[PATCH v6 1/2] selftests/resctrl: Fix CMT test failure when all cache bits are tested

[Richard Cheng <icheng@nvidia.com>]

The CMT test accepts any number of bits from 1 to the length of the full
cache bit mask via "-n". Since cmt_init() gives the default resource
group the inverse of the tested mask to keep other tasks out of the
tested cache portion.

When all bits are tested the inverse mask is empty. resctrl rejects an
empty mask with "Mask out of range" on systems that require at least one
bit to be set, cmt_init() fails and the test fails before taking any
measurement.

Only write the schemata of the default resource group when there're bits
left for it. When all bits are tested the default resource group keeps
its allocation.

Fixes: 7a214b4ec1c9 ("selftests/resctrl: Improve accuracy of cache occupancy test")
Signed-off-by: Richard Cheng <icheng@nvidia.com>
---
 tools/testing/selftests/resctrl/cmt_test.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/resctrl/cmt_test.c b/tools/testing/selftests/resctrl/cmt_test.c
index ccb6fe881a94..5d0bb27b7817 100644
--- a/tools/testing/selftests/resctrl/cmt_test.c
+++ b/tools/testing/selftests/resctrl/cmt_test.c
@@ -42,10 +42,13 @@ static int cmt_init(const struct resctrl_test *test,
 	if (ret)
 		return ret;
 
-	snprintf(schemata, sizeof(schemata), "%lx", ~param->mask & full_mask);
-	ret = write_schemata("", schemata, uparams->cpu, test->resource);
-	if (ret)
-		return ret;
+	/* No bits are left for the default group when all bits are tested. */
+	if (~param->mask & full_mask) {
+		snprintf(schemata, sizeof(schemata), "%lx", ~param->mask & full_mask);
+		ret = write_schemata("", schemata, uparams->cpu, test->resource);
+		if (ret)
+			return ret;
+	}
 
 	snprintf(schemata, sizeof(schemata), "%lx", param->mask);
 	ret = write_schemata(param->ctrlgrp, schemata, uparams->cpu, test->resource);
-- 
2.43.0