@@ -2102,6 +2102,16 @@ config ARM64_MTE_COMP
 
 	  128-byte tag buffers corresponding to 4K pages can be compressed to save heap memory.
 
+config ARM64_MTE_COMP_KUNIT_TEST
+	tristate "Test tag compression for ARM64 Memory Tagging Extension" if !KUNIT_ALL_TESTS
+	default KUNIT_ALL_TESTS
+	depends on KUNIT && ARM64_MTE_COMP
+	help
+	  Test MTE compression algorithm enabled by CONFIG_ARM64_MTE_COMP.
+
+	  Ensure that tag sequences containing alternating values are compressed
+	  to buffers of expected size and correctly decompressed afterwards.
+
 config ARM64_SVE
 	bool "ARM Scalable Vector Extension support"
 	default y

@@ -11,6 +11,7 @@ obj-$(CONFIG_TRANS_TABLE)	+= trans_pgd-asm.o
 obj-$(CONFIG_DEBUG_VIRTUAL)	+= physaddr.o
 obj-$(CONFIG_ARM64_MTE)		+= mteswap.o
 obj-$(CONFIG_ARM64_MTE_COMP)	+= mtecomp.o
+obj-$(CONFIG_ARM64_MTE_COMP_KUNIT_TEST) += test_mtecomp.o
 KASAN_SANITIZE_physaddr.o	+= n
 
