[PATCH 6/7] ARM: B15: Register reboot notifier for KEXEC

From: Florian Fainelli
Date: Wed Jan 18 2017 - 15:31:12 EST


During kexec, we will go through kernel_kexec() -> syscore_suspend() if
CONFIG_KEXEC_JUMP is set, if not, down the road we end-up calling
kernel_restart_prepare() which invokes reboot notifiers with
SYS_RESTART.

We register a reboot notifier to make sure that the B15 read-ahead cache
is disabled, since it is another level of instruction and data cache,
and we want to avoid any potential side effects with booting a new
kernel with such a cache still turned on.

Signed-off-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
---
arch/arm/mm/cache-b15-rac.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 44 insertions(+)

diff --git a/arch/arm/mm/cache-b15-rac.c b/arch/arm/mm/cache-b15-rac.c
index ef5e93e4b5c2..148d51fdfc3d 100644
--- a/arch/arm/mm/cache-b15-rac.c
+++ b/arch/arm/mm/cache-b15-rac.c
@@ -16,6 +16,7 @@
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/syscore_ops.h>
+#include <linux/reboot.h>

#include <asm/cacheflush.h>
#include <asm/hardware/cache-b15-rac.h>
@@ -151,6 +152,29 @@ static void b15_rac_enable(void)
__b15_rac_enable(enable);
}

+static int b15_rac_reboot_notifier(struct notifier_block *nb,
+ unsigned long action,
+ void *data)
+{
+ /* During kexec, we are not yet migrated on the boot CPU, so we need to
+ * make sure we are SMP safe here. Once the RAC is disabled, flag it as
+ * suspended such that the hotplug notifier returns early.
+ */
+ if (action == SYS_RESTART) {
+ spin_lock(&rac_lock);
+ b15_rac_disable_and_flush();
+ clear_bit(RAC_ENABLED, &b15_rac_flags);
+ set_bit(RAC_SUSPENDED, &b15_rac_flags);
+ spin_unlock(&rac_lock);
+ }
+
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block b15_rac_reboot_nb = {
+ .notifier_call = b15_rac_reboot_notifier,
+};
+
#ifdef CONFIG_HOTPLUG_CPU
/* The CPU hotplug case is the most interesting one, we basically need to make
* sure that the RAC is disabled for the entire system prior to having a CPU
@@ -191,6 +215,12 @@ static void b15_rac_enable(void)
/* Running on the dying CPU */
static int b15_rac_dying_cpu(unsigned int cpu)
{
+ /* During kexec/reboot, the RAC is disabled via the reboot notifier
+ * return early here.
+ */
+ if (test_bit(RAC_SUSPENDED, &b15_rac_flags))
+ return 0;
+
spin_lock(&rac_lock);

/* Indicate that we are starting a hotplug procedure */
@@ -207,6 +237,12 @@ static int b15_rac_dying_cpu(unsigned int cpu)
/* Running on a non-dying CPU */
static int b15_rac_dead_cpu(unsigned int cpu)
{
+ /* During kexec/reboot, the RAC is disabled via the reboot notifier
+ * return early here.
+ */
+ if (test_bit(RAC_SUSPENDED, &b15_rac_flags))
+ return 0;
+
spin_lock(&rac_lock);

/* And enable it */
@@ -272,6 +308,13 @@ static int __init b15_rac_init(void)
goto out;
}

+ ret = register_reboot_notifier(&b15_rac_reboot_nb);
+ if (ret) {
+ pr_err("failed to register reboot notifier\n");
+ iounmap(b15_rac_base);
+ goto out;
+ }
+
#ifdef CONFIG_HOTPLUG_CPU
ret = cpuhp_setup_state_nocalls(CPUHP_AP_ARM_CACHE_B15_RAC_DEAD,
"arm/cache-b15-rac:dead",
@@ -308,6 +351,7 @@ static int __init b15_rac_init(void)
out_cpu_dead:
cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CACHE_B15_RAC_DYING);
out_unmap:
+ unregister_reboot_notifier(&b15_rac_reboot_nb);
iounmap(b15_rac_base);
out:
of_node_put(dn);
--
2.9.3