On Mon, Jan 08, 2018 at 11:22:36PM +0100, Vincent Bernat wrote: > ❦ 8 janvier 2018 20:14 -0200, Eduardo Habkost <ehabk...@redhat.com> : > > >> What are the consequences of running a too old kernel? Would KVM just > >> hide PCID flag? > > > > On an old kernel, the SandyBridge and IvyBridge CPU models will > > be unexpectedly become not runnable. > > But, isn't it the same for more recent models that already have PCID > enabled?
Yes, the more recent models are already not runnable on those hosts. The key here is "unexpectedly": management software can assume that the CPU model won't become unrunnable when it was runnable in the past, and logic that decides if/where a VM can be started (or migrated to) might break. -- Eduardo
