x86/smpboot: Get rid of cpu_init_secondary()

The synchronization of the AP with the control CPU is a SMP boot problem
and has nothing to do with cpu_init().

Open code cpu_init_secondary() in start_secondary() and move
wait_for_master_cpu() into the SMP boot code.

No functional change.

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Michael Kelley <[email protected]>
Tested-by: Oleksandr Natalenko <[email protected]>
Tested-by: Helge Deller <[email protected]> # parisc
Tested-by: Guilherme G. Piccoli <[email protected]> # Steam Deck
Link: https://lore.kernel.org/r/[email protected]

Author: KAGA-KOKO

arch/x86/include/asm/processor.h

@@ -551,7 +551,6 @@ extern void switch_gdt_and_percpu_base(int);
 extern void load_direct_gdt(int);
 extern void load_fixmap_gdt(int);
 extern void cpu_init(void);
-extern void cpu_init_secondary(void);
 extern void cpu_init_exception_handling(void);
 extern void cr4_init(void);
 

arch/x86/kernel/cpu/common.c

@@ -2123,19 +2123,6 @@ static void dbg_restore_debug_regs(void)
 #define dbg_restore_debug_regs()
 #endif /* ! CONFIG_KGDB */
 
-static void wait_for_master_cpu(int cpu)
-{
-#ifdef CONFIG_SMP
-	/*
-	 * wait for ACK from master CPU before continuing
-	 * with AP initialization
-	 */
-	WARN_ON(cpumask_test_and_set_cpu(cpu, cpu_initialized_mask));
-	while (!cpumask_test_cpu(cpu, cpu_callout_mask))
-		cpu_relax();
-#endif
-}
-
 static inline void setup_getcpu(int cpu)
 {
 	unsigned long cpudata = vdso_encode_cpunode(cpu, early_cpu_to_node(cpu));
@@ -2239,8 +2226,6 @@ void cpu_init(void)
 	struct task_struct *cur = current;
 	int cpu = raw_smp_processor_id();
 
-	wait_for_master_cpu(cpu);
-
 	ucode_cpu_init(cpu);
 
 #ifdef CONFIG_NUMA
@@ -2293,18 +2278,6 @@ void cpu_init(void)
 	load_fixmap_gdt(cpu);
 }
 
-#ifdef CONFIG_SMP
-void cpu_init_secondary(void)
-{
-	/*
-	 * Relies on the BP having set-up the IDT tables, which are loaded
-	 * on this CPU in cpu_init_exception_handling().
-	 */
-	cpu_init_exception_handling();
-	cpu_init();
-}
-#endif
-
 #ifdef CONFIG_MICROCODE_LATE_LOADING
 /**
  * store_cpu_caps() - Store a snapshot of CPU capabilities

arch/x86/kernel/smpboot.c

@@ -220,6 +220,17 @@ static void ap_calibrate_delay(void)
 	cpu_data(smp_processor_id()).loops_per_jiffy = loops_per_jiffy;
 }
 
+static void wait_for_master_cpu(int cpu)
+{
+	/*
+	 * Wait for release by control CPU before continuing with AP
+	 * initialization.
+	 */
+	WARN_ON(cpumask_test_and_set_cpu(cpu, cpu_initialized_mask));
+	while (!cpumask_test_cpu(cpu, cpu_callout_mask))
+		cpu_relax();
+}
+
 /*
  * Activate a secondary processor.
  */
@@ -237,13 +248,16 @@ static void notrace start_secondary(void *unused)
 	load_cr3(swapper_pg_dir);
 	__flush_tlb_all();
 #endif
+	cpu_init_exception_handling();
+
 	/*
-	 * Sync point with wait_cpu_initialized(). Before proceeding through
-	 * cpu_init(), the AP will call wait_for_master_cpu() which sets its
-	 * own bit in cpu_initialized_mask and then waits for the BSP to set
-	 * its bit in cpu_callout_mask to release it.
+	 * Sync point with wait_cpu_initialized(). Sets AP in
+	 * cpu_initialized_mask and then waits for the control CPU
+	 * to release it.
 	 */
-	cpu_init_secondary();
+	wait_for_master_cpu(raw_smp_processor_id());
+
+	cpu_init();
 	rcu_cpu_starting(raw_smp_processor_id());
 	x86_cpuinit.early_percpu_clock_init();