Message-ID: <20251126171653.1004321-4-atomlin@atomlin.com>
Date: Wed, 26 Nov 2025 12:16:52 -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,
	atomlin@...mlin.com,
	sean@...e.io,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] x86/resctrl: Add "*" shorthand to set minimum io_alloc CBM for all domains

This patch introduces a special domain ID selector "*" for io_alloc_cbm
that allows setting the CBM of each cache domain to its minimum number
of consecutive bits in a single operation. For example, writing "*=0" to
/sys/fs/resctrl/info/L3/io_alloc_cbm programs each domain's CBM to the
hardware-defined minimum, greatly simplifying automation and management
tasks. The user is required to specify the correct minimum stored in
/sys/fs/resctrl/info/L3/min_cbm_bits.

Signed-off-by: Aaron Tomlin <atomlin@...mlin.com>
---
 Documentation/filesystems/resctrl.rst     |  10 ++
 arch/x86/kernel/cpu/resctrl/core.c        |   2 +-
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c |  23 +++--
 fs/resctrl/ctrlmondata.c                  | 108 +++++++++++++++++-----
 fs/resctrl/internal.h                     |  13 +++
 fs/resctrl/rdtgroup.c                     |   2 +-
 include/linux/resctrl.h                   |  30 +++++-
 7 files changed, 155 insertions(+), 33 deletions(-)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index 8c8ce678148a..9c128c8fba86 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -215,6 +215,16 @@ related to allocation:
 			# cat /sys/fs/resctrl/info/L3/io_alloc_cbm
 			0=00ff;1=000f
 
+		Set each CBM to their minimum number of consecutive bits.
+
+		A special value "*" is required to represent all cache IDs.
+		The user should specify the correct minimum stored in
+		/sys/fs/resctrl/info/L3/min_cbm_bits.
+
+		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/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 3792ab4819dc..44aea6b534e0 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -276,7 +276,7 @@ static void rdt_get_cdp_config(int level)
 
 static void rdt_set_io_alloc_capable(struct rdt_resource *r)
 {
-	r->cache.io_alloc_capable = true;
+	r->cache.io_alloc.io_alloc_capable = true;
 }
 
 static void rdt_get_cdp_l3_config(void)
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index b20e705606b8..0f051d848422 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -57,14 +57,19 @@ int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid)
 		hw_dom = resctrl_to_arch_ctrl_dom(d);
 		msr_param.res = NULL;
 		for (t = 0; t < CDP_NUM_TYPES; t++) {
-			cfg = &hw_dom->d_resctrl.staged_config[t];
-			if (!cfg->have_new_ctrl)
-				continue;
-
-			idx = resctrl_get_config_index(closid, t);
-			if (cfg->new_ctrl == hw_dom->ctrl_val[idx])
-				continue;
-			hw_dom->ctrl_val[idx] = cfg->new_ctrl;
+			if (resctrl_should_io_alloc_min_cbm(r)) {
+				idx = resctrl_get_config_index(closid, t);
+				hw_dom->ctrl_val[idx] = apply_io_alloc_min_cbm(r);
+			} else {
+				cfg = &hw_dom->d_resctrl.staged_config[t];
+				if (!cfg->have_new_ctrl)
+					continue;
+
+				idx = resctrl_get_config_index(closid, t);
+				if (cfg->new_ctrl == hw_dom->ctrl_val[idx])
+					continue;
+				hw_dom->ctrl_val[idx] = cfg->new_ctrl;
+			}
 
 			if (!msr_param.res) {
 				msr_param.low = idx;
@@ -123,7 +128,7 @@ int resctrl_arch_io_alloc_enable(struct rdt_resource *r, bool enable)
 {
 	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
 
-	if (hw_res->r_resctrl.cache.io_alloc_capable &&
+	if (hw_res->r_resctrl.cache.io_alloc.io_alloc_capable &&
 	    hw_res->sdciae_enabled != enable) {
 		_resctrl_sdciae_enable(r, enable);
 		hw_res->sdciae_enabled = enable;
diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
index 5f6f96d70e4a..b3abd781899f 100644
--- a/fs/resctrl/ctrlmondata.c
+++ b/fs/resctrl/ctrlmondata.c
@@ -688,7 +688,7 @@ int resctrl_io_alloc_show(struct kernfs_open_file *of, struct seq_file *seq, voi
 
 	mutex_lock(&rdtgroup_mutex);
 
-	if (r->cache.io_alloc_capable) {
+	if (r->cache.io_alloc.io_alloc_capable) {
 		if (resctrl_arch_get_io_alloc_enabled(r))
 			seq_puts(seq, "enabled\n");
 		else
@@ -712,13 +712,31 @@ static bool resctrl_io_alloc_closid_supported(u32 io_alloc_closid)
 	return io_alloc_closid < closids_supported();
 }
 
