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

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Message-ID: <20251219181147.3404071-11-ben.horgan@arm.com>
Date: Fri, 19 Dec 2025 18:11:12 +0000
From: Ben Horgan <ben.horgan@....com>
To: ben.horgan@....com
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Subject: [PATCH v2 10/45] arm64: mpam: Add cpu_pm notifier to restore MPAM sysregs

From: James Morse <james.morse@....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@....com>
Signed-off-by: Ben Horgan <ben.horgan@....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