[PATCH v2 1/2] selftests/resctrl: Add L3_CBM_VALIDATE to check CBM writes

[Richard Cheng <icheng@nvidia.com>]

Add L3_CBM_VALIDATE to verify that resctrl enforces the L3 CBM rules
advertised by cbm_mask and min_cbm_bits.

Confirm that the full mask is accepted. Check the empty mask according
to min_cbm_bits, and confirm that out-of-range and undersized masks are
rejected.

This catches inconsistencies between the advertised capabilities and
schemata validation.

Signed-off-by: Richard Cheng <icheng@nvidia.com>
---
Changelog:

v1 -> v2:
    - Rename L3_CAT_VALIDATE to L3_CBM_VALIDATE
    - Handle empty CBMs according to min_cbm_bits
    - Check count_contiguous_bits() before using its result
    - Use KSFT_FAIL and reverse-fir-tree ordering
    - Use a 64-bit out-of-range mask

Best regards,
Richard Cheng.
---
 tools/testing/selftests/resctrl/cat_test.c    | 91 +++++++++++++++++++
 tools/testing/selftests/resctrl/resctrl.h     |  1 +
 .../testing/selftests/resctrl/resctrl_tests.c |  1 +
 3 files changed, 93 insertions(+)

diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
index 371a2f26dc47..a06c57954740 100644
--- a/tools/testing/selftests/resctrl/cat_test.c
+++ b/tools/testing/selftests/resctrl/cat_test.c
@@ -357,6 +357,89 @@ static bool noncont_cat_feature_check(const struct resctrl_test *test)
 	return resource_info_file_exists(test->resource, "sparse_masks");
 }
 
+/*
+ * L3_CBM_VALIDATE - Verify L3 CBM write validation.
+ *
+ * A full CBM must be accepted. An empty CBM is valid only when min_cbm_bits
+ * is zero. Masks with bits outside cbm_mask or fewer than min_cbm_bits must
+ * be rejected.
+ */
+static int cbm_validate_run_test(const struct resctrl_test *test,
+				 const struct user_params *uparams)
+{
+	unsigned int min_cbm_bits, contiguous_bits;
+	unsigned long long invalid_mask;
+	unsigned int count_of_bits;
+	unsigned long full_mask;
+	unsigned int start;
+	char schemata[64];
+	int 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 KSFT_FAIL;
+	}
+
+	ret = write_schemata("", "0", uparams->cpu, test->resource);
+	if (min_cbm_bits && !ret) {
+		ksft_print_msg("Empty CBM was accepted, must be rejected\n");
+		return KSFT_FAIL;
+	}
+	if (!min_cbm_bits && ret) {
+		ksft_print_msg("Empty CBM was rejected, must be accepted\n");
+		return KSFT_FAIL;
+	}
+
+	/* A mask with a bit outside cbm_mask must be rejected. */
+	invalid_mask = (unsigned long long)full_mask | (1ULL << count_of_bits);
+	snprintf(schemata, sizeof(schemata), "%llx", invalid_mask);
+	if (!write_schemata("", schemata, uparams->cpu, test->resource)) {
+		ksft_print_msg("Out-of-range CBM 0x%llx was accepted, must be rejected\n",
+			       invalid_mask);
+		return KSFT_FAIL;
+	}
+
+	/*
+	 * When min_cbm_bits is greater than one, a non-empty mask with fewer
+	 * bits must be rejected.
+	 */
+	if (min_cbm_bits > 1) {
+		contiguous_bits = count_contiguous_bits(full_mask, &start);
+		if (contiguous_bits < min_cbm_bits) {
+			ksft_print_msg("Full CBM has %u contiguous bits, fewer than "
+				       "min_cbm_bits=%u\n",
+				       contiguous_bits, min_cbm_bits);
+			return KSFT_FAIL;
+		}
+
+		invalid_mask = create_bit_mask(start, min_cbm_bits - 1);
+		snprintf(schemata, sizeof(schemata), "%llx", invalid_mask);
+		if (!write_schemata("", schemata, uparams->cpu,
+				    test->resource)) {
+			ksft_print_msg("CBM 0x%llx with too few bits was accepted\n",
+				       invalid_mask);
+			return KSFT_FAIL;
+		}
+	}
+
+	ksft_print_msg("Pass: L3 CBM writes were validated correctly\n");
+
+	return 0;
+}
+
 struct resctrl_test l3_cat_test = {
 	.name = "L3_CAT",
 	.group = "CAT",
@@ -366,6 +449,14 @@ struct resctrl_test l3_cat_test = {
 	.cleanup = cat_test_cleanup,
 };
 
+struct resctrl_test l3_cbm_validate_test = {
+	.name = "L3_CBM_VALIDATE",
+	.group = "CAT",
+	.resource = "L3",
+	.feature_check = test_resource_feature_check,
+	.run_test = cbm_validate_run_test,
+};
+
 struct resctrl_test l3_noncont_cat_test = {
 	.name = "L3_NONCONT_CAT",
 	.group = "CAT",
diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
index 175101022bf3..a6fc688ed997 100644
--- a/tools/testing/selftests/resctrl/resctrl.h
+++ b/tools/testing/selftests/resctrl/resctrl.h
@@ -240,6 +240,7 @@ extern struct resctrl_test mbm_test;
 extern struct resctrl_test mba_test;
 extern struct resctrl_test cmt_test;
 extern struct resctrl_test l3_cat_test;
+extern struct resctrl_test l3_cbm_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 dbcd5eea9fbc..57a4d0815b67 100644
--- a/tools/testing/selftests/resctrl/resctrl_tests.c
+++ b/tools/testing/selftests/resctrl/resctrl_tests.c
@@ -19,6 +19,7 @@ static struct resctrl_test *resctrl_tests[] = {
 	&mba_test,
 	&cmt_test,
 	&l3_cat_test,
+	&l3_cbm_validate_test,
 	&l3_noncont_cat_test,
 	&l2_noncont_cat_test,
 };
-- 
2.53.0