Commit 5c492c3f authored by James Morse's avatar James Morse Committed by Will Deacon

arm64: smp: Add function to determine if cpus are stuck in the kernel

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 44dbcc93 ("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: default avatarJames Morse <james.morse@arm.com>
Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Reviewed-by: default avatarSuzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 20c27a42
......@@ -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 */
......@@ -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;
}
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