From: James Morse <james.morse@xxxxxxx>
kernel/smp.c has a fancy counter that keeps track of the number of CPUs
it marked as not-present and left in cpu_park_loop(). If there are any
CPUs spinning in here, features like kexec or hibernate may release them
by overwriting this memory.
This problem also occurs on machines using spin-tables to release
secondary cores.
After commit 44dbcc93ab67 ("arm64: Fix behavior of maxcpus=N")
we bring all known cpus into the secondary holding pen, meaning this
memory can't be re-used by kexec or hibernate.
Add a function cpus_are_stuck_in_kernel() to determine if either of these
cases have occurred.
Signed-off-by: James Morse <james.morse at arm.com>
Acked-by: Mark Rutland <mark.rutland at arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose at arm.com>
---
arch/arm64/include/asm/smp.h | 12 ++++++++++++
arch/arm64/kernel/smp.c | 18 ++++++++++++++++++
2 files changed, 30 insertions(+)
diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
index 433e504..0226447 100644
--- a/arch/arm64/include/asm/smp.h
+++ b/arch/arm64/include/asm/smp.h
@@ -124,6 +124,18 @@ static inline void cpu_panic_kernel(void)
cpu_park_loop();
}
+/*
+ * If a secondary CPU enters the kernel but fails to come online,
+ * (e.g. due to mismatched features), and cannot exit the kernel,
+ * we increment cpus_stuck_in_kernel and leave the CPU in a
+ * quiesecent loop within the kernel text. The memory containing
+ * this loop must not be re-used for anything else as the 'stuck'
+ * core is executing it.
+ *
+ * This function is used to inhibit features like kexec and hibernate.
+ */
+bool cpus_are_stuck_in_kernel(void);
+
#endif /* ifndef __ASSEMBLY__ */
#endif /* ifndef __ASM_SMP_H */
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 678e084..62ff3c0 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -909,3 +909,21 @@ int setup_profiling_timer(unsigned int multiplier)
{
return -EINVAL;
}
+
+static bool have_cpu_die(void)
+{
+#ifdef CONFIG_HOTPLUG_CPU
+ int any_cpu = raw_smp_processor_id();
+
+ if (cpu_ops[any_cpu]->cpu_die)
+ return true;
+#endif
+ return false;
+}
+
+bool cpus_are_stuck_in_kernel(void)
+{
+ bool smp_spin_tables = (num_possible_cpus() > 1 && !have_cpu_die());
+
+ return !!cpus_stuck_in_kernel || smp_spin_tables;
+}
--
2.5.0
