[PATCH v7 4/5] arm64: mte: add a test for MTE tags compression

Alexander Potapenko
2023-10-11T17:29:06Z

Ensure that tag sequences containing alternating values are compressed
to buffers of expected size and correctly decompressed afterwards.

Signed-off-by: Alexander Potapenko <glider@google.com>

---
v6:
- add test_decompress_invalid() to ensure invalid handles are ignored;
- add test_upper_bits(), which is a regression test for a case where
an inline handle looked like an out-of-line one;
- add test_compress_nonzero() to ensure a full nonzero tag array is
compressed correctly;
- add test_two_ranges() to test cases when the input buffer is divided
into two ranges.

v5:
- remove hardcoded constants, added test setup/teardown;
- support 16- and 64K pages;
- replace nested if-clauses with expected_size_from_ranges();
- call mte_release_handle() after tests that perform
compression/decompression;
- address comments by Andy Shevchenko:
- fix include order;
- use mtecomp.h instead of function prototypes.

v4:
- addressed comments by Andy Shevchenko:
- expanded MTE to "Memory Tagging Extension" in Kconfig
- changed signed variables to unsigned where applicable
- added missing header dependencies

- addressed comments by Yury Norov:
- moved test-only declarations from mtecomp.h into this test
- switched to the new "mte"-prefixed function names, dropped the
mentions of "EA0"
- added test_tag_to_ranges_n()

v3:
- addressed comments by Andy Shevchenko in another patch:
- switched from u64 to unsigned long
- added MODULE_IMPORT_NS(MTECOMP)
- fixed includes order
---
arch/arm64/Kconfig | 10 +
arch/arm64/mm/Makefile | 1 +
arch/arm64/mm/test_mtecomp.c | 377 +++++++++++++++++++++++++++++++++++
3 files changed, 388 insertions(+)
create mode 100644 arch/arm64/mm/test_mtecomp.c

