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From:   Wanpeng Li <kernellwp@gmail.com>
Date:   Tue, 24 Apr 2018 10:59:04 +0800
Message-ID: <CANRm+CzxG5cm8ECopzGYpF3E3RTjvFGD3_7o8S=tffFxnvYoiA@mail.gmail.com>
Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Eduardo Habkost <ehabkost@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>
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2018-04-18 18:36 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
> On 18/04/2018 11:03, Eduardo Habkost wrote:
>>>> QEMU setting ucode_rev automatically using the host value when
>>>> using "-cpu host" (with no need for explicit ucode_rev option)
>>>> makes sense to me.
>>> QEMU can't get the host value by rdmsr MSR_IA32_UCODE_REV directly
>>> since rdmsr will #GP when ring !=0, any idea?
>> By looking at kvm_get_msr_feature(), it looks like
>> ioctl(system_fd, KVM_GET_MSRS) would return the host MSR value
>> for us.
>
> Yes, that's exactly what it was introduced for (together with other MSRs
> including VMX capabilities).

How about the live migration? What will happen if the source and
destination machines have different microcode version?

Regards,
Wanpeng Li