Re: [Qemu-devel] [PATCH] target-i386: add pcid to both Sandy Bridge and Ivy Bridge

[Eduardo Habkost]

On Mon, Jan 08, 2018 at 11:22:36PM +0100, Vincent Bernat wrote:
>  ❦  8 janvier 2018 20:14 -0200, Eduardo Habkost <address@hidden> :
> 
> >> 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