linux-kernel - Re: [PATCH 1/2] x86/cpu: fix BSP detection when running as Xen PV guest

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Date: Thu, 2 May 2024 14:32:14 +0200
From: Jürgen Groß <jgross@...e.com>
To: Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
 x86@...nel.org
Cc: Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/2] x86/cpu: fix BSP detection when running as Xen PV
 guest

On 30.04.24 18:13, Thomas Gleixner wrote:
> On Fri, Apr 05 2024 at 14:34, Juergen Gross wrote:
>> When booting as a Xen PV guest the boot processor isn't detected
>> correctly and the following message is shown:
>>
>>    CPU topo: Boot CPU APIC ID not the first enumerated APIC ID: 0 > 1
>>
>> Additionally this results in one CPU being ignored.
>>
>> Fix that by calling the BSP detection logic when registering the boot
>> CPU's APIC, too.
>>
>> Fixes: 5c5682b9f87a ("x86/cpu: Detect real BSP on crash kernels")
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>>   arch/x86/kernel/cpu/topology.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
>> index aaca8d235dc2..23c3db5e6396 100644
>> --- a/arch/x86/kernel/cpu/topology.c
>> +++ b/arch/x86/kernel/cpu/topology.c
>> @@ -255,7 +255,7 @@ void __init topology_register_boot_apic(u32 apic_id)
>>   	WARN_ON_ONCE(topo_info.boot_cpu_apic_id != BAD_APICID);
>>   
>>   	topo_info.boot_cpu_apic_id = apic_id;
>> -	topo_register_apic(apic_id, CPU_ACPIID_INVALID, true);
>> +	topology_register_apic(apic_id, CPU_ACPIID_INVALID, true);
> 
> No. This does not fix anything at all. It just papers over the
> underlying problem.
> 
> Thanks,
> 
>          tglx
> ---
> diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
> index 27d1a5b7f571..ac41d83b38d3 100644
> --- a/arch/x86/xen/smp_pv.c
> +++ b/arch/x86/xen/smp_pv.c
> @@ -154,9 +154,9 @@ static void __init xen_pv_smp_config(void)
>   	u32 apicid = 0;
>   	int i;
>   
> -	topology_register_boot_apic(apicid++);
> +	topology_register_boot_apic(apicid);
>   
> -	for (i = 1; i < nr_cpu_ids; i++)
> +	for (i = 0; i < nr_cpu_ids; i++)
>   		topology_register_apic(apicid++, CPU_ACPIID_INVALID, true);
>   
>   	/* Pretend to be a proper enumerated system */
> 
>          
> 

Thanks, works great.

Do you want it to send as your patch, or should I add your Signed-off-by or
your Suggested-by?


Juergen