Re: [Xen-devel] [PATCH] x86: implement cpu_possible_map

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 28/12/17 14:33, Roger Pau Monne wrote:
> On x86 cpu_possible_map is not defined, so trying to use
> num_possible_cpus will generate link time errors.
>
> This patch defines and fills cpu_possible_map with the current CPUs
> plus the hotpluggable ones.
>
> Note that this is already implemented on ARM.
>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
>  xen/arch/x86/setup.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
> index 99f5d61eb8..d62d232f46 100644
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -86,6 +86,7 @@ size_param("highmem-start", highmem_start);
>  #endif
>  
>  cpumask_t __read_mostly cpu_present_map;
> +cpumask_t __read_mostly cpu_possible_map;
>  
>  unsigned long __read_mostly xen_phys_start;
>  
> @@ -1474,11 +1475,14 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>      {
>          max_cpus = 0;
>          set_nr_cpu_ids(1);
> +        cpumask_set_cpu(0, &cpu_possible_map);
>      }
>      else
>      {
>          set_nr_cpu_ids(max_cpus);
>          max_cpus = nr_cpu_ids;
> +        for ( i = 0; i < nr_cpu_ids; i++ )
> +            cpumask_set_cpu(i, &cpu_possible_map);

There are no concurrency issues, so you can use __cpumask_set_cpu().

However, bitmap_fill(... , nr_cpu_ids) would be far more efficient.

Otherwise, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

>      }
>  
>      /* Low mappings were only needed for some BIOS table parsing. */


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