arm64: smp: Add function to determine if cpus are stuck in the kernel (b69e0dc1) · Commits · e / devices / android_kernel_fairphone_FP4

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 ("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@arm.com> Acked-by:

Mark Rutland <mark.rutland@arm.com> Reviewed-by:

Suzuki K Poulose <suzuki.poulose@arm.com> Signed-off-by:

Will Deacon <will.deacon@arm.com> [catalin.marinas@arm.com: cherry-picked from mainline for kexec dependency] Signed-off-by:

Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/smp.h

+12 −0

Original line number	Diff line number	Diff line
		@@ -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 */

arch/arm64/kernel/smp.c

+18 −0

Original line number	Diff line number	Diff line
		@@ -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;
		}