linux-kernel - [PATCH v15 32/34] fs/resctrl: Disable BMEC event configuration when mbm

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Message-ID: <6aee8abeef1bdc5b88f8c3142a702a9d683f5f66.1752013061.git.babu.moger@amd.com>
Date: Tue, 8 Jul 2025 17:17:41 -0500
From: Babu Moger <babu.moger@....com>
To: <corbet@....net>, <tony.luck@...el.com>, <reinette.chatre@...el.com>,
	<james.morse@....com>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<bp@...en8.de>, <dave.hansen@...ux.intel.com>
CC: <Dave.Martin@....com>, <x86@...nel.org>, <hpa@...or.com>,
	<akpm@...ux-foundation.org>, <paulmck@...nel.org>, <rostedt@...dmis.org>,
	<Neeraj.Upadhyay@....com>, <david@...hat.com>, <arnd@...db.de>,
	<fvdl@...gle.com>, <seanjc@...gle.com>, <jpoimboe@...nel.org>,
	<pawan.kumar.gupta@...ux.intel.com>, <xin@...or.com>,
	<manali.shukla@....com>, <babu.moger@....com>, <tao1.su@...ux.intel.com>,
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	<gautham.shenoy@....com>, <chang.seok.bae@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<peternewman@...gle.com>, <eranian@...gle.com>
Subject: [PATCH v15 32/34] 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@...el.com>
Signed-off-by: Babu Moger <babu.moger@....com>
---
v15: Updated the changelog.
     Moved resctrl_bmec_files_show() inside rdtgroup_mkdir_info_resdir().
     Removed the unnecessary kernfs_get() call.

v14: Updated the changelog for change in mbm_assign_modes.
     Added check in rdt_mon_features_show to hide bmec related feature.

v13: New patch to hide BMEC related files.
---
 fs/resctrl/rdtgroup.c | 39 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index b26baca389bb..d73057b96d1d 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -1152,7 +1152,8 @@ 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);
 	}
 
@@ -1801,6 +1802,36 @@ 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.
+ */
+static void resctrl_bmec_files_show(struct rdt_resource *r, bool show)
+{
+	struct kernfs_node *kn_config, *l3_mon_kn;
+	char name[32];
+
+	sprintf(name, "%s_MON", r->name);
+	l3_mon_kn = kernfs_find_and_get(kn_info, name);
+	if (!l3_mon_kn)
+		return;
+
+	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);
+	}
+
+	kernfs_put(l3_mon_kn);
+}
+
 static int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
 					struct seq_file *s, void *v)
 {
@@ -2659,6 +2690,12 @@ 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, false);
 		}
 	}
 
-- 
2.34.1