Introduce interface to switch between mbm_cntr_assign and default modes.

$ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
[mbm_cntr_assign]
default

To enable the "mbm_cntr_assign" mode:
$ echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode

To enable the default monitoring mode:
$ echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode

MBM event counters will reset when mbm_assign_mode is changed.

Signed-off-by: Babu Moger <babu.moger@amd.com>
---
v9: Fixed extra spaces in user documentation.
    Fixed problem changing the mode to mbm_cntr_assign mode when it is
    not supported. Added extra checks to detect if systems supports it.
    Used the rdtgroup_cntr_id_init to initialize cntr_id.

v8: Reset the internal counters after mbm_cntr_assign mode is changed.
    Renamed rdtgroup_mbm_cntr_reset() to mbm_cntr_reset()
    Updated the documentation to make text generic.

v7: Changed the interface name to mbm_assign_mode.
    Removed the references of ABMC.
    Added the changes to reset global and domain bitmaps.
    Added the changes to reset rmid.

v6: Changed the mode name to mbm_cntr_assign.
    Moved all the FS related code here.
    Added changes to reset mbm_cntr_map and resctrl group counters.

v5: Change log and mode description text correction.

v4: Minor commit text changes. Keep the default to ABMC when supported.
    Fixed comments to reflect changed interface "mbm_mode".

v3: New patch to address the review comments from upstream.
---
 Documentation/arch/x86/resctrl.rst     | 15 +++++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 81 +++++++++++++++++++++++++-
 2 files changed, 95 insertions(+), 1 deletion(-)

diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index 864fc004d646..1b39866e8b04 100644
--- a/Documentation/arch/x86/resctrl.rst
+++ b/Documentation/arch/x86/resctrl.rst
@@ -290,6 +290,21 @@ with the following files:
 	mbm_local_bytes may report 'Unavailable' if there is no counter associated
 	with that event.
 
+	* To enable "mbm_cntr_assign" mode:
+	  ::
+
+	    # echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
+
+	* To enable default monitoring mode:
+	  ::
+
+	    # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
+
+	The MBM events (mbm_total_bytes and/or mbm_local_bytes) associated with
+	counters may reset when mbm_assign_mode is changed. Moving to
+	mbm_cntr_assign mode require users to assign the counters to the events.
+	Otherwise, the MBM event counters will return "Unassigned" when read.
+
 "num_mbm_cntrs":
 	The number of monitoring counters available for assignment when the
 	architecture supports mbm_cntr_assign mode.
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index a8d21b0b2054..7fa6a86c6ca8 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -933,6 +933,84 @@ static void rdtgroup_cntr_id_init(struct rdtgroup *rdtgrp,
 	rdtgrp->mon.cntr_id[index] = MON_CNTR_UNSET;
 }
 
+static void mbm_cntr_reset(struct rdt_resource *r)
+{
+	struct rdtgroup *prgrp, *crgrp;
+	struct rdt_mon_domain *dom;
+
+	/*
+	 * Hardware counters will reset after switching the monitor mode.
+	 * Reset the architectural state so that reading of hardware
+	 * counter is not considered as an overflow in the next update.
+	 * Also reset the domain counter bitmap.
+	 */
+	list_for_each_entry(dom, &r->mon_domains, hdr.list) {
+		bitmap_zero(dom->mbm_cntr_map, r->mon.num_mbm_cntrs);
+		resctrl_arch_reset_rmid_all(r, dom);
+	}
+
+	/* Reset global MBM counter map */
+	bitmap_fill(r->mon.mbm_cntr_free_map, r->mon.num_mbm_cntrs);
+
+	/* Reset the cntr_id's for all the monitor groups */
+	list_for_each_entry(prgrp, &rdt_all_groups, rdtgroup_list) {
+		rdtgroup_cntr_id_init(prgrp, QOS_L3_MBM_TOTAL_EVENT_ID);
+		rdtgroup_cntr_id_init(prgrp, QOS_L3_MBM_LOCAL_EVENT_ID);
+		list_for_each_entry(crgrp, &prgrp->mon.crdtgrp_list,
+				    mon.crdtgrp_list) {
+			rdtgroup_cntr_id_init(crgrp, QOS_L3_MBM_TOTAL_EVENT_ID);
+			rdtgroup_cntr_id_init(crgrp, QOS_L3_MBM_LOCAL_EVENT_ID);
+		}
+	}
+}
+
+static ssize_t rdtgroup_mbm_assign_mode_write(struct kernfs_open_file *of,
+					      char *buf, size_t nbytes, loff_t off)
+{
+	struct rdt_resource *r = of->kn->parent->priv;
+	int ret = 0;
+	bool enable;
+
+	/* Valid input requires a trailing newline */
+	if (nbytes == 0 || buf[nbytes - 1] != '\n')
+		return -EINVAL;
+
+	buf[nbytes - 1] = '\0';
+
+	cpus_read_lock();
+	mutex_lock(&rdtgroup_mutex);
+
+	rdt_last_cmd_clear();
+
+	if (!strcmp(buf, "default")) {
+		enable = 0;
+	} else if (!strcmp(buf, "mbm_cntr_assign")) {
+		if (r->mon.mbm_cntr_assignable) {
+			enable = 1;
+		} else {
+			ret = -EINVAL;
+			rdt_last_cmd_puts("mbm_cntr_assign mode is not supported\n");
+			goto write_exit;
+		}
+	} else {
+		ret = -EINVAL;
+		rdt_last_cmd_puts("Unsupported assign mode\n");
+		goto write_exit;
+	}
+
+	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
+		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
+		if (!ret)
+			mbm_cntr_reset(r);
+	}
+
+write_exit:
+	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
+
+	return ret ?: nbytes;
+}
+
 #ifdef CONFIG_PROC_CPU_RESCTRL
 
 /*
@@ -2166,9 +2244,10 @@ static struct rftype res_common_files[] = {
 	},
 	{
 		.name		= "mbm_assign_mode",
-		.mode		= 0444,
+		.mode		= 0644,
 		.kf_ops		= &rdtgroup_kf_single_ops,
 		.seq_show	= rdtgroup_mbm_assign_mode_show,
+		.write		= rdtgroup_mbm_assign_mode_write,
 		.fflags		= RFTYPE_MON_INFO,
 	},
 	{
-- 
2.34.1