Linux Virtualization - Sep 2020 - [PATCH RFC v1 10/18] x86/hyperv: implement and use hv_smp_prepare_cpus

Wei Liu <wei.liu at kernel.org> writes:
> Microsoft Hypervisor requires the root partition to make a few
> hypercalls to setup application processors before they can be used.
>
> Signed-off-by: Lillian Grassin-Drake <ligrassi at microsoft.com>
> Signed-off-by: Sunil Muthuswamy <sunilmut at microsoft.com>
> Co-Developed-by: Lillian Grassin-Drake <ligrassi at microsoft.com>
> Co-Developed-by: Sunil Muthuswamy <sunilmut at microsoft.com>
> Signed-off-by: Wei Liu <wei.liu at kernel.org>
> ---
> CPU hotplug and unplug is not yet supported in this setup, so those
> paths remain untouched.
> ---
>  arch/x86/kernel/cpu/mshyperv.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/mshyperv.c
b/arch/x86/kernel/cpu/mshyperv.c
> index 1bf57d310f78..7522cae02759 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -203,6 +203,31 @@ static void __init hv_smp_prepare_boot_cpu(void)
>  	hv_init_spinlocks();
>  #endif
>  }
> +
> +static void __init hv_smp_prepare_cpus(unsigned int max_cpus)
> +{
> +#if defined(CONFIG_X86_64)
I think it makes little sense to try to make Linux work as Hyper-V root
partition when !CONFIG_X86_64. If we still care about Hyper-V enablement
for !CONFIG_X86_64 we can probably introduce something like
CONFIG_HYPERV_ROOT and enable it automatically, e.g.

config HYPERV_ROOT
        def_bool HYPERV && X86_64

and use it instead.
> +	int i;
> +	int vp_index = 1;
> +	int ret;
> +
> +	native_smp_prepare_cpus(max_cpus);
> +
> +	for_each_present_cpu(i) {
> +		if (i == 0)
> +			continue;
> +		ret = hv_call_add_logical_proc(numa_cpu_node(i), i, cpu_physical_id(i));
> +		BUG_ON(ret);
> +	}
> +
> +	for_each_present_cpu(i) {
> +		if (i == 0)
> +			continue;
> +		ret = hv_call_create_vp(numa_cpu_node(i), hv_current_partition_id,
vp_index++, i);
So vp_index variable is needed here to make sure there are no gaps? (or
we could've just used 'i')?
> +		BUG_ON(ret);
> +	}
> +#endif
> +}
>  #endif
>  
>  static void __init ms_hyperv_init_platform(void)
> @@ -359,6 +384,8 @@ static void __init ms_hyperv_init_platform(void)
>  
>  # ifdef CONFIG_SMP
>  	smp_ops.smp_prepare_boot_cpu = hv_smp_prepare_boot_cpu;
> +	if (hv_root_partition)
> +		smp_ops.smp_prepare_cpus = hv_smp_prepare_cpus;
>  # endif
>  
>  	/*
-- 
Vitaly