Re: [PATCHv6 14/16] x86/smp: Add smp_ops.stop_this_cpu() callback

["Huang, Kai" <kai.huang@intel.com>]

On Wed, 2024-01-24 at 14:55 +0200, Kirill A. Shutemov wrote:
> 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>

> ---
>  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 4fab2ed454f3..390d53fd34f9 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -38,6 +38,7 @@ 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 ab49ade31b0d..00c1b957476d 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 0574d4ad6b41..0a75efe579c0 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 (;;)