[PATCH v4 17/19] x86/resctrl: Introduce the interface switch between ABMC and mbm_legacy

[Babu Moger]

Introduce interface to switch between ABMC and legacy_mbm modes.

By default ABMC is enabled on resctrl mount if the feature is available.
However, user will have the option to go back to legacy_mbm if required.

$ cat /sys/fs/resctrl/info/L3_MON/mbm_assign
[abmc]
mbm_legacy

To enable the legacy monitoring feature:
$ echo  "mbm_legacy" > /sys/fs/resctrl/info/L3_MON/mbm_assign

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
v4: Minor commit text changes. Keep the default to ABMC when supported.

v3: New patch to address the review comments from upstream.
---
 Documentation/arch/x86/resctrl.rst     | 10 +++++++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 40 +++++++++++++++++++++++++-
 2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index ab3cde61a124..fd050d4d22cd 100644
--- a/Documentation/arch/x86/resctrl.rst
+++ b/Documentation/arch/x86/resctrl.rst
@@ -271,6 +271,16 @@ with the following files:
 	  [abmc]
 	  mbm_legacy
 
+	* To enable ABMC feature:
+	  ::
+
+	    # echo  "abmc" > /sys/fs/resctrl/info/L3_MON/mbm_assign
+
+	* To enable the legacy monitoring feature:
+	  ::
+
+	    # echo  "mbm_legacy" > /sys/fs/resctrl/info/L3_MON/mbm_assign
+
 "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/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index f452b6d9bb99..d77ff059269a 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -908,6 +908,43 @@ static int rdtgroup_mbm_assign_show(struct kernfs_open_file *of,
 	return 0;
 }
 
+/*
+ * rdtgroup_mode_write - Modify the resource group's mode
+ */
+static ssize_t rdtgroup_mbm_assign_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;
+
+	if (!r->abmc_capable)
+		return -EINVAL;
+
+	/* 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, "mbm_legacy"))
+		resctrl_abmc_disable(RDT_RESOURCE_L3);
+	else if (!strcmp(buf, "abmc"))
+		ret = resctrl_abmc_enable(RDT_RESOURCE_L3);
+	else
+		ret = -EINVAL;
+
+	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
+
+	return ret ?: nbytes;
+}
+
 #ifdef CONFIG_PROC_CPU_RESCTRL
 
 /*
@@ -2087,9 +2124,10 @@ static struct rftype res_common_files[] = {
 	},
 	{
 		.name		= "mbm_assign",
-		.mode		= 0444,
+		.mode		= 0644,
 		.kf_ops		= &rdtgroup_kf_single_ops,
 		.seq_show	= rdtgroup_mbm_assign_show,
+		.write		= rdtgroup_mbm_assign_write,
 	},
 	{
 		.name		= "cpus",
-- 
2.34.1