+/**
+ * resctrl_sync_cdp_peer - Mirror staged configuration to the CDP peer type
+ *
+ * @s: resctrl schema
+ * @d: resctrl control domain
+ *
+ * The caller must ensure CDP is enabled for the resource and must be
+ * called under the cpu hotplug lock and rdtgroup mutex
+ */
+static void resctrl_sync_cdp_peer(struct resctrl_schema *s, struct rdt_ctrl_domain *d)
+{
+	enum resctrl_conf_type peer_type;
+
+	peer_type = resctrl_peer_type(s->conf_type);
+	memcpy(&d->staged_config[peer_type],
+	       &d->staged_config[s->conf_type],
+	       sizeof(d->staged_config[0]));
+}
+
 /*
  * Initialize io_alloc CLOSID cache resource CBM with all usable (shared
  * and unused) cache portions.
  */
 static int resctrl_io_alloc_init_cbm(struct resctrl_schema *s, u32 closid)
 {
-	enum resctrl_conf_type peer_type;
 	struct rdt_resource *r = s->res;
 	struct rdt_ctrl_domain *d;
 	int ret;
@@ -731,11 +749,8 @@ static int resctrl_io_alloc_init_cbm(struct resctrl_schema *s, u32 closid)
 
 	/* Keep CDP_CODE and CDP_DATA of io_alloc CLOSID's CBM in sync. */
 	if (resctrl_arch_get_cdp_enabled(r->rid)) {
-		peer_type = resctrl_peer_type(s->conf_type);
 		list_for_each_entry(d, &s->res->ctrl_domains, hdr.list)
-			memcpy(&d->staged_config[peer_type],
-			       &d->staged_config[s->conf_type],
-			       sizeof(d->staged_config[0]));
+			resctrl_sync_cdp_peer(s, d);
 	}
 
 	ret = resctrl_arch_update_domains(r, closid);
@@ -903,29 +918,82 @@ int resctrl_io_alloc_cbm_show(struct kernfs_open_file *of, struct seq_file *seq,
 	return ret;
 }
 
+/**
+ * parse_domain_cbm - Parse "domain=cbm" and return either side
+ *
+ * @line_ptr: Pointer to the input string
+ * @out_val: Output from parsed value (either domain ID or CDM)
+ * @which: Selector for which side to parse
+ *
+ * It is assumed that *line_ptr and *out_val are valid.
+ *
+ * Return: 0 on success and advance *line_ptr to point past the
+ * delimiter, EINVAL on parsing error
+ */
+static int parse_domain_cbm(char **line_ptr, unsigned long *out_val,
+			    enum resctrl_kv_sel which)
+{
+	char *rhs, *lhs, *tok;
+	unsigned int base;
+
+	rhs = *line_ptr;
+
+	lhs = strsep(&rhs, "=");
+	if (!lhs || !rhs)
+		goto err;
+
+	if (which == RDT_PARSE_DOMAIN) {
+		tok = lhs;
+		base = 10;
+	} else {
+		tok = rhs;
+		base = 16;
+	}
+	tok = strim(tok);
+
+	if (kstrtoul(tok, base, out_val))
+		goto err;
+
+	*line_ptr = rhs;
+	return 0;
+err:
+	rdt_last_cmd_puts("Invalid domain=cbm: missing '=' or non-numeric value\n");
+	return -EINVAL;
+}
+
 static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
 				       struct resctrl_schema *s, u32 closid)
 {
-	enum resctrl_conf_type peer_type;
 	struct rdt_parse_data data;
 	struct rdt_ctrl_domain *d;
-	char *dom = NULL, *id;
-	unsigned long dom_id;
+	char *dom = NULL;
+	unsigned long out_val;
+	int ret;
+
+	if (line[0] == '*') {
+		ret = parse_domain_cbm(&line, &out_val, RDT_PARSE_CBM);
+		if (ret)
+			return ret;
 
