[PATCH RFC v2 19/19] selftests/resctrl: Add MB emulation test for ARM MPAM

[Fenghua Yu <fenghuay@nvidia.com>]

Add a kselftest that exercises MB control emulation on ARM MPAM:
info/MB/control_mode, the nested MB_NODE control under
info/MB/schemata/MB/, and schemata visibility when switching legacy
(MB:) and native (MB_NODE:) modes. The info/ schemata tree stays nested
across the switch.

Signed-off-by: Fenghua Yu <fenghuay@nvidia.com>
---
 .../selftests/resctrl/mb_emulation_test.c     | 314 ++++++++++++++++++
 tools/testing/selftests/resctrl/resctrl.h     |   1 +
 .../testing/selftests/resctrl/resctrl_tests.c |   1 +
 3 files changed, 316 insertions(+)
 create mode 100644 tools/testing/selftests/resctrl/mb_emulation_test.c

diff --git a/tools/testing/selftests/resctrl/mb_emulation_test.c b/tools/testing/selftests/resctrl/mb_emulation_test.c
new file mode 100644
index 000000000000..845aa46fd092
--- /dev/null
+++ b/tools/testing/selftests/resctrl/mb_emulation_test.c
@@ -0,0 +1,314 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * MB (memory bandwidth) control emulation test (ARM MPAM)
+ *
+ * Exercises info/MB/control_mode, the nested MB_NODE control under
+ * info/MB/schemata/MB/, and schemata visibility when switching between
+ * legacy (MB:) and native (MB_NODE:) modes.
+ */
+#include <fcntl.h>
+#include <limits.h>
+
+#include "resctrl.h"
+
+#define MB_INFO			INFO_PATH "/MB"
+#define MB_MODE_PATH		MB_INFO "/control_mode"
+#define MB_SCHEMATA_DIR		MB_INFO "/schemata"
+#define MB_CTRL_PATH		MB_SCHEMATA_DIR "/MB"
+#define MB_NODE_NESTED_PATH	MB_CTRL_PATH "/MB_NODE"
+#define MB_NODE_SIBLING_PATH	MB_SCHEMATA_DIR "/MB_NODE"
+#define ROOT_SCHEMATA_PATH	RESCTRL_PATH "/schemata"
+
+static int read_file(const char *path, char *buf, size_t buflen)
+{
+	ssize_t ret;
+	int fd, n;
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0)
+		return -errno;
+
+	ret = read(fd, buf, buflen - 1);
+	close(fd);
+	if (ret < 0)
+		return -errno;
+
+	n = (int)ret;
+	while (n > 0 && (buf[n - 1] == '\n' || buf[n - 1] == ' '))
+		n--;
+	buf[n] = '\0';
+
+	return 0;
+}
+
+static bool path_is_dir(const char *path)
+{
+	struct stat st;
+
+	if (stat(path, &st))
+		return false;
+
+	return S_ISDIR(st.st_mode);
+}
+
+static int mb_read_mode(char *buf, size_t len)
+{
+	return read_file(MB_MODE_PATH, buf, len);
+}
+
+static int mb_write_mode(const char *mode)
+{
+	char msg[32];
+	int fd, ret, len;
+
+	len = snprintf(msg, sizeof(msg), "%s\n", mode);
+	if (len < 0 || len >= (int)sizeof(msg))
+		return -EINVAL;
+
+	fd = open(MB_MODE_PATH, O_WRONLY);
+	if (fd < 0)
+		return -errno;
+
+	ret = write(fd, msg, len) == len ? 0 : -errno;
+	close(fd);
+
+	return ret;
+}
+
+static bool mb_mode_active_is(const char *mode_text, const char *mode)
+{
+	char pattern[32];
+
+	snprintf(pattern, sizeof(pattern), "[%s]", mode);
+	return strstr(mode_text, pattern);
+}
+
+static int mb_read_root_schemata(char *buf, size_t len)
+{
+	return read_file(ROOT_SCHEMATA_PATH, buf, len);
+}
+
+/*