 obj-$(CONFIG_KASAN)		+= kasan_init.o

@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test cases for MTE tags compression algorithm.
+ */
+
+#include <linux/bits.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <kunit/test.h>
+#include <linux/types.h>
+
+#include <asm/mtecomp.h>
+
+/* Functions exported from mtecomp.c for this test. */
+void mte_tags_to_ranges(u8 *tags, u8 *out_tags, unsigned short *out_sizes,
+			size_t *out_len);
+void mte_ranges_to_tags(u8 *r_tags, unsigned short *r_sizes, size_t r_len,
+			u8 *tags);
+
+/*
+ * Test that mte_tags_to_ranges() produces a single range for a zero-filled tag
+ * buffer.
+ */
+static void test_tags_to_ranges_zero(struct kunit *test)
+{
+	u8 tags[128], dtags[128];
+	unsigned short r_sizes[256];
+	size_t r_len = 256;
+	u8 r_tags[256];
+
+	memset(tags, 0, 128);
+	mte_tags_to_ranges(tags, r_tags, r_sizes, &r_len);
+	KUNIT_EXPECT_EQ(test, r_len, 1);
+	KUNIT_EXPECT_EQ(test, r_tags[0], 0);
+	KUNIT_EXPECT_EQ(test, r_sizes[0], 256);
+	mte_ranges_to_tags(r_tags, r_sizes, r_len, dtags);
+	KUNIT_EXPECT_EQ(test, memcmp(tags, dtags, 128), 0);
+}
+
+/*
+ * Test that a small number of different tags is correctly transformed into
+ * ranges.
+ */
+static void test_tags_to_ranges_simple(struct kunit *test)
+{
+	u8 tags[128], dtags[128];
+	const u8 ex_tags[] = { 0xa, 0x0, 0xa, 0xb, 0x0 };
+	const unsigned short ex_sizes[] = { 1, 2, 2, 1, 250 };
+	unsigned short r_sizes[256];
+	size_t r_len = 256;
+	u8 r_tags[256];
+
+	memset(tags, 0, 128);
+	tags[0] = 0xa0;
+	tags[1] = 0x0a;
+	tags[2] = 0xab;
+	mte_tags_to_ranges(tags, r_tags, r_sizes, &r_len);
+	KUNIT_EXPECT_EQ(test, r_len, 5);
+	KUNIT_EXPECT_EQ(test, memcmp(r_tags, ex_tags, sizeof(ex_tags)), 0);
+	KUNIT_EXPECT_EQ(test, memcmp(r_sizes, ex_sizes, sizeof(ex_sizes)), 0);
+	mte_ranges_to_tags(r_tags, r_sizes, r_len, dtags);
+	KUNIT_EXPECT_EQ(test, memcmp(tags, dtags, 128), 0);
+}
+
+/* Test that repeated 0xa0 byte produces 256 ranges of length 1. */
+static void test_tags_to_ranges_repeated(struct kunit *test)
+{
+	u8 tags[128], dtags[128];
+	unsigned short r_sizes[256];
+	size_t r_len = 256;
+	u8 r_tags[256];
+
+	memset(tags, 0xa0, 128);
+	mte_tags_to_ranges(tags, r_tags, r_sizes, &r_len);
+	KUNIT_EXPECT_EQ(test, r_len, 256);
+	mte_ranges_to_tags(r_tags, r_sizes, r_len, dtags);
+	KUNIT_EXPECT_EQ(test, memcmp(tags, dtags, 128), 0);
+}
+
+/* Generate a buffer that will contain @nranges of tag ranges. */
+static void gen_tag_range_helper(u8 *tags, int nranges)
+{
+	unsigned int i;
+
+	memset(tags, 0, 128);
+	if (nranges > 1) {
+		nranges--;
+		for (i = 0; i < nranges / 2; i++)
+			tags[i] = 0xab;
+		if (nranges % 2)
+			tags[nranges / 2] = 0xa0;
+	}
+}
+
+/*
+ * Test that mte_tags_to_ranges()/mte_ranges_to_tags() work for various
+ * r_len values.
+ */
+static void test_tag_to_ranges_n(struct kunit *test)
+{
+	unsigned short r_sizes[256];
+	u8 tags[128], dtags[128];
+	unsigned int i, j, sum;
+	size_t r_len = 256;
+	u8 r_tags[256];
+
+	for (i = 1; i <= 256; i++) {
+		gen_tag_range_helper(tags, i);
+		mte_tags_to_ranges(tags, r_tags, r_sizes, &r_len);
+		sum = 0;
+		for (j = 0; j < r_len; j++)
+			sum += r_sizes[j];
+		KUNIT_EXPECT_EQ(test, sum, 256);
+		mte_ranges_to_tags(r_tags, r_sizes, r_len, dtags);
+		KUNIT_EXPECT_EQ(test, memcmp(tags, dtags, 128), 0);
+	}
+}
+
+/* Test that a zero-filled array is compressed into inline storage. */
+static void test_compress_zero(struct kunit *test)
+{
+	u8 tags[128], dtags[128];
+	unsigned long handle;
+
+	memset(tags, 0, 128);
+	handle = mte_compress(tags);
+	KUNIT_EXPECT_EQ(test, handle & BIT_ULL(63), 0);
+	/* Tags are stored inline. */
+	KUNIT_EXPECT_EQ(test, mte_storage_size(handle), 8);
+	KUNIT_EXPECT_TRUE(test, mte_decompress(handle, dtags));
+	KUNIT_EXPECT_EQ(test, memcmp(tags, dtags, 128), 0);
+}
+
+/*
+ * Test that a very small number of tag ranges ends up compressed into 8 bytes.
+ */
+static void test_compress_simple(struct kunit *test)
+{
+	u8 tags[128], dtags[128];
+	unsigned long handle;
+
+	memset(tags, 0, 128);
+	tags[0] = 0xa0;
+	tags[1] = 0x0a;
+	tags[2] = 0xab;
+
+	handle = mte_compress(tags);
+	KUNIT_EXPECT_EQ(test, handle & BIT_ULL(63), 0);
+	/* Tags are stored inline. */
+	KUNIT_EXPECT_EQ(test, mte_storage_size(handle), 8);
+	KUNIT_EXPECT_TRUE(test, mte_decompress(handle, dtags));
+	KUNIT_EXPECT_EQ(test, memcmp(tags, dtags, 128), 0);
+}
+
+/*
+ * Test that a buffer containing @nranges ranges compresses into @exp_size
+ * bytes and decompresses into the original tag sequence.
+ */
+static void compress_range_helper(struct kunit *test, int nranges,
+				  size_t exp_size)
+{
+	u8 tags[128], dtags[128];
+	unsigned long handle;
+
+	gen_tag_range_helper(tags, nranges);
+	handle = mte_compress(tags);
+	KUNIT_EXPECT_EQ(test, handle & BIT_ULL(63), 0);
+	KUNIT_EXPECT_EQ(test, mte_storage_size(handle), exp_size);
+	KUNIT_EXPECT_TRUE(test, mte_decompress(handle, dtags));
+	KUNIT_EXPECT_EQ(test, memcmp(tags, dtags, 128), 0);
+}
+
+/*
+ * Test that every number of tag ranges is correctly compressed and
+ * decompressed.
+ */
+static void test_compress_ranges(struct kunit *test)
+{
+	size_t exp_size;
+	unsigned int i;
+
+	for (i = 1; i <= 256; i++) {
+		if (i < 7)
+			exp_size = 8;
+		else if (i < 12)
+			exp_size = 16;
+		else if (i < 24)
+			exp_size = 32;
+		else if (i < 47)
+			exp_size = 64;
+		else
+			exp_size = 128;
+		compress_range_helper(test, i, exp_size);
+	}
+}
+
+static struct kunit_case mtecomp_test_cases[] = {
+	KUNIT_CASE(test_tags_to_ranges_zero),
+	KUNIT_CASE(test_tags_to_ranges_simple),
+	KUNIT_CASE(test_tags_to_ranges_repeated),
+	KUNIT_CASE(test_tag_to_ranges_n),
+	KUNIT_CASE(test_compress_zero),
+	KUNIT_CASE(test_compress_simple),
+	KUNIT_CASE(test_compress_ranges),
+	{}
+};
+
+static struct kunit_suite mtecomp_test_suite = {
+	.name = "mtecomp",
+	.test_cases = mtecomp_test_cases,
+};
+kunit_test_suites(&mtecomp_test_suite);
+
+MODULE_IMPORT_NS(MTECOMP);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Alexander Potapenko <glider@google.com>");