x86/irq/64: Init hardirq_stack_ptr during CPU hotplug

Preparatory change for disentangling the irq stack union as a
prerequisite for irq stacks with guard pages.

Signed-off-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: "Chang S. Bae" <[e-mail]>
Cc: Dominik Brodowski <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Josh Poimboeuf <[e-mail]>
Cc: Konrad Rzeszutek Wilk <[e-mail]>
Cc: Nicolai Stange <[e-mail]>
Cc: Pavel Tatashin <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Sean Christopherson <[e-mail]>
Cc: x86-ml <[e-mail]>
Cc: Yi Wang <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/x86/include/asm/irq.h

···
 	return ((irq == 2) ? 9 : irq);
 }
 
-#ifdef CONFIG_X86_32
 extern int irq_init_percpu_irqstack(unsigned int cpu);
-#else
-static inline int irq_init_percpu_irqstack(unsigned int cpu) { return 0; }
-#endif
 
 #define __ARCH_HAS_DO_SOFTIRQ
 

arch/x86/kernel/cpu/common.c

···
 	&init_task;
 EXPORT_PER_CPU_SYMBOL(current_task);
 
-DEFINE_PER_CPU(char *, hardirq_stack_ptr) =
-	init_per_cpu_var(irq_stack_union.irq_stack) + IRQ_STACK_SIZE;
-
+DEFINE_PER_CPU(char *, hardirq_stack_ptr);
 DEFINE_PER_CPU(unsigned int, irq_count) __visible = -1;
 
 DEFINE_PER_CPU(int, __preempt_count) = INIT_PREEMPT_COUNT;

arch/x86/kernel/irq_64.c

···
 	generic_handle_irq_desc(desc);
 	return true;
 }
+
+static int map_irq_stack(unsigned int cpu)
+{
+	void *va = per_cpu_ptr(irq_stack_union.irq_stack, cpu);
+
+	per_cpu(hardirq_stack_ptr, cpu) = va + IRQ_STACK_SIZE;
+	return 0;
+}
+
+int irq_init_percpu_irqstack(unsigned int cpu)
+{
+	if (per_cpu(hardirq_stack_ptr, cpu))
+		return 0;
+	return map_irq_stack(cpu);
+}