fs/resctrl: Disable BMEC event configuration when mbm_event mode is enabled

The BMEC (Bandwidth Monitoring Event Configuration) feature enables per-domain
event configuration. With BMEC the MBM events are configured using the
mbm_total_bytes_config or mbm_local_bytes_config files in

  /sys/fs/resctrl/info/L3_MON/

and the per-domain event configuration affects all monitor resource groups.

The mbm_event counter assignment mode enables counters to be assigned to RMID
(i.e. a monitor resource group), event pairs, with potentially unique event
configurations associated with every counter.

There may be systems that support both BMEC and mbm_event counter assignment
mode, but resctrl supporting both concurrently will present a conflicting
interface to the user with both per-domain and per RMID, event configurations
active at the same time.

The mbm_event counter assignment provides most flexibility to user space
and aligns with Arm's counter support. On systems that support both,
disable BMEC event configuration when mbm_event mode is enabled by hiding
the mbm_total_bytes_config or mbm_local_bytes_config files when mbm_event
mode is enabled. Ensure mon_features always displays accurate information
about monitor features.

Suggested-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index bd4a115ffea188572256c79a0b168c5e9afd34e4..0c404a159d455840b56dce69571ecadeb3b214dd 100644 (file)
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -1150,7 +1150,8 @@ static int rdt_mon_features_show(struct kernfs_open_file *of,
                if (mevt->rid != r->rid || !mevt->enabled)
                        continue;
                seq_printf(seq, "%s\n", mevt->name);
-               if (mevt->configurable)
+               if (mevt->configurable &&
+                   !resctrl_arch_mbm_cntr_assign_enabled(r))
                        seq_printf(seq, "%s_config\n", mevt->name);
        }
 
@@ -1799,6 +1800,44 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,
        return ret ?: nbytes;
 }
 
+/*
+ * resctrl_bmec_files_show() — Controls the visibility of BMEC-related resctrl
+ * files. When @show is true, the files are displayed; when false, the files
+ * are hidden.
+ * Don't treat kernfs_find_and_get failure as an error, since this function may
+ * be called regardless of whether BMEC is supported or the event is enabled.
+ */
+static void resctrl_bmec_files_show(struct rdt_resource *r, struct kernfs_node *l3_mon_kn,
+                                   bool show)
+{
+       struct kernfs_node *kn_config, *mon_kn = NULL;
+       char name[32];
+
+       if (!l3_mon_kn) {
+               sprintf(name, "%s_MON", r->name);
+               mon_kn = kernfs_find_and_get(kn_info, name);
+               if (!mon_kn)
+                       return;
+               l3_mon_kn = mon_kn;
+       }
+
+       kn_config = kernfs_find_and_get(l3_mon_kn, "mbm_total_bytes_config");
+       if (kn_config) {
+               kernfs_show(kn_config, show);
+               kernfs_put(kn_config);
+       }
+
+       kn_config = kernfs_find_and_get(l3_mon_kn, "mbm_local_bytes_config");
+       if (kn_config) {
+               kernfs_show(kn_config, show);
+               kernfs_put(kn_config);
+       }
+
+       /* Release the reference only if it was acquired */
+       if (mon_kn)
+               kernfs_put(mon_kn);
+}
+
 /* rdtgroup information files for one cache resource. */
 static struct rftype res_common_files[] = {
        {
@@ -2267,6 +2306,12 @@ static int rdtgroup_mkdir_info_resdir(void *priv, char *name,
                        ret = resctrl_mkdir_event_configs(r, kn_subdir);
                        if (ret)
                                return ret;
+                       /*
+                        * Hide BMEC related files if mbm_event mode
+                        * is enabled.
+                        */
+                       if (resctrl_arch_mbm_cntr_assign_enabled(r))
+                               resctrl_bmec_files_show(r, kn_subdir, false);
                }
        }