[PATCH 2/3] selftests/resctrl: Add L3_CAT_VALIDATE to check invalid CBMs

[Richard Cheng <icheng@nvidia.com>]

A CAT allocation is a CBM, and the kernel must refuse masks that can't
describe a valid allocation. Nothing in the suite check this.

Implement L3_CAT_VALIDATE, first confirm a valid full mask is accepted,
then write an empty mask and a mask with bits outside cbm_mask and
confirm each is refused. A mask below min_cbm_bits is also checked where
the platform needs more than one bit.

Signed-off-by: Richard Cheng <icheng@nvidia.com>
---
 tools/testing/selftests/resctrl/cat_test.c    | 79 +++++++++++++++++++
 tools/testing/selftests/resctrl/resctrl.h     |  1 +
 .../testing/selftests/resctrl/resctrl_tests.c |  1 +
 3 files changed, 81 insertions(+)

diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
index 16a947f1ed16..d236988916d9 100644
--- a/tools/testing/selftests/resctrl/cat_test.c
+++ b/tools/testing/selftests/resctrl/cat_test.c
@@ -603,3 +603,82 @@ struct resctrl_test l3_cat_occup_test = {
 	.run_test = cat_occup_run_test,
 	.cleanup = cat_occup_test_cleanup,
 };
+
+/*
+ * L3_CAT_VALIDATE - Verify the kernel rejects invalid L3 CBM writes.
+ *
+ * CAT allocation accepts a Capacity Bit Mask (CBM). The kernel must reject
+ * masks that cannot represent a valid allocation: an empty mask, a mask with
+ * bits outside cbm_mask, or (where the platform requires it) a mask with
+ * fewer than min_cbm_bits bits. A rejected schemata write makes
+ * write_schemata() return non-zero, which is the signal this test checks.
+ */
+static int cat_validate_run_test(const struct resctrl_test *test,
+				 const struct user_params *uparams)
+{
+	unsigned long full_mask, bad_mask;
+	unsigned int min_cbm_bits, start;
+	char schemata[64];
+	int count_of_bits, ret;
+
+	ret = get_full_cbm(test->resource, &full_mask);
+	if (ret)
+		return ret;
+
+	ret = resource_info_unsigned_get(test->resource, "min_cbm_bits",
+					 &min_cbm_bits);
+	if (ret)
+		return ret;
+
+	count_of_bits = count_bits(full_mask);
+
+	/* A valid full CBM must be accepted */
+	snprintf(schemata, sizeof(schemata), "%lx", full_mask);
+	if (write_schemata("", schemata, uparams->cpu, test->resource)) {
+		ksft_print_msg("Valid CBM 0x%lx was rejected\n", full_mask);
+		return 1;
+	}
+
+	/* An empty mask must be rejected. */
+	if (!write_schemata("", "0", uparams->cpu, test->resource)) {
+		ksft_print_msg("Empty CBM was accepted, must be rejected\n");
+		return 1;
+	}
+
+	/* A mask with a bit outside cbm_mask must be rejected. */
+	bad_mask = full_mask | (1UL << count_of_bits);
+	snprintf(schemata, sizeof(schemata), "%lx", bad_mask);
+	if (!write_schemata("", schemata, uparams->cpu, test->resource)) {
+		ksft_print_msg("Out-of-range CBM 0x%lx was accepted, must be rejected\n",
+			       bad_mask);
+		return 1;
+	}
+
+	/*
+	 * A mask with fewer than min_cbm_bits bits must be rejected. When
+	 * min_cbm_bits is 1 the only sub-minimum mask is the empty mask
+	 * This case only applies when the platform requires more contiguous bits.
+	 */
+	if (min_cbm_bits > 1) {
+		count_contiguous_bits(full_mask, &start);
+		bad_mask = create_bit_mask(start, min_cbm_bits - 1);
+		snprintf(schemata, sizeof(schemata), "%lx", bad_mask);
+		if (!write_schemata("", schemata, uparams->cpu, test->resource)) {
+			ksft_print_msg("CBM 0x%lx with too few bits was accepted\n",
+				       bad_mask);
+			return 1;
+		}
+	}
+
+	ksft_print_msg("Pass: CAT rejects invalid CBM writes\n");
+
+	return 0;
+}
+
+struct resctrl_test l3_cat_validate_test = {
+	.name = "L3_CAT_VALIDATE",
+	.group = "CAT",
+	.resource = "L3",
+	.feature_check = test_resource_feature_check,
+	.run_test = cat_validate_run_test,
+};
diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
index ce3abf0bdac2..e2e3cf7833bc 100644
--- a/tools/testing/selftests/resctrl/resctrl.h
+++ b/tools/testing/selftests/resctrl/resctrl.h
@@ -248,6 +248,7 @@ extern struct resctrl_test mba_test;
 extern struct resctrl_test cmt_test;
 extern struct resctrl_test l3_cat_test;
 extern struct resctrl_test l3_cat_occup_test;
+extern struct resctrl_test l3_cat_validate_test;
 extern struct resctrl_test l3_noncont_cat_test;
 extern struct resctrl_test l2_noncont_cat_test;
 
diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
index 324a60818aa1..66739e96f33c 100644
--- a/tools/testing/selftests/resctrl/resctrl_tests.c
+++ b/tools/testing/selftests/resctrl/resctrl_tests.c
@@ -20,6 +20,7 @@ static struct resctrl_test *resctrl_tests[] = {
 	&cmt_test,
 	&l3_cat_test,
 	&l3_cat_occup_test,
+	&l3_cat_validate_test,
 	&l3_noncont_cat_test,
 	&l2_noncont_cat_test,
 };
-- 
2.43.0