Re: [Qemu-devel] [PATCH v2 0/3] i386: Add "max" CPU model to TCG and KVM

[Eduardo Habkost]

On Fri, Feb 24, 2017 at 01:48:46PM +0000, Peter Maydell wrote:
> On 22 February 2017 at 18:39, Eduardo Habkost <address@hidden> wrote:
> > Changes v1 -> v2:
> > * Fix build without CONFIG_KVM at lmce_supported()
> > * Rebased on top of my x86-next branch:
> >   https://github.com/ehabkost/qemu x86-next
> >
> > Git branch for testing:
> >   https://github.com/ehabkost/qemu-hacks work/x86-cpu-max-tcg
> >
> > libvirt code to use the new feature already exist, and were
> > submitted to libvir-list, at:
> >   https://www.mail-archive.com/address@hidden/msg142168.html
> >
> > ---
> >
> > This is a replacement for the previous series that enabled the
> > "host" CPU model on TCG. Now a new "max" CPU is being added,
> > while keeping "host" KVM-specific.
> >
> > In addition to simply adding "max" as a copy of the existing
> > "host" CPU model, additional patches change it to not use any
> > host CPUID information when in TCG mode.
> 
> 
> I had a look at implementing this for ARM, and ran into problems
> because of how we've done '-cpu host'. For us the "host" CPU
> type is registered dynamically when kvm_init() is called,
> because (a) it only exists if -enable-kvm and (b) it probes
> the kernel to find out what's available. So I could easily
> add 'max' in the same place; but then where should I add the
> type definition of 'max' for the non-KVM case?

I recommend registering the type unconditionally, moving
KVM-specific initialization to ->instance_init() and/or
->realize() (being careful to make instance_init() not crash if
KVM is disabled), and make ->realize() fail if KVM is disabled.
IIRC, we did exactly that on x86 a while ago.

-- 
Eduardo