[PATCH v2 10/45] arm64: mpam: Add cpu_pm notifier to restore MPAM sysregs

Ben Horgan
2025-12-19T18:12:50Z

From: James Morse <james.morse@arm.com>

The MPAM system registers will be lost if the CPU is reset during PSCI's
CPU_SUSPEND.

Add a PM notifier to restore them.

mpam_thread_switch(current) can't be used as this won't make any changes if
the in-memory copy says the register already has the correct value. In
reality the system register is UNKNOWN out of reset.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
arch/arm64/kernel/mpam.c | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)

diff --git a/arch/arm64/kernel/mpam.c b/arch/arm64/kernel/mpam.c
index e6feff2324ac..dbe0a2d05abb 100644
--- a/arch/arm64/kernel/mpam.c
+++ b/arch/arm64/kernel/mpam.c
@@ -4,6 +4,7 @@
#include <asm/mpam.h>

#include <linux/arm_mpam.h>
+#include <linux/cpu_pm.h>
#include <linux/jump_label.h>
#include <linux/percpu.h>

@@ -13,12 +14,41 @@ DEFINE_PER_CPU(u64, arm64_mpam_current);

u64 arm64_mpam_global_default;

+static int mpam_pm_notifier(struct notifier_block *self,
+ unsigned long cmd, void *v)
+{
+ u64 regval;
+ int cpu = smp_processor_id();
+
+ switch (cmd) {
+ case CPU_PM_EXIT:
+ /*
+ * Don't use mpam_thread_switch() as the system register
+ * value has changed under our feet.
+ */
+ regval = READ_ONCE(per_cpu(arm64_mpam_current, cpu));
+ write_sysreg_s(regval, SYS_MPAM1_EL1);
+ isb();
+
+ write_sysreg_s(regval, SYS_MPAM0_EL1);
+
+ return NOTIFY_OK;
+ default:
+ return NOTIFY_DONE;
+ }
+}
+
+static struct notifier_block mpam_pm_nb = {
+ .notifier_call = mpam_pm_notifier,
+};
+
static int __init arm64_mpam_register_cpus(void)
{
u64 mpamidr = read_sanitised_ftr_reg(SYS_MPAMIDR_EL1);
u16 partid_max = FIELD_GET(MPAMIDR_EL1_PARTID_MAX, mpamidr);
u8 pmg_max = FIELD_GET(MPAMIDR_EL1_PMG_MAX, mpamidr);

+ cpu_pm_register_notifier(&mpam_pm_nb);
return mpam_register_requestor(partid_max, pmg_max);
}
/* Must occur before mpam_msc_driver_init() from subsys_initcall() */
--
2.43.0