[PATCH v2 5/6] x86,fs/resctrl: Add resctrl_arch_mbm_cntr_assign_fixed()

[Ben Horgan <ben.horgan@arm.com>]

Commit

  3b497c3f4f04 ("fs/resctrl: Introduce the interface to display monitoring modes")

introduced CONFIG_RESCTRL_ASSIGN_FIXED but left adding the Kconfig
entry until it was necessary. The counter assignment mode is fixed in
MPAM, even when there are assignable counters, and so addressing this
is needed to support MPAM.

To avoid the burden of another Kconfig entry, replace
CONFIG_RESCTRL_ASSIGN_FIXED with a new arch hook,
resctrl_arch_mbm_cntr_assign_fixed().

To enable better user reporting check use the new check in
resctrl_mbm_assign_mode_write().

Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
 arch/x86/kernel/cpu/resctrl/monitor.c |  5 +++++
 fs/resctrl/monitor.c                  |  8 +++++++-
 include/linux/resctrl.h               | 10 ++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 9bd87bae4983..aa7f8f1ecd22 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -523,6 +523,11 @@ bool resctrl_arch_mbm_cntr_assign_enabled(struct rdt_resource *r)
 	return resctrl_to_arch_res(r)->mbm_cntr_assign_enabled;
 }
 
+bool resctrl_arch_mbm_cntr_assign_fixed(struct rdt_resource *r)
+{
+	return false;
+}
+
 static void resctrl_abmc_config_one_amd(void *info)
 {
 	union l3_qos_abmc_cfg *abmc_cfg = info;
diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index a2da771d82df..62edb464410a 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -1455,7 +1455,7 @@ int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
 		else
 			seq_puts(s, "[default]\n");
 
-		if (!IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED)) {
+		if (!resctrl_arch_mbm_cntr_assign_fixed(r)) {
 			if (enabled)
 				seq_puts(s, "default\n");
 			else
@@ -1506,6 +1506,12 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
 	}
 
 	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
+		if (!resctrl_arch_mbm_cntr_assign_fixed(r)) {
+			ret = -EINVAL;
+			rdt_last_cmd_puts("Counter assignment mode is not configurable\n");
+			goto out_unlock;
+		}
+
 		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
 		if (ret)
 			goto out_unlock;
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 4ae63233b506..c85176999eb2 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -500,6 +500,16 @@ bool resctrl_arch_mbm_cntr_assign_enabled(struct rdt_resource *r);
  */
 int resctrl_arch_mbm_cntr_assign_set(struct rdt_resource *r, bool enable);
 
+/**
+ * resctrl_arch_mbm_cntr_assign_fixed() - Check if MBM counter assignment mode
+ *					  can be configured.
+ * @r:		Pointer to the resource structure.
+ *
+ * Return:
+ * true if the assignment mode is fixed, false otherwise.
+ */
+bool resctrl_arch_mbm_cntr_assign_fixed(struct rdt_resource *r);
+
 /*
  * Update the ctrl_val and apply this config right now.
  * Must be called on one of the domain's CPUs.
-- 
2.43.0