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

[Andreas Färber]

Am 12.02.2016 um 12:08 schrieb Denis V. Lunev:
> 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" <address@hidden>
>>>
>>> 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 <address@hidden>
>>> Signed-off-by: Denis V. Lunev <address@hidden>
>>> CC: Paolo Bonzini <address@hidden>
>>> CC: Richard Henderson <address@hidden>
>>> CC: Eduardo Habkost <address@hidden>
>>> CC: "Andreas Färber" <address@hidden>
>>> ---
>>>   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?

That implicit proposal sounds even more appealing to me, yes.

You could still additionally do a dynamic property though, in case you
want to inspect or toggle it at runtime (no clue when Windows reads it).

Andreas

> 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


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