Re: [PATCH 11/19] arm64: smp: Use generic HOTPLUG_SPLIT_STARTUP machinery for CPU onlining

In preparation for enabling parallel bringup of secondary CPUs on arm64,
take the baby step of moving from HOTPLUG_CORE_SYNC_FULL to
HOTPLUG_SPLIT_STARTUP.

Rework the cpu_die_early() path to use a private cpumask, otherwise
clearing the incoming CPU from the present mask in the 'kick' stage will
prevent the hotplug stage machine from progressing and
arch_cpuhp_cleanup_kick_cpu() will not be called.

Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/Kconfig           | 2 +-
 arch/arm64/include/asm/smp.h | 1 +
 arch/arm64/kernel/smp.c      | 9 +++++----
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 89d1f0f2269c..fd8cf792b7fd 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -230,7 +230,7 @@ config ARM64
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_KPROBES
 	select HAVE_KRETPROBES
-	select HOTPLUG_CORE_SYNC_FULL
+	select HOTPLUG_SPLIT_STARTUP
 	select HOTPLUG_SMT if HOTPLUG_CPU
 	select IRQ_DOMAIN
 	select IRQ_FORCED_THREADING

diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
index fe343c30d620..7b986a6a765b 100644
--- a/arch/arm64/include/asm/smp.h
+++ b/arch/arm64/include/asm/smp.h

@@ -89,6 +89,7 @@ asmlinkage void secondary_start_kernel(void);
 struct secondary_data {
 	struct task_struct *task;
 	long status;
+	cpumask_t cpu_died_early_mask;
 };
 
 extern struct secondary_data secondary_data;

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 00362ed6e1ab..c5e9d5d5e003 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c

@@ -62,7 +62,7 @@
  * so we need some other way of telling a new secondary core
  * where to place its SVC stack
  */
-struct secondary_data secondary_data;
+struct secondary_data secondary_data = {};
 /* Number of CPUs which aren't online, but looping in kernel text. */
 static int cpus_stuck_in_kernel;
 

@@ -108,7 +108,7 @@ static int boot_secondary(unsigned int cpu, struct task_struct *idle)
 	return -EOPNOTSUPP;
 }
 
-int __cpu_up(unsigned int cpu, struct task_struct *idle)
+int arch_cpuhp_kick_ap_alive(unsigned int cpu, struct task_struct *idle)
 {
 	int ret;
 

@@ -146,6 +146,8 @@ void arch_cpuhp_cleanup_kick_cpu(unsigned int cpu, bool is_alive)
 		cpus_stuck_in_kernel++;
 		break;
 	case CPU_KILL_ME:
+		if (cpumask_test_cpu(cpu, &secondary_data.cpu_died_early_mask))
+			set_cpu_present(cpu, false);

 		if (!op_cpu_kill(cpu)) {
 			pr_crit("CPU%u: died during early boot\n", cpu);
 			break;

@@ -406,8 +408,7 @@ void __noreturn cpu_die_early(void)
 
 	pr_crit("CPU%d: will not boot\n", cpu);
 
-	/* Mark this CPU absent */
-	set_cpu_present(cpu, 0);
+	cpumask_set_cpu(cpu, &secondary_data.cpu_died_early_mask);
 
 	if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
 		update_cpu_boot_status(CPU_KILL_ME);