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From: "Denis V. Lunev" <den@openvz.org>
Message-ID: <56C48CFE.6040507@openvz.org>
Date: Wed, 17 Feb 2016 18:08:46 +0300
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Subject: Re: [Qemu-devel] [PATCH v2 1/1] hyperv: cpu hotplug fix with HyperV
	enabled
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Cc: Paolo Bonzini <pbonzini@redhat.com>, =?UTF-8?Q?Andreas_F=c3=a4rber?= <afaerber@suse.de>, qemu-devel@nongnu.org, Eduardo Habkost <ehabkost@redhat.com>, Richard Henderson <rth@twiddle.net>

On 02/13/2016 03:00 PM, Denis V. Lunev wrote:
> With Hyper-V enabled CPU hotplug stops working. The CPU appears in device
> manager on Windows but does not appear in peformance monitor and control
> panel.
>
> The root of the problem is the following. Windows checks
> HV_X64_CPU_DYNAMIC_PARTITIONING_AVAILABLE bit in CPUID. The presence of
> this bit is enough to cure the situation.
>
> The bit should be set when CPU hotplug is allowed for HyperV VM. The check
> that hot_add_cpu callback is defined is enough from the protocol point
> of view. Though this callback is defined almost always thus there is no
> need to export that knowledge in the other way.
>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
> CC: Paolo Bonzini <pbonzini@redhat.com>
> CC: Richard Henderson <rth@twiddle.net>
> CC: Eduardo Habkost <ehabkost@redhat.com>
> CC: "Andreas Färber" <afaerber@suse.de>
> ---
> Changes from v1:
> - dropped command line option and set the bit if HyperV is enabled and
>    hot_add_cpu callback is present
>
>   target-i386/kvm.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 94024bc..63dee9c 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -639,6 +639,9 @@ int kvm_arch_init_vcpu(CPUState *cs)
>           if (cpu->hyperv_crash && has_msr_hv_crash) {
>               c->edx |= HV_X64_GUEST_CRASH_MSR_AVAILABLE;
>           }
> +        if (MACHINE_GET_CLASS(current_machine)->hot_add_cpu != NULL) {
> +            c->edx |= HV_X64_CPU_DYNAMIC_PARTITIONING_AVAILABLE;
> +        }
>           if (cpu->hyperv_reset && has_msr_hv_reset) {
>               c->eax |= HV_X64_MSR_RESET_AVAILABLE;
>           }
ping