+ * resctrl right-aligns schemata names with leading whitespace, so a control
+ * line looks like "             MB:0=100...". Treat prefix as matching when it
+ * appears at the start of a line, ignoring any leading spaces or tabs.
+ */
+static const char *schemata_find_line(const char *schemata, const char *prefix)
+{
+	const char *p;
+
+	if (!schemata || !prefix)
+		return NULL;
+
+	for (p = strstr(schemata, prefix); p; p = strstr(p + 1, prefix)) {
+		const char *q = p;
+
+		while (q > schemata && (q[-1] == ' ' || q[-1] == '\t'))
+			q--;
+
+		if (q == schemata || q[-1] == '\n')
+			return p;
+	}
+
+	return NULL;
+}
+
+static bool schemata_has_prefix(const char *schemata, const char *prefix)
+{
+	return schemata_find_line(schemata, prefix);
+}
+
+static int mb_expect_nested_hierarchy(const char *why)
+{
+	if (!path_is_dir(MB_NODE_NESTED_PATH) || path_is_dir(MB_NODE_SIBLING_PATH)) {
+		ksft_print_msg("%s: MB_NODE should be nested, nested=%d sibling=%d\n",
+			       why, path_is_dir(MB_NODE_NESTED_PATH),
+			       path_is_dir(MB_NODE_SIBLING_PATH));
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int mb_test_mode_read(void)
+{
+	char mode[64];
+	int ret;
+
+	ret = mb_read_mode(mode, sizeof(mode));
+	if (ret)
+		return ret;
+
+	if (!mb_mode_active_is(mode, "legacy") && !mb_mode_active_is(mode, "native")) {
+		ksft_print_msg("mode file has no active mode: '%s'\n", mode);
+		return -EINVAL;
+	}
+
+	ksft_print_msg("mode file: %s\n", mode);
+	return 0;
+}
+
+static int mb_test_schemata_visibility(bool expect_mb_line, const char *mode)
+{
+	char schemata[4096];
+	bool has_mb, has_mb_node;
+	int ret;
+
+	ret = mb_read_root_schemata(schemata, sizeof(schemata));
+	if (ret)
+		return ret;
+
+	has_mb = schemata_has_prefix(schemata, "MB:");
+	has_mb_node = schemata_has_prefix(schemata, "MB_NODE:");
+
+	if (expect_mb_line) {
+		if (!has_mb) {
+			ksft_print_msg("%s: expected MB: line in schemata\n", mode);
+			return -EINVAL;
+		}
+		if (has_mb_node) {
+			ksft_print_msg("%s: MB_NODE: line should be hidden in schemata\n",
+				       mode);
+			return -EINVAL;
+		}
+	} else {
+		if (has_mb) {
+			ksft_print_msg("%s: MB: line should be hidden in schemata\n",
+				       mode);
+			return -EINVAL;
+		}
+		if (!has_mb_node) {
+			ksft_print_msg("%s: expected MB_NODE: line in schemata\n",
+				       mode);
+			return -EINVAL;
+		}
+	}
+
+	ksft_print_msg("switched to %s: schemata MB:%d MB_NODE:%d\n",
+		       mode, has_mb, has_mb_node);
+	return 0;
+}
+
+static int mb_restore_mode(const char *orig_mode)
+{
+	if (mb_mode_active_is(orig_mode, "legacy"))
+		return mb_write_mode("legacy");
+	if (mb_mode_active_is(orig_mode, "native"))
+		return mb_write_mode("native");
+
+	return 0;
+}
+
+static int mb_verify_active_mode(const char *mode)
+{
+	char buf[64];
+	int ret;
+
+	ret = mb_read_mode(buf, sizeof(buf));
+	if (ret)
+		return ret;
+
+	if (!mb_mode_active_is(buf, mode)) {
+		ksft_print_msg("mode switch to %s failed, mode file: '%s'\n",
+			       mode, buf);
+		return -EINVAL;
+	}
+
