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

[fengchengwen <fengchengwen@xxxxxxxxxx>]

On 3/12/2026 7:02 PM, Peter Zijlstra wrote:
> 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.

This is indeed an issue, it has been fixed in v7 (by treating 
CPU_ACPIID_INVALID as an error).

Thanks

> 
>