x86/resctrl: Add write option to "mba_MBps_event" file

The "mba_MBps" mount option provides an alternate method to control memory
bandwidth. Instead of specifying allowable bandwidth as a percentage of
maximum possible, the user provides a MiB/s limit value.

There is a file in each CTRL_MON group directory that shows the event
currently in use.

Allow writing that file to choose a different event.

A user can choose any of the memory bandwidth monitoring events listed in
/sys/fs/resctrl/info/L3_mon/mon_features independently for each CTRL_MON group
by writing to each of the "mba_MBps_event" files.

Signed-off-by: Tony Luck <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Reviewed-by: Reinette Chatre <[email protected]>
Tested-by: Babu Moger <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: aegl

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

@@ -518,6 +518,46 @@ static int smp_mon_event_count(void *arg)
 	return 0;
 }
 
+ssize_t rdtgroup_mba_mbps_event_write(struct kernfs_open_file *of,
+				      char *buf, size_t nbytes, loff_t off)
+{
+	struct rdtgroup *rdtgrp;
+	int ret = 0;
+
+	/* Valid input requires a trailing newline */
+	if (nbytes == 0 || buf[nbytes - 1] != '\n')
+		return -EINVAL;
+	buf[nbytes - 1] = '\0';
+
+	rdtgrp = rdtgroup_kn_lock_live(of->kn);
+	if (!rdtgrp) {
+		rdtgroup_kn_unlock(of->kn);
+		return -ENOENT;
+	}
+	rdt_last_cmd_clear();
+
+	if (!strcmp(buf, "mbm_local_bytes")) {
+		if (is_mbm_local_enabled())
+			rdtgrp->mba_mbps_event = QOS_L3_MBM_LOCAL_EVENT_ID;
+		else
+			ret = -EINVAL;
+	} else if (!strcmp(buf, "mbm_total_bytes")) {
+		if (is_mbm_total_enabled())
+			rdtgrp->mba_mbps_event = QOS_L3_MBM_TOTAL_EVENT_ID;
+		else
+			ret = -EINVAL;
+	} else {
+		ret = -EINVAL;
+	}
+
+	if (ret)
+		rdt_last_cmd_printf("Unsupported event id '%s'\n", buf);
+
+	rdtgroup_kn_unlock(of->kn);
+
+	return ret ?: nbytes;
+}
+
 int rdtgroup_mba_mbps_event_show(struct kernfs_open_file *of,
 				 struct seq_file *s, void *v)
 {

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

@@ -610,6 +610,8 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
 				char *buf, size_t nbytes, loff_t off);
 int rdtgroup_schemata_show(struct kernfs_open_file *of,
 			   struct seq_file *s, void *v);
+ssize_t rdtgroup_mba_mbps_event_write(struct kernfs_open_file *of,
+				      char *buf, size_t nbytes, loff_t off);
 int rdtgroup_mba_mbps_event_show(struct kernfs_open_file *of,
 				 struct seq_file *s, void *v);
 bool rdtgroup_cbm_overlaps(struct resctrl_schema *s, struct rdt_ctrl_domain *d,

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

@@ -1952,8 +1952,9 @@ static struct rftype res_common_files[] = {
 	},
 	{
 		.name		= "mba_MBps_event",
-		.mode		= 0444,
+		.mode		= 0644,
 		.kf_ops		= &rdtgroup_kf_single_ops,
+		.write		= rdtgroup_mba_mbps_event_write,
 		.seq_show	= rdtgroup_mba_mbps_event_show,
 	},
 	{