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

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