Re: [Xen-devel] [PATCH 3/3] xen/arm: don't try to re-register vcpu_info on cpu_hotplug.

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Stefano,

On 14/10/2015 18:49, Stefano Stabellini wrote:
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> ---
>   arch/arm/xen/enlighten.c |    6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 6c09cc4..59f5421 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -93,6 +93,12 @@ static void xen_percpu_init(void)
>         int err;
>         int cpu = get_cpu();
>
> +       /* vcpu_info already registered, can happen with cpu-hotplug */
Can you please add more comment and explain in the commit message why 
this is necessary for cpu-hotplug?
I had to look at the x86 code to fully understand that it's not possible 
to call VCPUOP_register_vcpu_info twice because there is no hypercall to 
remove the vcpu shared page.

> +       if (per_cpu(xen_vcpu, cpu) != NULL) {
> +               put_cpu();
> +               return;
> +       }
> +
>         pr_info("Xen: initializing cpu%d\n", cpu);
>         vcpup = per_cpu_ptr(xen_vcpu_info, cpu);
Regards,

--
Julien Grall

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