Re: [Qemu-devel] [PATCH 1/1] cpu: report hyperv feature words through qom

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

On 06/14/2016 10:59 PM, Eduardo Habkost wrote:
> On Tue, Jun 14, 2016 at 01:28:40PM +0300, Denis V. Lunev wrote:
>> From: Evgeny Yakovlev <eyakovlev@virtuozzo.com>
>>
>> This change adds hyperv feature words report through qom rpc.
>>
>> When VM is configured with hyperv features enabled libvirt will check that
>> required featured words are set in cpuid leaf 40000003 through qom
>> request.
>>
>> Currently qemu does not report hyperv feature words which prevents windows
>> guests from starting with libvirt.
>>
>> Signed-off-by: Evgeny Yakovlev <eyakovlev@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: Marcelo Tosatti <mtosatti@redhat.com>
> Which QEMU version did you use to test this? Some of those properties already
> exist. See:
>
>    static Property x86_cpu_properties[] = {
>        [...]
>        { .name  = "hv-spinlocks", .info  = &qdev_prop_spinlocks },
>        DEFINE_PROP_BOOL("hv-relaxed", X86CPU, hyperv_relaxed_timing, false),
>        DEFINE_PROP_BOOL("hv-vapic", X86CPU, hyperv_vapic, false),
>        DEFINE_PROP_BOOL("hv-time", X86CPU, hyperv_time, false),
>        DEFINE_PROP_BOOL("hv-crash", X86CPU, hyperv_crash, false),
>        DEFINE_PROP_BOOL("hv-reset", X86CPU, hyperv_reset, false),
>        DEFINE_PROP_BOOL("hv-vpindex", X86CPU, hyperv_vpindex, false),
>        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_STRING("hv-vendor-id", X86CPU, hyperv_vendor_id),
>        DEFINE_PROP_END_OF_LIST()
>    };
>
> QEMU will crash if you try to register the properties twice:
>
>    $ ./x86_64-softmmu/qemu-system-x86_64
>    qemu-system-x86_64: /home/ehabkost/rh/proj/virt/qemu/target-i386/cpu.c:3094: x86_cpu_register_bit_prop: Assertion `fp->ptr == field' failed.
>    Aborted (core dumped)
>
> I like the idea of moving hyperv feature information inside the features array,
> though.
no, idea is a bit different.

The user selects properties in the command line to enable
different HyperV enlightenments. This is how we do that
and this is how the QEMU is expected to work.

After that libvirt starts to check that these properties do
work. In order to do that it executes qom-get and expects
to find enabled HyperV enlightenments in the guest CPUID.

This is the idea of this patch.