ARM: Check if a CPU has gone offline

PSCIv0.2 adds a new function called AFFINITY_INFO, which
can be used to query if a specified CPU has actually gone
offline. Calling this function via cpu_kill ensures that
a CPU has quiesced after a call to cpu_die. This helps
prevent the CPU from doing arbitrary bad things when data
or instructions are clobbered (as happens with kexec)
in the window between a CPU announcing that it is dead
and said CPU leaving the kernel.

Signed-off-by: Ashwin Chaugule <ashwin.chaugule@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 31 insertions, 0 deletions

diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
index 90df6e641227..9e9798f91172 100644
--- a/arch/arm64/kernel/psci.c
+++ b/arch/arm64/kernel/psci.c
@@ -20,6 +20,7 @@
 #include <linux/smp.h>
 #include <linux/reboot.h>
 #include <linux/pm.h>
+#include <linux/delay.h>
 #include <uapi/linux/psci.h>
 
 #include <asm/compiler.h>
@@ -403,6 +404,35 @@ static void cpu_psci_cpu_die(unsigned int cpu)
 
 	pr_crit("unable to power off CPU%u (%d)\n", cpu, ret);
 }
+
+static int cpu_psci_cpu_kill(unsigned int cpu)
+{
+	int err, i;
+
+	if (!psci_ops.affinity_info)
+		return 1;
+	/*
+	 * cpu_kill could race with cpu_die and we can
+	 * potentially end up declaring this cpu undead
+	 * while it is dying. So, try again a few times.
+	 */
+
+	for (i = 0; i < 10; i++) {
+		err = psci_ops.affinity_info(cpu_logical_map(cpu), 0);
+		if (err == PSCI_0_2_AFFINITY_LEVEL_OFF) {
+			pr_info("CPU%d killed.\n", cpu);
+			return 1;
+		}
+
+		msleep(10);
+		pr_info("Retrying again to check for CPU kill\n");
+	}
+
+	pr_warn("CPU%d may not have shut down cleanly (AFFINITY_INFO reports %d)\n",
+			cpu, err);
+	/* Make op_cpu_kill() fail. */
+	return 0;
+}
 #endif
 
 const struct cpu_operations cpu_psci_ops = {
@@ -413,6 +443,7 @@ const struct cpu_operations cpu_psci_ops = {
 #ifdef CONFIG_HOTPLUG_CPU
 	.cpu_disable	= cpu_psci_cpu_disable,
 	.cpu_die	= cpu_psci_cpu_die,
+	.cpu_kill	= cpu_psci_cpu_kill,
 #endif
 };