Awesome - can confirm the patch does indeed make the machine boot. Full
dmesg from boot attached. And the contents of
/sys/kernel/debug/x86/topo/ is as follows:

domain: Thread     shift: 1 dom_size:     2 max_threads:     2
domain: Core       shift: 4 dom_size:     8 max_threads:    16
domain: Module     shift: 4 dom_size:     1 max_threads:    16
domain: Tile       shift: 4 dom_size:     1 max_threads:    16
domain: Die        shift: 4 dom_size:     1 max_threads:    16
domain: DieGrp     shift: 4 dom_size:     1 max_threads:    16
domain: Package    shift: 4 dom_size:     1 max_threads:    16

On Thu, 2024-04-18 at 21:13 +0200, Thomas Gleixner wrote:
> On Thu, Apr 18 2024 at 13:20, Lyude Paul wrote:
> 
> > Just gave it a try, unfortunately I'm still seeing the same result
> > on
> > that branch.
> > 
> > One more piece of information I apparently missed when reporting
> > this
> > yesterday btw: I noticed one more kernel message that comes before
> > the
> > panic that's probably relevant:
> > 
> > ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
> 
> Can you please apply the debug patch below which should make it boot
> again.
> 
> Please also provide the output of the files underneath of
> 
>        /sys/kernel/debug/x86/topo/
> 
> Thanks,
> 
>         tglx
> ---
>  arch/x86/kernel/cpu/topology.c |    7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> --- a/arch/x86/kernel/cpu/topology.c
> +++ b/arch/x86/kernel/cpu/topology.c
> @@ -176,6 +176,8 @@ static __init void topo_register_apic(u3
>  {
>  	int cpu, dom;
>  
> +	pr_info("APIC ID %x present %d\n", apic_id, present);
> +
>  	if (present) {
>  		set_bit(apic_id, phys_cpu_present_map);
>  
> @@ -201,10 +203,7 @@ static __init void topo_register_apic(u3
>  		 */
>  		if (hypervisor_is_type(X86_HYPER_NATIVE) &&
>  		    topo_unit_count(pkgid, TOPO_PKG_DOMAIN,
> phys_cpu_present_map)) {
> -			pr_info_once("Ignoring hot-pluggable APIC ID
> %x in present package.\n",
> -				     apic_id);
> -			topo_info.nr_rejected_cpus++;
> -			return;
> +			pr_info("Hot-pluggable APIC ID %x in present
> package.\n", apic_id);
>  		}
>  
>  		topo_info.nr_disabled_cpus++;
> 
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat