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>
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@ -16,6 +16,8 @@
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#include <linux/init.h>
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#include <linux/smp.h>
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#include <linux/of.h>
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#include <linux/delay.h>
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#include <uapi/linux/psci.h>
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#include <asm/psci.h>
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#include <asm/smp_plat.h>
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@ -66,6 +68,36 @@ void __ref psci_cpu_die(unsigned int cpu)
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/* We should never return */
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panic("psci: cpu %d failed to shutdown\n", cpu);
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}
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int __ref psci_cpu_kill(unsigned int cpu)
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{
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int err, i;
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if (!psci_ops.affinity_info)
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return 1;
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/*
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* cpu_kill could race with cpu_die and we can
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* potentially end up declaring this cpu undead
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* while it is dying. So, try again a few times.
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*/
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for (i = 0; i < 10; i++) {
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err = psci_ops.affinity_info(cpu_logical_map(cpu), 0);
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if (err == PSCI_0_2_AFFINITY_LEVEL_OFF) {
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pr_info("CPU%d killed.\n", cpu);
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return 1;
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}
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msleep(10);
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pr_info("Retrying again to check for CPU kill\n");
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}
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pr_warn("CPU%d may not have shut down cleanly (AFFINITY_INFO reports %d)\n",
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cpu, err);
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/* Make platform_cpu_kill() fail. */
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return 0;
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}
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#endif
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bool __init psci_smp_available(void)
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@ -78,5 +110,6 @@ struct smp_operations __initdata psci_smp_ops = {
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.smp_boot_secondary = psci_boot_secondary,
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#ifdef CONFIG_HOTPLUG_CPU
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.cpu_die = psci_cpu_die,
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.cpu_kill = psci_cpu_kill,
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#endif
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};
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@ -39,6 +39,7 @@ struct device_node;
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* from the cpu to be killed.
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* @cpu_die: Makes a cpu leave the kernel. Must not fail. Called from the
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* cpu being killed.
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* @cpu_kill: Ensures a cpu has left the kernel. Called from another cpu.
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* @cpu_suspend: Suspends a cpu and saves the required context. May fail owing
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* to wrong parameters or error conditions. Called from the
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* CPU being suspended. Must be called with IRQs disabled.
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@ -52,6 +53,7 @@ struct cpu_operations {
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#ifdef CONFIG_HOTPLUG_CPU
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int (*cpu_disable)(unsigned int cpu);
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void (*cpu_die)(unsigned int cpu);
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int (*cpu_kill)(unsigned int cpu);
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#endif
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#ifdef CONFIG_ARM64_CPU_SUSPEND
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int (*cpu_suspend)(unsigned long);
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@ -20,6 +20,7 @@
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#include <linux/smp.h>
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#include <linux/reboot.h>
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#include <linux/pm.h>
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#include <linux/delay.h>
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#include <uapi/linux/psci.h>
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#include <asm/compiler.h>
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@ -403,6 +404,35 @@ static void cpu_psci_cpu_die(unsigned int cpu)
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pr_crit("unable to power off CPU%u (%d)\n", cpu, ret);
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}
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static int cpu_psci_cpu_kill(unsigned int cpu)
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{
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int err, i;
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if (!psci_ops.affinity_info)
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return 1;
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/*
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* cpu_kill could race with cpu_die and we can
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* potentially end up declaring this cpu undead
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* while it is dying. So, try again a few times.
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*/
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for (i = 0; i < 10; i++) {
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err = psci_ops.affinity_info(cpu_logical_map(cpu), 0);
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if (err == PSCI_0_2_AFFINITY_LEVEL_OFF) {
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pr_info("CPU%d killed.\n", cpu);
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return 1;
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}
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msleep(10);
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pr_info("Retrying again to check for CPU kill\n");
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}
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pr_warn("CPU%d may not have shut down cleanly (AFFINITY_INFO reports %d)\n",
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cpu, err);
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/* Make op_cpu_kill() fail. */
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return 0;
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}
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#endif
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const struct cpu_operations cpu_psci_ops = {
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@ -413,6 +443,7 @@ const struct cpu_operations cpu_psci_ops = {
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#ifdef CONFIG_HOTPLUG_CPU
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.cpu_disable = cpu_psci_cpu_disable,
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.cpu_die = cpu_psci_cpu_die,
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.cpu_kill = cpu_psci_cpu_kill,
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#endif
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};
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@ -228,6 +228,19 @@ int __cpu_disable(void)
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return 0;
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}
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static int op_cpu_kill(unsigned int cpu)
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{
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/*
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* If we have no means of synchronising with the dying CPU, then assume
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* that it is really dead. We can only wait for an arbitrary length of
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* time and hope that it's dead, so let's skip the wait and just hope.
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*/
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if (!cpu_ops[cpu]->cpu_kill)
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return 1;
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return cpu_ops[cpu]->cpu_kill(cpu);
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}
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static DECLARE_COMPLETION(cpu_died);
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/*
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@ -241,6 +254,15 @@ void __cpu_die(unsigned int cpu)
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return;
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}
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pr_notice("CPU%u: shutdown\n", cpu);
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/*
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* Now that the dying CPU is beyond the point of no return w.r.t.
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* in-kernel synchronisation, try to get the firwmare to help us to
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* verify that it has really left the kernel before we consider
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* clobbering anything it might still be using.
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*/
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if (!op_cpu_kill(cpu))
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pr_warn("CPU%d may not have shut down cleanly\n", cpu);
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}
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/*
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