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

[Jürgen Groß]

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@xxxxxxxx>
> > ---
> >   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