[PATCHv10 15/18] x86/smp: Add smp_ops.stop_this_cpu() callback

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

If the helper is defined, it is called instead of halt() to stop the CPU
at the end of stop_this_cpu() and on crash CPU shutdown.

ACPI MADT will use it to hand over the CPU to BIOS in order to be able
to wake it up again after kexec.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Tao Liu <ltao@redhat.com>
---
 arch/x86/include/asm/smp.h | 1 +
 arch/x86/kernel/process.c  | 7 +++++++
 arch/x86/kernel/reboot.c   | 6 ++++++
 3 files changed, 14 insertions(+)

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index a35936b512fe..ca073f40698f 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -35,6 +35,7 @@ struct smp_ops {
 	int (*cpu_disable)(void);
 	void (*cpu_die)(unsigned int cpu);
 	void (*play_dead)(void);
+	void (*stop_this_cpu)(void);
 
 	void (*send_call_func_ipi)(const struct cpumask *mask);
 	void (*send_call_func_single_ipi)(int cpu);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index b8441147eb5e..f63f8fd00a91 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -835,6 +835,13 @@ void __noreturn stop_this_cpu(void *dummy)
 	 */
 	cpumask_clear_cpu(cpu, &cpus_stop_mask);
 
+#ifdef CONFIG_SMP
+	if (smp_ops.stop_this_cpu) {
+		smp_ops.stop_this_cpu();
+		unreachable();
+	}
+#endif
+
 	for (;;) {
 		/*
 		 * Use native_halt() so that memory contents don't change
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 1ec478f40963..293ded05a4b0 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -880,6 +880,12 @@ static int crash_nmi_callback(unsigned int val, struct pt_regs *regs)
 	cpu_emergency_disable_virtualization();
 
 	atomic_dec(&waiting_for_crash_ipi);
+
+	if (smp_ops.stop_this_cpu) {
+		smp_ops.stop_this_cpu();
+		unreachable();
+	}
+
 	/* Assume hlt works */
 	halt();
 	for (;;)
-- 
2.43.0