Re: [patch 24/53] x86/cpu/topology: Provide separate APIC registration functions

["Zhang, Rui" <rui.zhang@intel.com>]

On Mon, 2023-08-07 at 15:53 +0200, Thomas Gleixner wrote:
> generic_processor_info() aside of being a complete misnomer is used
> for
> both early boot registration and ACPI CPU hotplug.
> 
> While it's arguable that this can share some code, it results in code
> which
> is hard to understand and kept around post init for no real reason.
> 
> Also the call sites do lots of manual fiddling in topology related
> variables instead of having proper interfaces for the purpose which
> handle
> the topology internals correctly.
> 
> Provide topology_register_apic(), topology_hotplug_apic() and
> topology_hot_unplug_apic()

s/topology_hot_unplug_apic/topology_hotunplug_apic

thanks,
rui

>  which have the extra magic of the call sites
> incorporated and for now are wrappers around
> generic_processor_info().
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  arch/x86/include/asm/apic.h         |    3 
>  arch/x86/kernel/cpu/topology.c |  113
> ++++++++++++++++++++++++++++++------
>  2 files changed, 98 insertions(+), 18 deletions(-)
> 
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -171,7 +171,10 @@ extern bool apic_needs_pit(void);
>  
>  extern void apic_send_IPI_allbutself(unsigned int vector);
>  
> +extern void topology_register_apic(u32 apic_id, u32 acpi_id, bool
> present);
>  extern void topology_register_boot_apic(u32 apic_id);
> +extern int topology_hotplug_apic(u32 apic_id, u32 acpi_id);
> +extern void topology_hotunplug_apic(unsigned int cpu);
>  
>  #else /* !CONFIG_X86_LOCAL_APIC */
>  static inline void lapic_shutdown(void) { }
> --- a/arch/x86/kernel/cpu/topology.c
> +++ b/arch/x86/kernel/cpu/topology.c
> @@ -79,32 +79,38 @@ early_initcall(smp_init_primary_thread_m
>  static inline void cpu_mark_primary_thread(unsigned int cpu,
> unsigned int apicid) { }
>  #endif
>  
> -/*
> - * Should use this API to allocate logical CPU IDs to keep
> nr_logical_cpuids
> - * and cpuid_to_apicid[] synchronized.
> - */
> -static int allocate_logical_cpuid(int apicid)
> +static int topo_lookup_cpuid(u32 apic_id)
>  {
>         int i;
>  
> -       /*
> -        * cpuid <-> apicid mapping is persistent, so when a cpu is
> up,
> -        * check if the kernel has allocated a cpuid for it.
> -        */
> +       /* CPU# to APICID mapping is persistent once it is
> established */
>         for (i = 0; i < nr_logical_cpuids; i++) {
> -               if (cpuid_to_apicid[i] == apicid)
> +               if (cpuid_to_apicid[i] == apic_id)
>                         return i;
>         }
> +       return -ENODEV;
> +}
> +
> +/*
> + * Should use this API to allocate logical CPU IDs to keep
> nr_logical_cpuids
> + * and cpuid_to_apicid[] synchronized.
> + */
> +static int allocate_logical_cpuid(u32 apic_id)
> +{
> +       int cpu = topo_lookup_cpuid(apic_id);
> +
> +       if (cpu >= 0)
> +               return cpu;
>  
>         /* Allocate a new cpuid. */
>         if (nr_logical_cpuids >= nr_cpu_ids) {
>                 WARN_ONCE(1, "APIC: NR_CPUS/possible_cpus limit of %u
> reached. "
>                              "Processor %d/0x%x and the rest are
> ignored.\n",
> -                            nr_cpu_ids, nr_logical_cpuids, apicid);
> +                            nr_cpu_ids, nr_logical_cpuids, apic_id);
>                 return -EINVAL;
>         }
>  
> -       cpuid_to_apicid[nr_logical_cpuids] = apicid;
> +       cpuid_to_apicid[nr_logical_cpuids] = apic_id;
>         return nr_logical_cpuids++;
>  }
>  
> @@ -122,12 +128,6 @@ static void cpu_update_apic(int cpu, u32
>                 cpu_mark_primary_thread(cpu, apicid);
>  }
>  
> -void __init topology_register_boot_apic(u32 apic_id)
> -{
> -       cpuid_to_apicid[0] = apic_id;
> -       cpu_update_apic(0, apic_id);
> -}
> -
>  int generic_processor_info(int apicid)
>  {
>         int cpu, max = nr_cpu_ids;
> @@ -169,6 +169,83 @@ int generic_processor_info(int apicid)
>         return cpu;
>  }
>  
> +/**
> + * topology_register_apic - Register an APIC in early topology maps
> + * @apic_id:   The APIC ID to set up
> + * @acpi_id:   The ACPI ID associated to the APIC
> + * @present:   True if the corresponding CPU is present
> + */
> +void __init topology_register_apic(u32 apic_id, u32 acpi_id, bool
> present)
> +{
> +       int cpu;
> +
> +       if (apic_id >= MAX_LOCAL_APIC) {
> +               pr_err_once("APIC ID %x exceeds kernel limit of:
> %x\n", apic_id, MAX_LOCAL_APIC - 1);
> +               return;
> +       }
> +
> +       if (!present) {
> +               disabled_cpus++;
> +               return;
> +       }
> +
> +       cpu = generic_processor_info(apic_id);
> +       if (cpu >= 0)
> +               early_per_cpu(x86_cpu_to_acpiid, cpu) = acpi_id;
> +}
> +
> +/**
> + * topology_register_boot_apic - Register the boot CPU APIC
> + * @apic_id:   The APIC ID to set up
> + *
> + * Separate so CPU #0 can be assigned
> + */
> +void __init topology_register_boot_apic(u32 apic_id)
> +{
> +       cpuid_to_apicid[0] = apic_id;
> +       cpu_update_apic(0, apic_id);
> +}
> +
> +#ifdef CONFIG_ACPI_HOTPLUG_CPU
> +/**
> + * topology_hotplug_apic - Handle a physical hotplugged APIC after
> boot
> + * @apic_id:   The APIC ID to set up
> + * @acpi_id:   The ACPI ID associated to the APIC
> + */
> +int topology_hotplug_apic(u32 apic_id, u32 acpi_id)
> +{
> +       int cpu;
> +
> +       if (apic_id >= MAX_LOCAL_APIC)
> +               return -EINVAL;
> +
> +       cpu = topo_lookup_cpuid(apic_id);
> +       if (cpu < 0) {
> +               cpu = generic_processor_info(apic_id);
> +               if (cpu >= 0)
> +                       per_cpu(x86_cpu_to_acpiid, cpu) = acpi_id;
> +       }
> +       return cpu;
> +}
> +
> +/**
> + * topology_hotunplug_apic - Remove a physical hotplugged APIC after
> boot
> + * @cpu:       The CPU number for which the APIC ID is removed
> + */
> +void topology_hotunplug_apic(unsigned int cpu)
> +{
> +       u32 apic_id = cpuid_to_apicid[cpu];
> +
> +       if (apic_id == BAD_APICID)
> +               return;
> +
> +       per_cpu(x86_cpu_to_apicid, cpu) = BAD_APICID;
> +       clear_bit(apic_id, phys_cpu_present_map);
> +       set_cpu_present(cpu, false);
> +       num_processors--;
> +}
> +#endif
> +
>  static int __init apic_set_disabled_cpu_apicid(char *arg)
>  {
>         if (!arg || !get_option(&arg, &disabled_cpu_apicid))
>