[RFC PATCH v3 15/17] x86/resctrl: Introduce the interface switch between ABMC and legacy_mbm

[Babu Moger]

Introduce rdtgroup_mbm_assign_write to switch between ABMC and legacy_mbm.

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.

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>

---
v3: New patch to address the review comments from upstream.
---
 Documentation/arch/x86/resctrl.rst     | 14 ++++++++-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 39 +++++++++++++++++++++++++-
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index e06ffddb64f6..3e441b828765 100644
--- a/Documentation/arch/x86/resctrl.rst
+++ b/Documentation/arch/x86/resctrl.rst
@@ -260,7 +260,19 @@ with the following files:
 "mbm_assign":
 	Available when assignable monitoring features are supported.
 	Reports the list of assignable features supported and the enclosed brackets
-	indicate the feature is enabled.
+	indicate the feature is enabled. Users will have the option to switch
+	between the monitoring features.
+	Examples:
+
+	* To enable ABMC feature:
+	  ::
+
+	   # echo  "abmc" > /sys/fs/resctrl/info/L3_MON/mbm_assign
+
+	* To enable the legacy monitoring feature:
+	  ::
+
+	   # echo  "legacy_mbm" > /sys/fs/resctrl/info/L3_MON/mbm_assign
 
 "mbm_assign_cntrs":
 	The number of assignable counters available when the assignable monitoring
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 2e58024e95e2..a6e0ef2631ae 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -896,6 +896,42 @@ 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;
+
+	if (!r->mbm_assign_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, "legacy_mbm"))
+		ret = resctrl_arch_set_abmc_enabled(RDT_RESOURCE_L3, false);
+	else if (!strcmp(buf, "abmc"))
+		ret = resctrl_arch_set_abmc_enabled(RDT_RESOURCE_L3, true);
+	else
+		ret = -EINVAL;
+
+	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
+
+	return ret ?: nbytes;
+}
+
 static int rdtgroup_mbm_assign_cntrs_show(struct kernfs_open_file *of,
 					  struct seq_file *s, void *v)
 {
@@ -2078,9 +2114,10 @@ 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		= "mbm_assign_cntrs",
-- 
2.34.1