On April 24, 2018 1:09:00 AM EDT, Paolo Bonzini <pbonzini@xxxxxxxxxx> 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
