Re: [PATCH] KVM: X86: Allow userspace to define the microcode version

Konrad Rzeszutek Wilk
2018-04-24T13:45:50Z

On April 24, 2018 1:09:00 AM EDT, Paolo Bonzini <pbonzini@redhat.com> wrote:
>On 24/04/2018 05:14, Konrad Rzeszutek Wilk wrote:
>> You would need to include the microcode version in the migration
>stream.
>>
>> But this brings another point - what if we want to manifest certain
>> new CPUID bits?
>
>You don't do that across migration. Generally if you want to do live
>migration and you set up the guest to know everything about the host
>(down to the microcode level), you should make sure your host are
>pretty
>much identical.

I understand how it ought to be but sadly the cloud vendors have a mix of hardware.

With the retpoline/IBRS support (like what RH kernel has) you could migrate from Skylake to Broadwell and switching over from IBRS to retpoline would be good.

Hence asking about this.

>
>Paolo