[RFC PATCH 48/49] x86/boot/tboot: Move CPUHP_AP_X86_TBOOT_DYING post stop_machine()

[Frederic Weisbecker]

Between CPUHP_TEARDOWN_CPU and CPUHP_AP_OFFLINE, stop_machine executes
all the teardown callbacks while stopping all CPUs in the system. This
doesn't mix-up well with running RT or isolated tasks.

In order to transition smoothly from global stop_machine to finer
grained synchronization between teardown callbacks and the other CPUs,
a new stop machine post function has been introduced to be executed
after the main one with IRQs still disabled while other CPUs can exit
stop_machine().

tboot waits for all previously outgoing CPUs to be in Wait-For-SIPI mode
when the last secondary CPU goes down.

Although the expectation looks strange because the number in
ap_wfs_count should only match tboot->num_in_wfs + 1 at this hotplug
stage, anyway the CPU can run this wait loop while the other online CPU
is running concurrently.

Move this teardown callback to post stop_machine() accordingly.

Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---
 kernel/cpu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 59ffcd4534c8..87680f7c6493 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1275,7 +1275,7 @@ void clear_tasks_mm_cpumask(int cpu)
 static int take_cpu_down(void *_param)
 {
 	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
-	enum cpuhp_state target = max((int)st->target, CPUHP_AP_TICK_DYING);
+	enum cpuhp_state target = max((int)st->target, CPUHP_AP_X86_TBOOT_DYING);
 	int err, cpu = smp_processor_id();
 
 	/* Ensure this CPU doesn't handle any more interrupts. */
@@ -1303,7 +1303,7 @@ static int take_cpu_down_post(void *_param)
 	enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
 	int cpu = smp_processor_id();
 
-	WARN_ON(st->state != CPUHP_AP_TICK_DYING);
+	WARN_ON(st->state != CPUHP_AP_X86_TBOOT_DYING);
 	/*
 	 * Invoke the former CPU_DYING callbacks. DYING must not fail!
 	 */
-- 
2.53.0