On Thu, Jan 13, 2022, Vitaly Kuznetsov wrote: > Maxim Levitsky <mlevitsk@xxxxxxxxxx> writes: > > For my nested AVIC work I would really want the APIC ID of a VCPU to be read-only > > and be equal to vcpu_id. > > > > Doesn't APIC ID have topology encoded in it? Yeah, APIC IDs are derived from the topology. From the SDM (this doesn't talk about core/SMT info, but that's included as well): The hardware assigned APIC ID is based on system topology and includes encoding for socket position and cluster information. The SDM also says: Some processors permit software to modify the APIC ID. However, the ability of software to modify the APIC ID is processor model specific. So I _think_ we could define KVM behavior to ignore writes from the _guest_, but the APIC_ID == vcpu_id requirement won't fly as userspace expects to be able to stuff virtual toplogy info into the APIC ID.