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index d4fb3b8d11d77..ffe3bec89df82 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -2104,6 +2104,16 @@ config ARM64_MTE_COMP
RLE to conserve heap memory. In the common case compressed tags
occupy 2.5x less 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
diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile
index 46778f6dd83c2..170dc62b010b9 100644
--- a/arch/arm64/mm/Makefile
+++ b/arch/arm64/mm/Makefile
@@ -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
diff --git a/arch/arm64/mm/test_mtecomp.c b/arch/arm64/mm/test_mtecomp.c
new file mode 100644
index 0000000000000..8fe50a214b38c
--- /dev/null
+++ b/arch/arm64/mm/test_mtecomp.c
@@ -0,0 +1,377 @@
+// 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 <linux/types.h>
+
+#include <kunit/test.h>
+
+#include <asm/mtecomp.h>
+
+#include "mtecomp.h"
+
+/* Per-test storage allocated in mtecomp_test_init(). */
+struct test_data {
+ u8 *tags, *dtags;
+ unsigned short *r_sizes;
+ size_t r_len;
+ u8 *r_tags;
+};
+
+/*
+ * Split td->tags to ranges stored in td->r_tags, td->r_sizes, td->r_len,
+ * then convert those ranges back to tags stored in td->dtags.
+ */
+static void tags_to_ranges_to_tags_helper(struct kunit *test)
+{
+ struct test_data *td = test->priv;
+
+ mte_tags_to_ranges(td->tags, td->r_tags, td->r_sizes, &td->r_len);
+ mte_ranges_to_tags(td->r_tags, td->r_sizes, td->r_len, td->dtags);
+ KUNIT_EXPECT_EQ(test, memcmp(td->tags, td->dtags, MTE_PAGE_TAG_STORAGE),
+ 0);
+}
+
+/*
+ * 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)
+{
+ struct test_data *td = test->priv;
+
+ memset(td->tags, 0, MTE_PAGE_TAG_STORAGE);
+ tags_to_ranges_to_tags_helper(test);
+
+ KUNIT_EXPECT_EQ(test, td->r_len, 1);
+ KUNIT_EXPECT_EQ(test, td->r_tags[0], 0);
+ KUNIT_EXPECT_EQ(test, td->r_sizes[0], MTE_GRANULES_PER_PAGE);
+}
+
+/*
+ * Test that a small number of different tags is correctly transformed into
+ * ranges.
+ */
+static void test_tags_to_ranges_simple(struct kunit *test)
+{
+ struct test_data *td = test->priv;
+ const u8 ex_tags[] = { 0xa, 0x0, 0xa, 0xb, 0x0 };
+ const unsigned short ex_sizes[] = { 1, 2, 2, 1,
+ MTE_GRANULES_PER_PAGE - 6 };
+
+ memset(td->tags, 0, MTE_PAGE_TAG_STORAGE);
+ td->tags[0] = 0xa0;
+ td->tags[1] = 0x0a;
+ td->tags[2] = 0xab;
+ tags_to_ranges_to_tags_helper(test);
+
+ KUNIT_EXPECT_EQ(test, td->r_len, 5);
+ KUNIT_EXPECT_EQ(test, memcmp(td->r_tags, ex_tags, sizeof(ex_tags)), 0);
+ KUNIT_EXPECT_EQ(test, memcmp(td->r_sizes, ex_sizes, sizeof(ex_sizes)),
+ 0);
+}
+
+/* Test that repeated 0xa0 byte produces MTE_GRANULES_PER_PAGE ranges of length 1. */
+static void test_tags_to_ranges_repeated(struct kunit *test)
+{
+ struct test_data *td = test->priv;
+
+ memset(td->tags, 0xa0, MTE_PAGE_TAG_STORAGE);
+ tags_to_ranges_to_tags_helper(test);
+
+ KUNIT_EXPECT_EQ(test, td->r_len, MTE_GRANULES_PER_PAGE);
+}
+
+/* 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, MTE_PAGE_TAG_STORAGE);
+ 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)
+{
+ struct test_data *td = test->priv;
+ unsigned int i, j, sum;
+
+ for (i = 1; i <= MTE_GRANULES_PER_PAGE; i++) {
+ gen_tag_range_helper(td->tags, i);
+ tags_to_ranges_to_tags_helper(test);
+ sum = 0;
+ for (j = 0; j < td->r_len; j++)
+ sum += td->r_sizes[j];
+ KUNIT_EXPECT_EQ(test, sum, MTE_GRANULES_PER_PAGE);
+ }
+}
+
+/*
+ * Check that the tag buffer in test->priv can be compressed and decompressed
+ * without changes.
+ */
+static unsigned long compress_decompress_helper(struct kunit *test)
+{
+ struct test_data *td = test->priv;
+ unsigned long handle;
+
+ handle = mte_compress(td->tags);
+ KUNIT_EXPECT_EQ(test, handle & BIT_ULL(63), 0);
+ KUNIT_EXPECT_TRUE(test, mte_decompress(handle, td->dtags));
+ KUNIT_EXPECT_EQ(test, memcmp(td->tags, td->dtags, MTE_PAGE_TAG_STORAGE),
+ 0);
+ return handle;
+}
+
+/* Test that a zero-filled array is compressed into inline storage. */
+static void test_compress_zero(struct kunit *test)
+{
+ struct test_data *td = test->priv;
+ unsigned long handle;
+
+ memset(td->tags, 0, MTE_PAGE_TAG_STORAGE);
+ handle = compress_decompress_helper(test);
+ /* Tags are stored inline. */
+ KUNIT_EXPECT_EQ(test, mte_storage_size(handle), 8);
+ mte_release_handle(handle);
+}
+
+/* Test that a 0xaa-filled array is compressed into inline storage. */
+static void test_compress_nonzero(struct kunit *test)
+{
+ struct test_data *td = test->priv;
+ unsigned long handle;
+
+ memset(td->tags, 0xaa, MTE_PAGE_TAG_STORAGE);
+ handle = compress_decompress_helper(test);
+ /* Tags are stored inline. */
+ KUNIT_EXPECT_EQ(test, mte_storage_size(handle), 8);
+ mte_release_handle(handle);
+}
+
+/*
+ * Test that two tag ranges are compressed into inline storage.
+ *
+ * This also covers a special case where both ranges contain
+ * `MTE_GRANULES_PER_PAGE / 2` tags and overflow the designated range size.
+ */
+static void test_two_ranges(struct kunit *test)
+{
+ struct test_data *td = test->priv;
+ unsigned long handle;
+ unsigned int i;
+ size_t r_len = 2;
