linux-kernel - [tip: x86/cache] fs/resctrl: Disable BMEC event configuration when mbm

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Message-ID: <175793564294.709179.14093747429137836945.tip-bot2@tip-bot2>
Date: Mon, 15 Sep 2025 11:27:22 -0000
From: "tip-bot2 for Babu Moger" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Reinette Chatre <reinette.chatre@...el.com>,
 Babu Moger <babu.moger@....com>, "Borislav Petkov (AMD)" <bp@...en8.de>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/cache] fs/resctrl: Disable BMEC event configuration when
 mbm_event mode is enabled

The following commit has been merged into the x86/cache branch of tip:

Commit-ID:     9f0209b857d2fc99c2a32bff1d7bfd54b314c29c
Gitweb:        https://git.kernel.org/tip/9f0209b857d2fc99c2a32bff1d7bfd54b314c29c
Author:        Babu Moger <babu.moger@....com>
AuthorDate:    Fri, 05 Sep 2025 16:34:29 -05:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Mon, 15 Sep 2025 12:48:19 +02:00

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>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com
---
 fs/resctrl/rdtgroup.c | 47 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 46 insertions(+), 1 deletion(-)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index bd4a115..0c404a1 100644
--- 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);
 		}
 	}