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

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

On 02/12/2016 02:13 PM, Andreas Färber wrote:
> 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" <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?
> 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).
no. this will not work. I should setup CPUID at the beginning
(before boot) and keep it persistent. Thus either option
coming from libvirt or this bit would be automatically
calculated by QEMU.

I'll check that we could create read-only property to export
the value.

OK. I'll redo this tomorrow if nobody will explicitly say 'no'
today :)

Den