x86/resctrl: Remove data_width and the tabular format

The resctrl architecture code provides a data_width for the controls of each
resource. This is used to zero pad all control values in the schemata file so
they appear in columns. The same is done with the resource names to complete
the visual effect. e.g.

  | SMBA:0=2048
  |   L3:0=00ff

AMD platforms discover their maximum bandwidth for the MB resource from
firmware, but hard-code the data_width to 4. If the maximum bandwidth requires
more digits - the tabular format is silently broken.  This is also broken when
the mba_MBps mount option is used as the field width isn't updated. If new
schema are added resctrl will need to be able to determine the maximum width.
The benefit of this pretty-printing is questionable.

Instead of handling runtime discovery of the data_width for AMD platforms,
remove the feature. These fields are always zero padded so should be harmless
to remove if the whole field has been treated as a number.  In the above
example, this would now look like this:

  | SMBA:0=2048
  |   L3:0=ff

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
Reviewed-by: Babu Moger <babu.moger@amd.com>
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Tested-by: Amit Singh Tomar <amitsinght@marvell.com> # arm64
Tested-by: Shanker Donthineni <sdonthineni@nvidia.com> # arm64
Tested-by: Babu Moger <babu.moger@amd.com>
Link: https://lore.kernel.org/r/20250311183715.16445-7-james.morse@arm.com

Author: James Morse

arch/x86/kernel/cpu/resctrl/core.c

@@ -43,12 +43,6 @@ static DEFINE_MUTEX(domain_list_lock);
  */
 DEFINE_PER_CPU(struct resctrl_pqr_state, pqr_state);
 
-/*
- * Used to store the max resource name width and max resource data width
- * to display the schemata in a tabular format
- */
-int max_name_width, max_data_width;
-
 /*
  * Global boolean for rdt_alloc which is true if any
  * resource allocation is enabled.
@@ -228,7 +222,6 @@ static __init bool __get_mem_config_intel(struct rdt_resource *r)
 			return false;
 		r->membw.arch_needs_linear = false;
 	}
-	r->data_width = 3;
 
 	if (boot_cpu_has(X86_FEATURE_PER_THREAD_MBA))
 		r->membw.throttle_mode = THREAD_THROTTLE_PER_THREAD;
@@ -269,8 +262,6 @@ static __init bool __rdt_get_mem_config_amd(struct rdt_resource *r)
 	r->membw.throttle_mode = THREAD_THROTTLE_UNDEFINED;
 	r->membw.min_bw = 0;
 	r->membw.bw_gran = 1;
-	/* Max value is 2048, Data width should be 4 in decimal */
-	r->data_width = 4;
 
 	r->alloc_capable = true;
 
@@ -290,7 +281,6 @@ static void rdt_get_cache_alloc_cfg(int idx, struct rdt_resource *r)
 	r->cache.cbm_len = eax.split.cbm_len + 1;
 	r->default_ctrl = BIT_MASK(eax.split.cbm_len + 1) - 1;
 	r->cache.shareable_bits = ebx & r->default_ctrl;
-	r->data_width = (r->cache.cbm_len + 3) / 4;
 	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
 		r->cache.arch_has_sparse_bitmasks = ecx.split.noncont;
 	r->alloc_capable = true;
@@ -786,20 +776,6 @@ static int resctrl_arch_offline_cpu(unsigned int cpu)
 	return 0;
 }
 
-/*
- * Choose a width for the resource name and resource data based on the
- * resource that has widest name and cbm.
- */
-static __init void rdt_init_padding(void)
-{
-	struct rdt_resource *r;
-
-	for_each_alloc_capable_rdt_resource(r) {
-		if (r->data_width > max_data_width)
-			max_data_width = r->data_width;
-	}
-}
-
 enum {
 	RDT_FLAG_CMT,
 	RDT_FLAG_MBM_TOTAL,
@@ -1102,8 +1078,6 @@ static int __init resctrl_late_init(void)
 	if (!get_rdt_resources())
 		return -ENODEV;
 
-	rdt_init_padding();
-
 	state = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
 				  "x86/resctrl/cat:online:",
 				  resctrl_arch_online_cpu,

arch/x86/kernel/cpu/resctrl/ctrlmondata.c

@@ -487,8 +487,7 @@ static void show_doms(struct seq_file *s, struct resctrl_schema *schema, int clo
 			ctrl_val = resctrl_arch_get_config(r, dom, closid,
 							   schema->conf_type);
 
-		seq_printf(s, schema->fmt_str, dom->hdr.id, max_data_width,
-			   ctrl_val);
+		seq_printf(s, schema->fmt_str, dom->hdr.id, ctrl_val);
 		sep = true;
 	}
 	seq_puts(s, "\n");

arch/x86/kernel/cpu/resctrl/internal.h

@@ -326,7 +326,7 @@ struct rdtgroup {
 /* List of all resource groups */
 extern struct list_head rdt_all_groups;
 
-extern int max_name_width, max_data_width;
+extern int max_name_width;
 
 int __init rdtgroup_init(void);
 void __exit rdtgroup_exit(void);

arch/x86/kernel/cpu/resctrl/rdtgroup.c

@@ -57,6 +57,12 @@ static struct kernfs_node *kn_mongrp;
 /* Kernel fs node for "mon_data" directory under root */
 static struct kernfs_node *kn_mondata;
 
+/*
+ * Used to store the max resource name width to display the schemata names in
+ * a tabular format.
+ */
+int max_name_width;
+
 static struct seq_buf last_cmd_status;
 static char last_cmd_status_buf[512];
 
@@ -2613,10 +2619,10 @@ static int schemata_list_add(struct rdt_resource *r, enum resctrl_conf_type type
 
 	switch (r->schema_fmt) {
 	case RESCTRL_SCHEMA_BITMAP:
-		s->fmt_str = "%d=%0*x";
+		s->fmt_str = "%d=%x";
 		break;
 	case RESCTRL_SCHEMA_RANGE:
-		s->fmt_str = "%d=%0*u";
+		s->fmt_str = "%d=%u";
 		break;
 	}
 

include/linux/resctrl.h

@@ -214,7 +214,6 @@ enum resctrl_schema_fmt {
  * @ctrl_domains:	RCU list of all control domains for this resource
  * @mon_domains:	RCU list of all monitor domains for this resource
  * @name:		Name to use in "schemata" file.
- * @data_width:		Character width of data when displaying
  * @default_ctrl:	Specifies default cache cbm or memory B/W percent.
  * @schema_fmt:		Which format string and parser is used for this schema.
  * @evt_list:		List of monitoring events
@@ -232,7 +231,6 @@ struct rdt_resource {
 	struct list_head	ctrl_domains;
 	struct list_head	mon_domains;
 	char			*name;
-	int			data_width;
 	u32			default_ctrl;
 	enum resctrl_schema_fmt	schema_fmt;
 	struct list_head	evt_list;