+	ksft_print_msg("switched to %s: mode file='%s'\n", mode, buf);
+	return 0;
+}
+
+/*
+ * Switch to @mode and verify the mode file, the nested info/MB/schemata
+ * layout (unchanged by the switch), and root schemata visibility.
+ */
+static int mb_switch_and_check(const char *mode)
+{
+	bool legacy = !strcmp(mode, "legacy");
+	int ret;
+
+	ksft_print_msg("--- switching to %s mode ---\n", mode);
+
+	ret = mb_write_mode(mode);
+	if (ret) {
+		ksft_print_msg("failed to write %s mode\n", mode);
+		return ret;
+	}
+
+	ret = mb_verify_active_mode(mode);
+	if (ret)
+		return ret;
+
+	ret = mb_expect_nested_hierarchy(mode);
+	if (ret)
+		return ret;
+
+	return mb_test_schemata_visibility(legacy, mode);
+}
+
+static int mb_emulation_run_test(const struct resctrl_test *test,
+				 const struct user_params *uparams)
+{
+	char orig_mode[64];
+	int ret;
+
+	(void)test;
+	(void)uparams;
+
+	ret = mb_expect_nested_hierarchy("initial");
+	if (ret)
+		return ret;
+
+	ret = mb_read_mode(orig_mode, sizeof(orig_mode));
+	if (ret) {
+		ksft_print_msg("failed to read %s\n", MB_MODE_PATH);
+		return ret;
+	}
+
+	ret = mb_test_mode_read();
+	if (ret)
+		goto out_restore;
+
+	/* Cycle legacy -> native -> legacy, checking each transition. */
+	ret = mb_switch_and_check("legacy");
+	if (ret)
+		goto out_restore;
+
+	ret = mb_switch_and_check("native");
+	if (ret)
+		goto out_restore;
+
+	ret = mb_switch_and_check("legacy");
+	if (ret)
+		goto out_restore;
+
+out_restore:
+	if (mb_restore_mode(orig_mode))
+		ksft_print_msg("warning: failed to restore original mode\n");
+
+	return ret;
+}
+
+static bool mb_emulation_feature_check(const struct resctrl_test *test)
+{
+	(void)test;
+
+	if (!resctrl_resource_exists("MB"))
+		return false;
+
+	if (!resource_info_file_exists("MB", "control_mode"))
+		return false;
+
+	if (!path_is_dir(MB_SCHEMATA_DIR) || !path_is_dir(MB_CTRL_PATH))
+		return false;
+
+	return path_is_dir(MB_NODE_NESTED_PATH);
+}
+
+struct resctrl_test mb_emulation_test = {
+	.name = "mb_emulation",
+	.group = "mb",
+	.resource = "MB",
+	.feature_check = mb_emulation_feature_check,
+	.run_test = mb_emulation_run_test,
+};
diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
index 175101022bf3..ad1c17c0b0bf 100644
--- a/tools/testing/selftests/resctrl/resctrl.h
+++ b/tools/testing/selftests/resctrl/resctrl.h
@@ -242,5 +242,6 @@ extern struct resctrl_test cmt_test;
 extern struct resctrl_test l3_cat_test;
 extern struct resctrl_test l3_noncont_cat_test;
 extern struct resctrl_test l2_noncont_cat_test;
+extern struct resctrl_test mb_emulation_test;
 
 #endif /* RESCTRL_H */
diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
index dbcd5eea9fbc..593f0ca5251b 100644
--- a/tools/testing/selftests/resctrl/resctrl_tests.c
+++ b/tools/testing/selftests/resctrl/resctrl_tests.c
@@ -17,6 +17,7 @@ volatile int *value_sink = &sink_target;
 static struct resctrl_test *resctrl_tests[] = {
 	&mbm_test,
 	&mba_test,
+	&mb_emulation_test,
 	&cmt_test,
 	&l3_cat_test,
 	&l3_noncont_cat_test,
-- 
2.53.0