Re: [PATCH 4/4] KVM: x86: lapic: don't allow to set non default apic id when not using x2apic api

Sean Christopherson
2022-03-03T19:49:15Z

On Thu, Mar 03, 2022, Sean Christopherson wrote:
> With your proposed change, KVM_SET_LAPIC will fail and we've broken a functional,
> if sketchy, setup. Is there likely to be such a real-world setup that doesn't
> barf on the inconsistent x2APIC ID? Probably not, but I don't see any reason to
> find out.

I take back the "probably not", this isn't even all that contrived. Prior to the
"migration", the guest will see a consistent x2APIC ID. It's not hard to imagine
a guest that snapshots the ID and never re-reads the value from "hardware".