Commit

  a1cd99e700ec ("selftests/resctrl: Adjust effective L3 cache size with SNC enabled")

introduced the snc_nodes_per_l3_cache() function to detect the Intel
Sub-NUMA Clustering (SNC) feature by comparing #CPUs in node0 with #CPUs
sharing LLC with CPU0. The function was designed to return:
  (1) >1: SNC mode is enabled.
  (2)  1: SNC mode is not enabled or not supported.

However, on certain Hygon CPUs, #CPUs sharing LLC with CPU0 is actually
less than #CPUs in node0. This results in snc_nodes_per_l3_cache()
returning 0 (calculated as cache_cpus / node_cpus).

This leads to a division by zero error in get_cache_size():
  *cache_size /= snc_nodes_per_l3_cache();

Causing the resctrl selftest to fail with:
  "Floating point exception (core dumped)"

Fix the issue by ensuring snc_nodes_per_l3_cache() returns 1 when SNC
mode is not supported on the platform.

Fixes: a1cd99e700ec ("selftests/resctrl: Adjust effective L3 cache size with SNC enabled")
Signed-off-by: Xiaochen Shen <shenxiaochen@open-hieco.net>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
---
 tools/testing/selftests/resctrl/resctrlfs.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
index 195f04c4d158..b9c1bfb6cc02 100644
--- a/tools/testing/selftests/resctrl/resctrlfs.c
+++ b/tools/testing/selftests/resctrl/resctrlfs.c
@@ -243,6 +243,16 @@ int snc_nodes_per_l3_cache(void)
 		}
 		snc_mode = cache_cpus / node_cpus;
 
+		/*
+		 * On some platforms (e.g. Hygon),
+		 * cache_cpus < node_cpus, the calculated snc_mode is 0.
+		 *
+		 * Set snc_mode = 1 to indicate that SNC mode is not
+		 * supported on the platform.
+		 */
+		if (!snc_mode)
+			snc_mode = 1;
+
 		if (snc_mode > 1)
 			ksft_print_msg("SNC-%d mode discovered.\n", snc_mode);
 	}
-- 
2.47.3