Re: Expose support for HyperV features via QMP

[Vitaly Kuznetsov]

Alex Bennée <alex.bennee@linaro.org> writes:

> "manish.mishra" <manish.mishra@nutanix.com> writes:
>
>> Hi Everyone,
>>
>> Checking if there is any feedback on this.
>
> I've expanded the CC list to some relevant maintainers and people who
> have touched that code in case this was missed.
>
>> Thanks
>>
>> Manish Mishra
>>
>> On 31/01/23 8:17 pm, manish.mishra wrote:
>>
>>  Hi Everyone,
>>  I hope everyone is doing great. We wanted to check why we do not expose 
>> support for HyperV features in
>>  Qemu similar to what we do for normal CPU features via query-cpu-defs or 
>> cpu-model-expansion QMP
>>  commands. This support is required for live migration with HyperV features 
>> as hyperv passthrough is not
>>  an option. If users had knowledge of what features are supported by source 
>> and destination, VM can be
>>  started with an intersection of features supported by both source and 
>> destination.
>>  If there is no specific reason for not doing this, does it make sense to 
>> add a new QMP which expose
>>  support (internally also validating with KVM or KVM_GET_SUPPORTED_HV_CPUID 
>> ioctl) for HyperV
>>  features.
>>  Apologies in advance if i misunderstood something.
>>

Thanks for Ccing me. 

Hyper-V features should appear in QMP since

commit 071ce4b03becf9e2df6b758fde9609be8ddf56f1
Author: Vitaly Kuznetsov <vkuznets@redhat.com>
Date:   Tue Jun 8 14:08:13 2021 +0200

    i386: expand Hyper-V features during CPU feature expansion time

also, the support for Hypre-V feature discovery was just added to
libvirt:

903ea9370d qemu_capabilities: Report Hyper-V Enlightenments in domcapabilities
10f4784864 qemu_capabilities: Query for Hyper-V Enlightenments
ff8731680b qemuMonitorJSONGetCPUModelExpansion: Introduce @hv_passthrough 
argument
7c12eb2397 qemuMonitorJSONMakeCPUModel: Introduce @hv_passthrough argument
7c1ecfd512 domain_capabilities: Expose Hyper-V Enlightenments
179e45d237 virDomainCapsEnumFormat: Retrun void
a7789d9324 virDomainCapsEnumFormat: Switch to virXMLFormatElement()

in case this is not enough, could you please elaborate on the use-case
you have in mind?

-- 
Vitaly