On 01/07/2016 17:06, Paolo Bonzini wrote: >>> >> > Should it? >> Yes, x2APIC ID cannot be changed in hardware and is initialized to the >> intitial APIC ID. >> Letting LAPIC_SET change x2APIC ID would allow scenarios where userspace >> reuses old VMs instead of building new ones after reconfiguration. >> I don't think it's a sensible use case and it it is currently broken, >> because we don't exit to userspace when changing APIC mode, so KVM would >> just set APIC ID to VCPU ID on any transition and userspace couldn't >> amend it. Forgot to reply about this: letting SET_LAPIC change x2APIC IDs is nonsense. In x2APIC mode + new capability disabled SET_LAPIC should ignore the id register altogether for backwards compatibility. In x2APIC mode + new capability enabled it should either ignore it, or fail if the x2APIC ID doesn't match the VCPU id. I suspect the latter is better because it would help catching the case where userspace is erroneously shifting the id left to bits 31-24. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
