Re: [Xen-devel] [PATCH 1/3] xen/arm: Enable cpu_hotplug.c

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Stefano,

On 14/10/2015 18:49, Stefano Stabellini wrote:
> Build cpu_hotplug for ARM and ARM64 guests.
>
> Rename arch_(un)register_cpu to xen_(un)register_cpu and provide an
> empty implementation on ARM and ARM64. On x86 just call
> arch_(un)register_cpu as we are already doing.
>
> Initialize cpu_hotplug on ARM.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> ---
>   arch/arm/include/asm/xen/hypervisor.h |    8 ++++++++
>   arch/x86/include/asm/xen/hypervisor.h |    5 +++++
>   arch/x86/xen/enlighten.c              |   15 +++++++++++++++
>   drivers/xen/Makefile                  |    2 --
>   drivers/xen/cpu_hotplug.c             |    6 ++++--
>   5 files changed, 32 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/include/asm/xen/hypervisor.h 
> b/arch/arm/include/asm/xen/hypervisor.h
> index 04ff8e7..2bc418a 100644
> --- a/arch/arm/include/asm/xen/hypervisor.h
> +++ b/arch/arm/include/asm/xen/hypervisor.h
> @@ -26,4 +26,12 @@ void __init xen_early_init(void);
>   static inline void xen_early_init(void) { return; }
>   #endif
I know that those helpers are empty for now. But I would prefer to see 
them protected by (FWIW, it's what you did for x86).
#ifdef CONFIG_CPU_HOTPLUG

> +static inline void xen_arch_register_cpu(int num)
> +{
> +}
> +
> +static inline void xen_arch_unregister_cpu(int num)
> +{
> +}
> +
#endif

>   #endif /* _ASM_ARM_XEN_HYPERVISOR_H */
[...]

> diff --git a/drivers/xen/cpu_hotplug.c b/drivers/xen/cpu_hotplug.c
> index cc6513a..122b351 100644
> --- a/drivers/xen/cpu_hotplug.c
> +++ b/drivers/xen/cpu_hotplug.c
> @@ -11,7 +11,7 @@
>   static void enable_hotplug_cpu(int cpu)
>   {
>         if (!cpu_present(cpu))
> -               arch_register_cpu(cpu);
> +               xen_arch_register_cpu(cpu);
>
>         set_cpu_present(cpu, true);
>   }
> @@ -19,7 +19,7 @@ static void enable_hotplug_cpu(int cpu)
>   static void disable_hotplug_cpu(int cpu)
>   {
>         if (cpu_present(cpu))
> -               arch_unregister_cpu(cpu);
> +               xen_arch_unregister_cpu(cpu);
>
>         set_cpu_present(cpu, false);
>   }
> @@ -102,8 +102,10 @@ static int __init setup_vcpu_hotplug_event(void)
>         static struct notifier_block xsn_cpu = {
>                 .notifier_call = setup_cpu_watcher };
>
> +#ifdef CONFIG_X86
>         if (!xen_pv_domain())
>                 return -ENODEV;
> +#endif
For ARM, you need to check if it's a Xen domain. Otherwise a kernel 
aware of Xen won't boot on baremetal.
>         register_xenstore_notifier(&xsn_cpu);
Regards,

--
Julien Grall

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