On Thu, Jan 13, 2022 at 10:19:21PM +0000, Sean Christopherson wrote: >On Tue, Jan 11, 2022, Maxim Levitsky wrote: >> Both Intel and AMD's PRM also state that changing APIC ID is implementation >> dependent. >> >> I vote to forbid changing apic id, at least in the case any APIC acceleration >> is used, be that APICv or AVIC. > >That has my vote as well. For IPIv in particular there's not much concern with >backwards compability, i.e. we can tie the behavior to enable_ipiv. Hi Sean and Levitsky, Let's align on the implementation. To disable changes for xAPIC ID when IPIv/AVIC is enabled: 1. introduce a variable (forbid_apicid_change) for this behavior in kvm.ko and export it so that kvm-intel, kvm-amd can set it when IPIv/AVIC is enabled. To reduce complexity, this variable is a module level setting. 2. when guest attempts to change xAPIC ID but it is forbidden, KVM prints a warning on host and injects a #GP to guest. 3. remove AVIC code that deals with changes to xAPIC ID.