+ unsigned char r_tags[2] = { 0xe, 0x0 };
+ unsigned short r_sizes[2];
+
+ for (i = 1; i < MTE_GRANULES_PER_PAGE; i++) {
+ r_sizes[0] = i;
+ r_sizes[1] = MTE_GRANULES_PER_PAGE - i;
+ mte_ranges_to_tags(r_tags, r_sizes, r_len, td->tags);
+ handle = compress_decompress_helper(test);
+ KUNIT_EXPECT_EQ(test, mte_storage_size(handle), 8);
+ }
+}
+
+/*
+ * Test that a very small number of tag ranges ends up compressed into 8 bytes.
+ */
+static void test_compress_simple(struct kunit *test)
+{
+ struct test_data *td = test->priv;
+ unsigned long handle;
+
+ memset(td->tags, 0, MTE_PAGE_TAG_STORAGE);
+ td->tags[0] = 0xa0;
+ td->tags[1] = 0x0a;
+
+ handle = compress_decompress_helper(test);
+ /* Tags are stored inline. */
+ KUNIT_EXPECT_EQ(test, mte_storage_size(handle), 8);
+ mte_release_handle(handle);
+}
+
+/*
+ * 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)
+{
+ struct test_data *td = test->priv;
+ unsigned long handle;
+
+ gen_tag_range_helper(td->tags, nranges);
+ handle = compress_decompress_helper(test);
+ KUNIT_EXPECT_EQ(test, mte_storage_size(handle), exp_size);
+ mte_release_handle(handle);
+}
+
+static size_t expected_size_from_ranges(unsigned int ranges)
+{
+#if defined CONFIG_ARM64_4K_PAGES
+ unsigned int range_exp[4] = { 6, 11, 23, 46 };
+#elif defined(CONFIG_ARM64_16K_PAGES)
+ unsigned int range_exp[6] = { 5, 9, 19, 39, 78, 157 };
+#elif defined(CONFIG_ARM64_64K_PAGES)
+ unsigned int range_exp[8] = { 4, 8, 17, 34, 68, 136, 273, 546 };
+#endif
+ unsigned int i;
+ size_t size = 8;
+
+ for (i = 0; i < ARRAY_SIZE(range_exp); i++) {
+ if (ranges <= range_exp[i])
+ return size;
+ size <<= 1;
+ }
+ return size;
+}
+
+/*
+ * 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 <= MTE_GRANULES_PER_PAGE; i++) {
+ exp_size = expected_size_from_ranges(i);
+ compress_range_helper(test, i, exp_size);
+ }
+}
+
+/*
+ * Test that invalid handles are ignored by mte_decompress().
+ */
+static void test_decompress_invalid(struct kunit *test)
+{
+ unsigned long handle1 = 0xeb0b0b010080402f;
+ unsigned long handle2 = 0x6b0b0b010080402f;
+ struct test_data *td = test->priv;
+
+ /* handle1 has bit 63 set to 1. */
+ KUNIT_EXPECT_FALSE(test, mte_decompress(handle1, td->dtags));
+ /*
+ * handle2 is an inline handle, but its largest_idx (bits 60..62)
+ * is out of bounds for the inline storage.
+ */
+ KUNIT_EXPECT_FALSE(test, mte_decompress(handle2, td->dtags));
+}
+
+/*
+ * Test that compressed inline tags cannot be confused with out-of-line
+ * pointers.
+ *
+ * Compressed values are written from bit 0 to bit 63, so the size of the last
+ * tag range initially ends up in the upper bits of the inline representation.
+ * Make sure mte_compress() rearranges the bits so that the resulting handle does
+ * not have 0b0111 as the upper four bits.
+ */
+static void test_upper_bits(struct kunit *test)
+{
+ struct test_data *td = test->priv;
+ unsigned long handle;
+ unsigned char r_tags[6] = { 7, 0, 7, 0, 7, 0 };
+ unsigned short r_sizes[6] = { 1, 1, 1, 1, 1, 1 };
+ size_t r_len;
+
+ /* Maximum number of ranges that can be encoded inline. */
+ r_len = IS_ENABLED(CONFIG_ARM64_4K_PAGES) ? 6 :
+ IS_ENABLED(CONFIG_ARM64_16K_PAGES) ? 5 :
+ 4;
+ /* Maximum range size possible, will be omitted. */
+ r_sizes[0] = MTE_GRANULES_PER_PAGE / 2 - 1;
+ /* A number close to r_sizes[0] that has most of its bits set. */
+ r_sizes[r_len - 1] = MTE_GRANULES_PER_PAGE - r_sizes[0] - r_len + 2;
+
+ mte_ranges_to_tags(r_tags, r_sizes, r_len, td->tags);
+ handle = compress_decompress_helper(test);
+ KUNIT_EXPECT_EQ(test, mte_storage_size(handle), 8);
+}
+
+static void mtecomp_dealloc_testdata(struct test_data *td)
+{
+ kfree(td->tags);
+ kfree(td->dtags);
+ kfree(td->r_sizes);
+ kfree(td->r_tags);
+}
+
+static int mtecomp_test_init(struct kunit *test)
+{
+ struct test_data *td;
+
+ td = kmalloc(sizeof(struct test_data), GFP_KERNEL);
+ if (!td)
+ return 1;
+ td->tags = kmalloc(MTE_PAGE_TAG_STORAGE, GFP_KERNEL);
+ if (!td->tags)
+ goto error;
+ td->dtags = kmalloc(MTE_PAGE_TAG_STORAGE, GFP_KERNEL);
+ if (!td->dtags)
+ goto error;
+ td->r_len = MTE_GRANULES_PER_PAGE;
+ td->r_sizes = kmalloc_array(MTE_GRANULES_PER_PAGE,
+ sizeof(unsigned short), GFP_KERNEL);
+ if (!td->r_sizes)
+ goto error;
+ td->r_tags = kmalloc(MTE_GRANULES_PER_PAGE, GFP_KERNEL);
+ if (!td->r_tags)
+ goto error;
+ test->priv = (void *)td;
+ return 0;
+error:
+ mtecomp_dealloc_testdata(td);
+ return 1;
+}
+
+static void mtecomp_test_exit(struct kunit *test)
+{
+ struct test_data *td = test->priv;
+
+ mtecomp_dealloc_testdata(td);
+}
+
+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_nonzero),
+ KUNIT_CASE(test_two_ranges),
+ KUNIT_CASE(test_compress_simple),
+ KUNIT_CASE(test_compress_ranges),
+ KUNIT_CASE(test_decompress_invalid),
+ KUNIT_CASE(test_upper_bits),
+ {}
+};
+
+static struct kunit_suite mtecomp_test_suite = {
+ .name = "mtecomp",
+ .init = mtecomp_test_init,
+ .exit = mtecomp_test_exit,
+ .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>");
--
2.42.0.609.gbb76f46606-goog