[PATCH v5 07/20] x86/resctrl: Introduce the interface to display monitor mode

[Babu Moger <babu.moger@amd.com>]

The ABMC feature provides an option to the user to assign a hardware
counter to an RMID and monitor the bandwidth as long as it is assigned.
ABMC mode is enabled by default when supported. System can be one mode
at a time (Legacy monitor mode or ABMC mode).

Provide an interface to display the monitor mode on the system.
    $cat /sys/fs/resctrl/info/L3_MON/mbm_mode
    [abmc]
    legacy

Signed-off-by: Babu Moger <babu.moger@amd.com>
---
v5: Changed interface name to mbm_mode.
    It will be always available even if ABMC feature is not supported.
    Added description in resctrl.rst about ABMC mode.
    Fixed display abmc and legacy consistantly.

v4: Fixed the checks for legacy and abmc mode. Default it ABMC.

v3: New patch to display ABMC capability.
---
 Documentation/arch/x86/resctrl.rst     | 30 ++++++++++++++++++++++++++
 arch/x86/kernel/cpu/resctrl/monitor.c  |  2 ++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 26 ++++++++++++++++++++++
 3 files changed, 58 insertions(+)

diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index 30586728a4cd..108e494fd7cc 100644
--- a/Documentation/arch/x86/resctrl.rst
+++ b/Documentation/arch/x86/resctrl.rst
@@ -257,6 +257,36 @@ with the following files:
 	    # cat /sys/fs/resctrl/info/L3_MON/mbm_local_bytes_config
 	    0=0x30;1=0x30;3=0x15;4=0x15
 
+"mbm_mode":
+	Reports the list of assignable monitoring features supported. The
+	enclosed brackets indicate which feature is enabled.
+	::
+
+	  cat /sys/fs/resctrl/info/L3_MON/mbm_mode
+	  [abmc]
+	  legacy
+
+	The bandwidth monitoring feature on AMD system only guarantees that
+	RMIDs currently assigned to a processor will be tracked by hardware.
+	The counters of any other RMIDs which are no longer being tracked
+	will be reset to zero. The MBM event counters return "Unavailable"
+	for the RMIDs that are not tracked by hardware. So, there can be
+	only limited number of groups that can give guaranteed monitoring
+	numbers. With ever changing configurations there is no way to
+	definitely know which of these groups are being tracked for certain
+	point of time. Users do not have the option to monitor a group or
+	set of groups for certain period of time without worrying about
+	RMID being reset in between.
+
+	The ABMC feature provides an option to the user to assign a
+	hardware counter to an RMID and monitor the bandwidth as long as
+	it is assigned. The assigned RMID will be tracked by the hardware
+	until the user unassigns it manually. There is no need to worry
+	about counters being reset during this period.
+
+	Without ABMC enabled, monitoring will work in "legacy" mode
+	without assignment option.
+
 "max_threshold_occupancy":
 		Read/write file provides the largest value (in
 		bytes) at which a previously used LLC_occupancy
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 12793762ca24..6c4cb36b4b50 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -1245,6 +1245,8 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
 		}
 	}
 
+	resctrl_file_fflags_init("mbm_mode", RFTYPE_MON_INFO);
+
 	l3_mon_evt_init(r);
 
 	r->mon_capable = true;
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 471fc0dbd7c3..3988d7b86817 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -845,6 +845,26 @@ static int rdtgroup_rmid_show(struct kernfs_open_file *of,
 	return ret;
 }
 
+static int rdtgroup_mbm_mode_show(struct kernfs_open_file *of,
+				  struct seq_file *s, void *v)
+{
+	struct rdt_resource *r = of->kn->parent->priv;
+
+	if (r->mon.abmc_capable) {
+		if (resctrl_arch_get_abmc_enabled()) {
+			seq_puts(s, "[abmc]\n");
+			seq_puts(s, "legacy\n");
+		} else {
+			seq_puts(s, "abmc\n");
+			seq_puts(s, "[legacy]\n");
+		}
+	} else {
+		seq_puts(s, "[legacy]\n");
+	}
+
+	return 0;
+}
+
 #ifdef CONFIG_PROC_CPU_RESCTRL
 
 /*
@@ -1901,6 +1921,12 @@ static struct rftype res_common_files[] = {
 		.seq_show	= mbm_local_bytes_config_show,
 		.write		= mbm_local_bytes_config_write,
 	},
+	{
+		.name		= "mbm_mode",
+		.mode		= 0444,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= rdtgroup_mbm_mode_show,
+	},
 	{
 		.name		= "cpus",
 		.mode		= 0644,
-- 
2.34.1