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>

diff --git a/arch/arm/kernel/psci_smp.c b/arch/arm/kernel/psci_smp.c
index 570a48c..28a1db4 100644 (file)
--- a/arch/arm/kernel/psci_smp.c
+++ b/arch/arm/kernel/psci_smp.c
@@ -16,6 +16,8 @@
 #include <linux/init.h>
 #include <linux/smp.h>
 #include <linux/of.h>
+#include <linux/delay.h>
+#include <uapi/linux/psci.h>
 
 #include <asm/psci.h>
 #include <asm/smp_plat.h>
@@ -66,6 +68,36 @@ void __ref psci_cpu_die(unsigned int cpu)
        /* We should never return */
        panic("psci: cpu %d failed to shutdown\n", cpu);
 }
+
+int __ref 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 platform_cpu_kill() fail. */
+       return 0;
+}
+
 #endif
 
 bool __init psci_smp_available(void)
@@ -78,5 +110,6 @@ struct smp_operations __initdata psci_smp_ops = {
        .smp_boot_secondary     = psci_boot_secondary,
 #ifdef CONFIG_HOTPLUG_CPU
        .cpu_die                = psci_cpu_die,
+       .cpu_kill               = psci_cpu_kill,
 #endif
 };

diff --git a/arch/arm64/include/asm/cpu_ops.h b/arch/arm64/include/asm/cpu_ops.h
index 1524130..d7b4b38 100644 (file)
--- a/arch/arm64/include/asm/cpu_ops.h
+++ b/arch/arm64/include/asm/cpu_ops.h
@@ -39,6 +39,7 @@ struct device_node;
  *             from the cpu to be killed.
  * @cpu_die:   Makes a cpu leave the kernel. Must not fail. Called from the
  *             cpu being killed.
+ * @cpu_kill:  Ensures a cpu has left the kernel. Called from another cpu.
  * @cpu_suspend: Suspends a cpu and saves the required context. May fail owing
  *               to wrong parameters or error conditions. Called from the
  *               CPU being suspended. Must be called with IRQs disabled.
@@ -52,6 +53,7 @@ struct cpu_operations {
 #ifdef CONFIG_HOTPLUG_CPU
        int             (*cpu_disable)(unsigned int cpu);
        void            (*cpu_die)(unsigned int cpu);
+       int             (*cpu_kill)(unsigned int cpu);
 #endif
 #ifdef CONFIG_ARM64_CPU_SUSPEND
        int             (*cpu_suspend)(unsigned long);

diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
index 90df6e6..9e9798f 100644 (file)
--- 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
 };
 

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index f0a141d..c3cb160 100644 (file)
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -228,6 +228,19 @@ int __cpu_disable(void)
        return 0;
 }
 
+static int op_cpu_kill(unsigned int cpu)
+{
+       /*
+        * If we have no means of synchronising with the dying CPU, then assume
+        * that it is really dead. We can only wait for an arbitrary length of
+        * time and hope that it's dead, so let's skip the wait and just hope.
+        */
+       if (!cpu_ops[cpu]->cpu_kill)
+               return 1;
+
+       return cpu_ops[cpu]->cpu_kill(cpu);
+}
+
 static DECLARE_COMPLETION(cpu_died);
 
 /*
@@ -241,6 +254,15 @@ void __cpu_die(unsigned int cpu)
                return;
        }
        pr_notice("CPU%u: shutdown\n", cpu);
+
+       /*
+        * Now that the dying CPU is beyond the point of no return w.r.t.
+        * in-kernel synchronisation, try to get the firwmare to help us to
+        * verify that it has really left the kernel before we consider
+        * clobbering anything it might still be using.
+        */
+       if (!op_cpu_kill(cpu))
+               pr_warn("CPU%d may not have shut down cleanly\n", cpu);
 }
 
 /*