Re: [Qemu-devel] [PATCH 1/1] hyperv: cpu hotplug fix with HyperV enabled

["Denis V. Lunev" <den@openvz.org>]

On 02/12/2016 02:00 PM, Andreas Färber wrote:
> Am 11.02.2016 um 21:19 schrieb Denis V. Lunev:
>> From: "Alexey V. Kostyushko" <aleksko@virtuozzo.com>
>>
>> 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.
>>
>> Add option 'hv-cpuhotplug' to control this behavior.
>>
>> Signed-off-by: Alexey V. Kostyushko <aleksko@virtuozzo.com>
>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>> CC: Paolo Bonzini <pbonzini@redhat.com>
>> CC: Richard Henderson <rth@twiddle.net>
>> CC: Eduardo Habkost <ehabkost@redhat.com>
>> CC: "Andreas Färber" <afaerber@suse.de>
>> ---
>>   target-i386/cpu-qom.h | 1 +
>>   target-i386/cpu.c     | 1 +
>>   target-i386/kvm.c     | 6 +++++-
>>   3 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/target-i386/cpu-qom.h b/target-i386/cpu-qom.h
>> index 5f9d960..4aec616 100644
>> --- a/target-i386/cpu-qom.h
>> +++ b/target-i386/cpu-qom.h
>> @@ -96,6 +96,7 @@ typedef struct X86CPU {
>>       bool hyperv_runtime;
>>       bool hyperv_synic;
>>       bool hyperv_stimer;
>> +    bool hyperv_cpuhotplug;
>>       bool check_cpuid;
>>       bool enforce_cpuid;
>>       bool expose_kvm;
>> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
>> index b255644..32c38ae 100644
>> --- a/target-i386/cpu.c
>> +++ b/target-i386/cpu.c
>> @@ -3172,6 +3172,7 @@ static Property x86_cpu_properties[] = {
>>       DEFINE_PROP_BOOL("hv-runtime", X86CPU, hyperv_runtime, false),
>>       DEFINE_PROP_BOOL("hv-synic", X86CPU, hyperv_synic, false),
>>       DEFINE_PROP_BOOL("hv-stimer", X86CPU, hyperv_stimer, false),
>> +    DEFINE_PROP_BOOL("hv-cpuhotplug", X86CPU, hyperv_cpuhotplug, false),
> Is "cpuhotplug" some fixed HyperV name? Otherwise we generally use a
> dashes convention for QOM properties, i.e. "hv-cpu-hotplug".
>
> Regards,
> Andreas
This name is for libvirt. We can take one one. This is not a problem.

Roman Kagan has proposed verbally a bit different approach.
He suggests not to introduce the option but
check here that HyperV is enabled (any single option is enough
to face the problem) and CPU hotplug is enabled and automatically
enable this bit.

Paolo, Andreas, is there any opinion on this?

As far as I can see for the time being we lend such decisions to
libvirt. But this bit does not require any processing.

Den