 */
+	test_buflen = round_up(XOR_KUNIT_MAX_BYTES, PAGE_SIZE);
+	test_ref = vmalloc(test_buflen);
+	if (!test_ref)
+		return -ENOMEM;
+	test_dest = vmalloc(test_buflen);
+	if (!test_dest)
+		goto out_free_ref;
+	for (i = 0; i < XOR_KUNIT_MAX_BUFFERS; i++) {
+		test_buffers[i] = vmalloc(test_buflen);
+		if (!test_buffers[i])
+			goto out_free_buffers;
+	}
+
+	prandom_seed_state(&rng, XOR_KUNIT_SEED);
+	xor_generate_random_data();
+	return 0;
+
+out_free_buffers:
+	while (--i >= 0)
+		vfree(test_buffers[i]);
+	vfree(test_dest);
+out_free_ref:
+	vfree(test_ref);
+	return -ENOMEM;
+}
+
+static void xor_suite_exit(struct kunit_suite *suite)
+{
+	int i;
+
+	vfree(test_ref);
+	vfree(test_dest);
+	for (i = 0; i < XOR_KUNIT_MAX_BUFFERS; i++)
+		vfree(test_buffers[i]);
+}
+
+static struct kunit_suite xor_test_suite = {
+	.name		= "xor",
+	.test_cases	= xor_test_cases,
+	.suite_init	= xor_suite_init,
+	.suite_exit	= xor_suite_exit,
+};
+kunit_test_suite(xor_test_suite);
+
+MODULE_DESCRIPTION("Unit test for the XOR library functions");
+MODULE_LICENSE("GPL");