linux-kernel - [v4 PATCH 1/1] x86/resctrl: Add "*" shorthand to set io

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Message-ID: <20260125171752.3374930-2-atomlin@atomlin.com>
Date: Sun, 25 Jan 2026 12:17:52 -0500
From: Aaron Tomlin <atomlin@...mlin.com>
To: tony.luck@...el.com,
	reinette.chatre@...el.com,
	Dave.Martin@....com,
	james.morse@....com,
	babu.moger@....com,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com
Cc: dave.martin@....com,
	sean@...e.io,
	neelx@...e.com,
	mproche@...il.com,
	chjohnst@...il.com,
	linux-kernel@...r.kernel.org
Subject: [v4 PATCH 1/1] x86/resctrl: Add "*" shorthand to set io_alloc CBM for all domains

Introduce a wildcard domain ID selector "*" for the io_alloc_cbm
interface. This allows a user to update the Capacity Bitmask (CBM)
across all cache domains in a single operation.

Currently, configuring io_alloc_cbm requires an explicit ID for each
domain, which is cumbersome on systems with high core counts and
numerous cache clusters. Supporting a wildcard selector simplifies
automation and management tasks.

For example, a user can now write "*=0" to the io_alloc_cbm file to
program every domain to the hardware-defined minimum CBM. Note that the
value provided must still adhere to the constraints defined in the
resource's min_cbm_bits.

Signed-off-by: Aaron Tomlin <atomlin@...mlin.com>
---
 Documentation/filesystems/resctrl.rst |  8 ++++++++
 fs/resctrl/ctrlmondata.c              | 20 +++++++++++++++++---
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index 8c8ce678148a..734aba0d19fd 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -215,6 +215,14 @@ related to allocation:
 			# cat /sys/fs/resctrl/info/L3/io_alloc_cbm
 			0=00ff;1=000f
 
+		Set each CBM to a specified value.
+
+		An ID of "*" configures all domains with the provided CBM.
+
+		Example::
+
+			# echo "*=0" > /sys/fs/resctrl/info/L3/io_alloc_cbm
+
 		When CDP is enabled "io_alloc_cbm" associated with the CDP_DATA and CDP_CODE
 		resources may reflect the same values. For example, values read from and
 		written to /sys/fs/resctrl/info/L3DATA/io_alloc_cbm may be reflected by
diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
index b2d178d3556e..f5fb74a7668a 100644
--- a/fs/resctrl/ctrlmondata.c
+++ b/fs/resctrl/ctrlmondata.c
@@ -873,21 +873,31 @@ static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
 	struct rdt_ctrl_domain *d;
 	char *dom = NULL, *id;
 	unsigned long dom_id;
+	bool update_all;
 
 next:
 	if (!line || line[0] == '\0')
 		return 0;
 
+	update_all = false;
 	dom = strsep(&line, ";");
 	id = strsep(&dom, "=");
-	if (!dom || kstrtoul(id, 10, &dom_id)) {
+
+	if (id && !strcmp(id, "*")) {
+		update_all = true;
+	} else if (!dom || kstrtoul(id, 10, &dom_id)) {
 		rdt_last_cmd_puts("Missing '=' or non-numeric domain\n");
 		return -EINVAL;
 	}
 
 	dom = strim(dom);
+	if (update_all && !dom) {
+		rdt_last_cmd_puts("Missing '=' after '*'\n");
+		return -EINVAL;
+	}
+
 	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
-		if (d->hdr.id == dom_id) {
+		if (update_all || d->hdr.id == dom_id) {
 			data.buf = dom;
 			data.mode = RDT_MODE_SHAREABLE;
 			data.closid = closid;
@@ -903,10 +913,14 @@ static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
 				       &d->staged_config[s->conf_type],
 				       sizeof(d->staged_config[0]));
 			}
-			goto next;
+			if (!update_all)
+				goto next;
 		}
 	}
 
+	if (update_all)
+		goto next;
+
 	return -EINVAL;
 }
 
-- 
2.51.0