Re: [PATCH v6 2/3] x86: Implement acpi_get_cpu_uid()

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Thu, Mar 12, 2026 at 03:23:15PM +0800, Chengwen Feng wrote:
> Add acpi_get_cpu_uid() implementation for x86, replacing the existing
> cpu_acpi_id() function. This completes the unified ACPI Processor UID
> retrieval interface across all ACPI-enabled architectures.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Chengwen Feng <fengchengwen@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/cpu.h   |  1 -
>  arch/x86/include/asm/smp.h   |  1 -
>  arch/x86/kernel/cpu/common.c | 15 +++++++++++++++
>  arch/x86/xen/enlighten_hvm.c |  5 +++--
>  include/linux/acpi.h         |  2 --
>  5 files changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
> index ad235dda1ded..57a0786dfd75 100644
> --- a/arch/x86/include/asm/cpu.h
> +++ b/arch/x86/include/asm/cpu.h
> @@ -11,7 +11,6 @@
>  
>  #ifndef CONFIG_SMP
>  #define cpu_physical_id(cpu)                 boot_cpu_physical_apicid
> -#define cpu_acpi_id(cpu)                     0
>  #endif /* CONFIG_SMP */
>  
>  #ifdef CONFIG_HOTPLUG_CPU
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index 84951572ab81..05d1d479b4cf 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -130,7 +130,6 @@ __visible void smp_call_function_interrupt(struct pt_regs 
> *regs);
>  __visible void smp_call_function_single_interrupt(struct pt_regs *r);
>  
>  #define cpu_physical_id(cpu) per_cpu(x86_cpu_to_apicid, cpu)
> -#define cpu_acpi_id(cpu)     per_cpu(x86_cpu_to_acpiid, cpu)
>  
>  /*
>   * This function is needed by all SMP systems. It must _always_ be valid
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 1c3261cae40c..3081557542c7 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -28,6 +28,7 @@
>  #include <linux/stackprotector.h>
>  #include <linux/utsname.h>
>  #include <linux/efi.h>
> +#include <linux/acpi.h>
>  
>  #include <asm/alternative.h>
>  #include <asm/cmdline.h>
> @@ -57,6 +58,7 @@
>  #include <asm/asm.h>
>  #include <asm/bugs.h>
>  #include <asm/cpu.h>
> +#include <asm/smp.h>
>  #include <asm/mce.h>
>  #include <asm/msr.h>
>  #include <asm/cacheinfo.h>
> @@ -2643,3 +2645,16 @@ void __init arch_cpu_finalize_init(void)
>        */
>       mem_encrypt_init();
>  }
> +
> +int acpi_get_cpu_uid(unsigned int cpu, u32 *uid)
> +{
> +     if (cpu >= nr_cpu_ids)
> +             return -EINVAL;
> +#ifndef CONFIG_SMP
> +     *uid = 0;
> +#else
> +     *uid = per_cpu(x86_cpu_to_acpiid, cpu);
> +#endif
> +     return 0;
> +}
> +EXPORT_SYMBOL_GPL(acpi_get_cpu_uid);
> diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
> index fe57ff85d004..2f9fa27e5a3c 100644
> --- a/arch/x86/xen/enlighten_hvm.c
> +++ b/arch/x86/xen/enlighten_hvm.c
> @@ -151,6 +151,7 @@ static void xen_hvm_crash_shutdown(struct pt_regs *regs)
>  
>  static int xen_cpu_up_prepare_hvm(unsigned int cpu)
>  {
> +     u32 cpu_uid;
>       int rc = 0;
>  
>       /*
> @@ -161,8 +162,8 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu)
>        */
>       xen_uninit_lock_cpu(cpu);
>  
> -     if (cpu_acpi_id(cpu) != CPU_ACPIID_INVALID)
> -             per_cpu(xen_vcpu_id, cpu) = cpu_acpi_id(cpu);
> +     if (acpi_get_cpu_uid(cpu, &cpu_uid) == 0)
> +             per_cpu(xen_vcpu_id, cpu) = cpu_uid;
>       else
>               per_cpu(xen_vcpu_id, cpu) = cpu;
>       xen_vcpu_setup(cpu);

This doesn't look right, it will now set CPU_ACPIID_INVALID, while
previously it would not.