+		if (out_val == r->cache.min_cbm_bits) {
+			r->cache.io_alloc.io_alloc_min_cbm = true;
+			return 0;
+		}
+		rdt_last_cmd_puts("Invalid io_alloc min CBM\n");
+		return -EINVAL;
+	}
 next:
 	if (!line || line[0] == '\0')
 		return 0;
 
 	dom = strsep(&line, ";");
-	id = strsep(&dom, "=");
-	if (!dom || kstrtoul(id, 10, &dom_id)) {
-		rdt_last_cmd_puts("Missing '=' or non-numeric domain\n");
-		return -EINVAL;
-	}
+	ret = parse_domain_cbm(&line, &out_val, RDT_PARSE_DOMAIN);
+	if (ret)
+		return ret;
 
 	dom = strim(dom);
 	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
-		if (d->hdr.id == dom_id) {
+		if (d->hdr.id == out_val) {
 			data.buf = dom;
 			data.mode = RDT_MODE_SHAREABLE;
 			data.closid = closid;
@@ -935,12 +1003,8 @@ static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
 			 * Keep io_alloc CLOSID's CBM of CDP_CODE and CDP_DATA
 			 * in sync.
 			 */
-			if (resctrl_arch_get_cdp_enabled(r->rid)) {
-				peer_type = resctrl_peer_type(s->conf_type);
-				memcpy(&d->staged_config[peer_type],
-				       &d->staged_config[s->conf_type],
-				       sizeof(d->staged_config[0]));
-			}
+			if (resctrl_arch_get_cdp_enabled(r->rid))
+				resctrl_sync_cdp_peer(s, d);
 			goto next;
 		}
 	}
@@ -982,6 +1046,8 @@ ssize_t resctrl_io_alloc_cbm_write(struct kernfs_open_file *of, char *buf,
 		goto out_clear_configs;
 
 	ret = resctrl_arch_update_domains(r, io_alloc_closid);
+	if (resctrl_should_io_alloc_min_cbm(r))
+		r->cache.io_alloc.io_alloc_min_cbm = false;
 
 out_clear_configs:
 	rdt_staged_configs_clear();
diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index bff4a54ae333..3846737992bb 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -143,6 +143,19 @@ enum rdt_group_type {
 	RDT_NUM_GROUP,
 };
 
+/**
+ * enum resctrl_kv_sel - Selector for "domain=cbm" key/value parsing
+ * @RDT_PARSE_DOMAIN: Parse the left-hand side (domain ID)
+ * @RDT_PARSE_CBM: Parse the right-hand side (CBM value)
+ *
+ * Used by parsers of key/value pairs formatted as "domain=cbm" to indicate
+ * which token should be extracted and converted.
+ */
+enum resctrl_kv_sel {
+	RDT_PARSE_DOMAIN,
+	RDT_PARSE_CBM,
+};
+
 /**
  * enum rdtgrp_mode - Mode of a RDT resource group
  * @RDT_MODE_SHAREABLE: This resource group allows sharing of its allocations
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index e1dc63b2218f..83ce3bafa5cb 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -2196,7 +2196,7 @@ static void io_alloc_init(void)
 {
 	struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
 
-	if (r->cache.io_alloc_capable) {
+	if (r->cache.io_alloc.io_alloc_capable) {
 		resctrl_file_fflags_init("io_alloc", RFTYPE_CTRL_INFO |
 					 RFTYPE_RES_CACHE);
 		resctrl_file_fflags_init("io_alloc_cbm",
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 54701668b3df..9e75959565dc 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -215,7 +215,10 @@ struct resctrl_cache {
 	unsigned int	shareable_bits;
 	bool		arch_has_sparse_bitmasks;
 	bool		arch_has_per_cpu_cfg;
-	bool		io_alloc_capable;
+	struct {
+		bool io_alloc_capable;
+		bool io_alloc_min_cbm;
+	} io_alloc;
 };
 
 /**
@@ -415,6 +418,31 @@ static inline bool resctrl_is_mbm_event(enum resctrl_event_id eventid)
 		eventid <= QOS_L3_MBM_LOCAL_EVENT_ID);
 }
 
+/**
+ * apply_io_alloc_min_cbm() - Apply minimum io_alloc CBM
+ *
+ * @r: resctrl resource
+ *
+ * Return: Minimum number of consecutive io_alloc CBM bits to be set.
+ */
+static inline u32 apply_io_alloc_min_cbm(struct rdt_resource *r)
+{
+	return r->cache.min_cbm_bits;
+}
+
+/**
+ * resctrl_should_io_alloc_min_cbm() - Should the minimum io_alloc
+ *				       CBM be applied
+ * @r: resctrl resource
+ *
+ * Return: True if the minimum number of consecutive
+ * bits to be set in the io_alloc CBM should be applied.
+ */
+static inline bool resctrl_should_io_alloc_min_cbm(struct rdt_resource *r)
+{
+	return r->cache.io_alloc.io_alloc_min_cbm;
+}
+
 u32 resctrl_get_mon_evt_cfg(enum resctrl_event_id eventid);
 
 /* Iterate over all memory bandwidth events */
-- 
2.51.0

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