[PATCH v1 18/31] x86/resctrl: Allow resctrl_arch_mon_event_config_write() to return an error

[James Morse <james.morse@arm.com>]

resctrl_arch_mon_event_config_write() writes a bitmap of events provided
by user-space into the configuration register for the monitors.

This assumes that all architectures support all the features each bit
corresponds to.

MPAM can filter monitors based on read, write, or both, but there are
many more options in the existing bitmap. To allow this interface to
work for machines with MPAM, allow the architecture helper to return
an error if an incompatible bitmap is set.

When valid values are provided, there is no change in behaviour. If
an invalid value is provided, currently it is silently ignored, but
last_cmd_status is updated. After this change, the parser will stop
at the first invalid value and return an error to user-space. This
matches the way changes to the schemata file are made.

Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 20 ++++++++++++++++----
 include/linux/resctrl.h                |  1 +
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 3d3a839eba6b..56a0bfdc11f7 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -1685,13 +1685,16 @@ void resctrl_arch_mon_event_config_write(void *info)
 	index = mon_event_config_index_get(mon_info->evtid);
 	if (index == INVALID_CONFIG_INDEX) {
 		pr_warn_once("Invalid event id %d\n", mon_info->evtid);
+		mon_info->err = -EINVAL;
 		return;
 	}
 	wrmsr(MSR_IA32_EVT_CFG_BASE + index, mon_info->mon_config, 0);
+
+	mon_info->err = 0;
 }
 
-static void mbm_config_write_domain(struct rdt_resource *r,
-				    struct rdt_domain *d, u32 evtid, u32 val)
+static int mbm_config_write_domain(struct rdt_resource *r,
+				   struct rdt_domain *d, u32 evtid, u32 val)
 {
 	struct resctrl_mon_config_info mon_info = {0};
 
@@ -1704,7 +1707,7 @@ static void mbm_config_write_domain(struct rdt_resource *r,
 	mon_info.evtid = evtid;
 	mondata_config_read(&mon_info);
 	if (mon_info.mon_config == val)
-		return;
+		return 0;
 
 	mon_info.mon_config = val;
 
@@ -1716,6 +1719,10 @@ static void mbm_config_write_domain(struct rdt_resource *r,
 	 */
 	smp_call_function_any(&d->cpu_mask, resctrl_arch_mon_event_config_write,
 			      &mon_info, 1);
+	if (mon_info.err) {
+		rdt_last_cmd_puts("Invalid event configuration\n");
+		return mon_info.err;
+	}
 
 	/*
 	 * When an Event Configuration is changed, the bandwidth counters
@@ -1727,6 +1734,8 @@ static void mbm_config_write_domain(struct rdt_resource *r,
 	 * mbm_local and mbm_total counts for all the RMIDs.
 	 */
 	resctrl_arch_reset_rmid_all(r, d);
+
+	return 0;
 }
 
 static int mon_config_write(struct rdt_resource *r, char *tok, u32 evtid)
@@ -1734,6 +1743,7 @@ static int mon_config_write(struct rdt_resource *r, char *tok, u32 evtid)
 	char *dom_str = NULL, *id_str;
 	unsigned long dom_id, val;
 	struct rdt_domain *d;
+	int err;
 
 	/* Walking r->domains, ensure it can't race with cpuhp */
 	lockdep_assert_cpus_held();
@@ -1765,7 +1775,9 @@ static int mon_config_write(struct rdt_resource *r, char *tok, u32 evtid)
 
 	list_for_each_entry(d, &r->domains, list) {
 		if (d->id == dom_id) {
-			mbm_config_write_domain(r, d, evtid, val);
+			err = mbm_config_write_domain(r, d, evtid, val);
+			if (err)
+				return err;
 			goto next;
 		}
 	}
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 8a7367d1ce45..6705d7960dfd 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -200,6 +200,7 @@ struct resctrl_mon_config_info {
 	struct rdt_domain   *d;
 	u32                  evtid;
 	u32                  mon_config;
+	int                  err;
 };
 
 /*
-- 
2.39.2