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ARM: Check if a CPU has gone offline

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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>
This commit is contained in:
Ashwin Chaugule
2014-05-07 10:18:36 -04:00
parent e1cd3b361a
commit c814ca029e
4 changed files with 88 additions and 0 deletions
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31
arch/arm64/kernel/psci.c
View File

@@ -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
};

22
arch/arm64/kernel/smp.c
View File

@@ -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);
}
/*