linux-kernel - [PATCH v1] fs/resctrl: Add missing kconfig entry for CONFIG_RESCTRL_ASSIGN

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Message-ID: <20260113144952.47706-1-ben.horgan@arm.com>
Date: Tue, 13 Jan 2026 14:49:52 +0000
From: Ben Horgan <ben.horgan@....com>
To: linux-kernel@...r.kernel.org
Cc: tony.luck@...el.com,
	reinette.chatre@...el.com,
	Dave.Martin@....com,
	james.morse@....com,
	babu.moger@....com,
	bp@...en8.de,
	Ben Horgan <ben.horgan@....com>
Subject: [PATCH v1] fs/resctrl: Add missing kconfig entry for CONFIG_RESCTRL_ASSIGN_FIXED

The commit 3b497c3f4f04 ("fs/resctrl: Introduce the interface to display
monitoring modes") introduced CONFIG_RESCTRL_ASSIGN_FIXED but did not add
the kconfig entry. Add this.

Also, take the opportunity ensure that any user attempt to change the
assign mode fails from the resctrl code rather than delegating to the arch
specific code and let the user know by adding a message in last_cmd_status.

Fixes: 3b497c3f4f04 ("fs/resctrl: Introduce the interface to display monitoring modes")
Signed-off-by: Ben Horgan <ben.horgan@....com>
---
 fs/resctrl/Kconfig   | 8 ++++++++
 fs/resctrl/monitor.c | 6 ++++++
 2 files changed, 14 insertions(+)

diff --git a/fs/resctrl/Kconfig b/fs/resctrl/Kconfig
index 21671301bd8a..bdf9e11502fa 100644
--- a/fs/resctrl/Kconfig
+++ b/fs/resctrl/Kconfig
@@ -37,3 +37,11 @@ config RESCTRL_RMID_DEPENDS_ON_CLOSID
 	  Enabled by the architecture when the RMID values depend on the CLOSID.
 	  This causes the CLOSID allocator to search for CLOSID with clean
 	  RMID.
+
+config RESCTRL_ASSIGN_FIXED
+	bool
+	depends on RESCTRL_FS
+	help
+	 Enabled by the architecture when the counter assignment mode is not
+	 configurable. This ensures that counter assignment is not advertised as
+	 configurable and configuration attempts fail.
diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 572a9925bd6c..888e303c18a2 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -1434,6 +1434,12 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
 
 	rdt_last_cmd_clear();
 
+	if (IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED)) {
+		ret = -EINVAL;
+		rdt_last_cmd_puts("assign mode is not configurable\n");
+		goto out_unlock;
+	}
+
 	if (!strcmp(buf, "default")) {
 		enable = 0;
 	} else if (!strcmp(buf, "mbm_event")) {
-- 
2.43.0