arm64: smp: disable hotplug on trusted OS resident CPU

The trusted OS may reject CPU_OFF calls to its resident CPU, so we must
avoid issuing those. We never migrate a Trusted OS and we already take
care to prevent CPU_OFF PSCI call. However, this is not reflected
explicitly to the userspace. Any user can attempt to hotplug trusted OS
resident CPU. The entire motion of going through the various state
transitions in the CPU hotplug state machine gets executed and the
PSCI layer finally refuses to make CPU_OFF call.

This results is unnecessary unwinding of CPU hotplug state machine in
the kernel. Instead we can mark the trusted OS resident CPU as not
available for hotplug, so that the user attempt or request to do the
same will get immediately rejected.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

2 files changed, 16 insertions, 1 deletions

diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
index a543ab7e007c..c9f72b2665f1 100644
--- a/arch/arm64/kernel/psci.c
+++ b/arch/arm64/kernel/psci.c
@@ -46,6 +46,11 @@ static int cpu_psci_cpu_boot(unsigned int cpu)
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
+static bool cpu_psci_cpu_can_disable(unsigned int cpu)
+{
+	return !psci_tos_resident_on(cpu);
+}
+
 static int cpu_psci_cpu_disable(unsigned int cpu)
 {
 	/* Fail early if we don't have CPU_OFF support */
@@ -109,6 +114,7 @@ const struct cpu_operations cpu_psci_ops = {
 	.cpu_prepare	= cpu_psci_cpu_prepare,
 	.cpu_boot	= cpu_psci_cpu_boot,
 #ifdef CONFIG_HOTPLUG_CPU
+	.cpu_can_disable = cpu_psci_cpu_can_disable,
 	.cpu_disable	= cpu_psci_cpu_disable,
 	.cpu_die	= cpu_psci_cpu_die,
 	.cpu_kill	= cpu_psci_cpu_kill,
diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 9c4bad7d7131..57ff38600828 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -357,6 +357,15 @@ void __init setup_arch(char **cmdline_p)
 	}
 }
 
+static inline bool cpu_can_disable(unsigned int cpu)
+{
+#ifdef CONFIG_HOTPLUG_CPU
+	if (cpu_ops[cpu] && cpu_ops[cpu]->cpu_can_disable)
+		return cpu_ops[cpu]->cpu_can_disable(cpu);
+#endif
+	return false;
+}
+
 static int __init topology_init(void)
 {
 	int i;
@@ -366,7 +375,7 @@ static int __init topology_init(void)
 
 	for_each_possible_cpu(i) {
 		struct cpu *cpu = &per_cpu(cpu_data.cpu, i);
-		cpu->hotpluggable = 1;
+		cpu->hotpluggable = cpu_can_disable(i);
 		register_cpu(cpu, i);
 	}