Re: [Qemu-devel] [PATCH v2 2/5] target-i386/kvm: Hyper-V SynIC MSR's support

[Andrey Smetanin <asmetanin@virtuozzo.com>]

On 11/11/2015 12:17 PM, Paolo Bonzini wrote:
>
>
> On 11/11/2015 10:09, Andrey Smetanin wrote:
>>>
>>> I would prefer to put this in kvm_arch_init_vcpu, if possible.
>>>
>> Ok. I think the kvm_arch_init_vcpu() is called after migration restores
>> cpu->env->msr_hv_synic_* values, so unconditional initialization of
>> cpu->env->msr_hv_synic_* values can overwrite migrated values. The check
>> "if (!env->msr_hv_synic_version) {" is neccessary for first time
>> initialization to protect against such overwriting. This is why this
>> code migrates 'msr_hv_synic_version' value.
>
> No, kvm_arch_init_vcpu is called at the very beginning, when the VCPU
> thread is created.
>
> main
> -> machine_class->init
> -> pc_init1
> -> pc_cpus_init
> -> pc_new_cpu
> -> cpu_x86_create
> -> object_property_set_bool
> -> x86_cpu_realizefn
> -> qemu_init_vcpu
> -> qemu_kvm_start_vcpu
> -> qemu_kvm_cpu_thread_fn (in new thread)
> -> kvm_init_vcpu
> -> kvm_arch_init_vcpu
>
> This is long before qemu_start_incoming_migration, which is among the
> last things done before calling main_loop
In this case I'll remove migration of msr_hv_synic_version and make 
first time initialization inside  kvm_arch_init_vcpu() - inside section 
where SynIC availability cpuid bit is set.

Thank you for clarification.
>
> Paolo
>