x86/smp: Add smp_ops.stop_this_cpu() callback

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 <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Acked-by: Kai Huang <[email protected]>
Tested-by: Tao Liu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: kiryl

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);

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

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 (;;)