From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrey Smetanin <asmetanin@virtuozzo.com>
Subject: Re: [PATCH v2 2/5] target-i386/kvm: Hyper-V SynIC MSR's support
Date: Wed, 11 Nov 2015 12:25:12 +0300
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Cc: "Denis V. Lunev" <den@openvz.org>,
	Richard Henderson <rth@twiddle.net>,
	Eduardo Habkost <ehabkost@redhat.com>,
	=?UTF-8?Q?Andreas_F=c3=a4rber?= <afaerber@suse.de>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Roman Kagan <rkagan@virtuozzo.com>, <kvm@vger.kernel.org>
To: Paolo Bonzini <pbonzini@redhat.com>, <qemu-devel@nongnu.org>
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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
>