linux-kernel - [PATCH] fs/resctrl: Fix MBM events being unconditionally enabled in mbm

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Message-ID: <6082147693739c4514e4a650a62f805956331d51.1759263540.git.babu.moger@amd.com>
Date: Tue, 30 Sep 2025 15:26:17 -0500
From: Babu Moger <babu.moger@....com>
To: <tony.luck@...el.com>, <reinette.chatre@...el.com>, <Dave.Martin@....com>,
	<james.morse@....com>, <dave.hansen@...ux.intel.com>, <bp@...en8.de>
CC: <babu.moger@....com>, <kas@...nel.org>, <rick.p.edgecombe@...el.com>,
	<linux-kernel@...r.kernel.org>, <x86@...nel.org>,
	<linux-coco@...ts.linux.dev>, <kvm@...r.kernel.org>
Subject: [PATCH] fs/resctrl: Fix MBM events being unconditionally enabled in mbm_event mode

resctrl features can be enabled or disabled using boot-time kernel
parameters. To turn off the memory bandwidth events (mbmtotal and
mbmlocal), users need to pass the following parameter to the kernel:
"rdt=!mbmtotal,!mbmlocal".

Found that memory bandwidth events (mbmtotal and mbmlocal) cannot be
disabled when mbm_event mode is enabled. resctrl_mon_resource_init()
unconditionally enables these events without checking if the underlying
hardware supports them.

Remove the unconditional enablement of MBM features in
resctrl_mon_resource_init() to fix the problem. The hardware support
verification is already done in get_rdt_mon_resources().

Fixes: 13390861b426 ("x86,fs/resctrl: Detect Assignable Bandwidth Monitoring feature details")
Signed-off-by: Babu Moger <babu.moger@....com>
---
Patch is created on top of latest tip/master(6.17.0-rc7):
707007037fc6 (tip/master) Merge branch into tip/master: 'x86/tdx'
---
 fs/resctrl/monitor.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 4076336fbba6..572a9925bd6c 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -1782,15 +1782,13 @@ int resctrl_mon_resource_init(void)
 		mba_mbps_default_event = QOS_L3_MBM_TOTAL_EVENT_ID;
 
 	if (r->mon.mbm_cntr_assignable) {
-		if (!resctrl_is_mon_event_enabled(QOS_L3_MBM_TOTAL_EVENT_ID))
-			resctrl_enable_mon_event(QOS_L3_MBM_TOTAL_EVENT_ID);
-		if (!resctrl_is_mon_event_enabled(QOS_L3_MBM_LOCAL_EVENT_ID))
-			resctrl_enable_mon_event(QOS_L3_MBM_LOCAL_EVENT_ID);
-		mon_event_all[QOS_L3_MBM_TOTAL_EVENT_ID].evt_cfg = r->mon.mbm_cfg_mask;
-		mon_event_all[QOS_L3_MBM_LOCAL_EVENT_ID].evt_cfg = r->mon.mbm_cfg_mask &
-								   (READS_TO_LOCAL_MEM |
-								    READS_TO_LOCAL_S_MEM |
-								    NON_TEMP_WRITE_TO_LOCAL_MEM);
+		if (resctrl_is_mon_event_enabled(QOS_L3_MBM_TOTAL_EVENT_ID))
+			mon_event_all[QOS_L3_MBM_TOTAL_EVENT_ID].evt_cfg = r->mon.mbm_cfg_mask;
+		if (resctrl_is_mon_event_enabled(QOS_L3_MBM_LOCAL_EVENT_ID))
+			mon_event_all[QOS_L3_MBM_LOCAL_EVENT_ID].evt_cfg = r->mon.mbm_cfg_mask &
+									   (READS_TO_LOCAL_MEM |
+									    READS_TO_LOCAL_S_MEM |
+									    NON_TEMP_WRITE_TO_LOCAL_MEM);
 		r->mon.mbm_assign_on_mkdir = true;
 		resctrl_file_fflags_init("num_mbm_cntrs",
 					 RFTYPE_MON_INFO | RFTYPE_RES_CACHE);
-- 
2.34.1