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SubjectRe: [PATCH RFC v1 10/18] x86/hyperv: implement and use hv_smp_prepare_cpus
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Wei Liu <wei.liu@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@microsoft.com>
> Signed-off-by: Sunil Muthuswamy <sunilmut@microsoft.com>
> Co-Developed-by: Lillian Grassin-Drake <ligrassi@microsoft.com>
> Co-Developed-by: Sunil Muthuswamy <sunilmut@microsoft.com>
> Signed-off-by: Wei Liu <wei.liu@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

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