Re: [Qemu-devel] [PATCH] spapr: move registration of "host" CPU core type to machine code

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 27 Sep 2017 16:21:43 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Tue, Sep 26, 2017 at 09:19:28AM +0200, Greg Kurz wrote:
> > On Tue, 26 Sep 2017 12:57:39 +1000
> > David Gibson <david@gibson.dropbear.id.au> wrote:
> >   
> > > On Mon, Sep 25, 2017 at 11:47:33AM +0200, Greg Kurz wrote:  
> > > > The CPU core abstraction belongs to the machine code. This also gets
> > > > rid of some code duplication.
> > > > 
> > > > Signed-off-by: Greg Kurz <groug@kaod.org>
> > > > ---
> > > > 
> > > > hw/ppc/spapr_cpu_core.h is also included elsewhere in target/ppc/kvm.c
> > > > but this is already handled by the following cleanup patch:    
> > > 
> > > I don't really see what the advantage of this is.  As others have
> > > pointed out it leads to the host type being registered very late,
> > > which could cause problems.
> > >   
> > 
> > Well, the goal was to consolidate the code to register sPAPRCPUCore types in
> > the spapr code, instead of open-coding it in spapr_cpu_core.c and kvm.c... 
> > 
> > But now I realize that delaying the registration even more is a bad idea. And,
> > the other way round, registering a static type earlier as asked by Igor would
> > require all parent types to be already registered, which seems to be impossible
> > to guarantee with the current code.
> > 
> > Maybe we could at least have kvm_ppc_register_host_cpu_type() to call a
> > function in spapr_cpu_core.c instead of duplicating the registration
> > code ?  
> 
> I think that sounds like a better idea.  It's still a little bodgy
> with the abstraction boundaries, but I think that's unavoidable: this
> fundamentally depends on both KVM's presence and use of the PAPR
> machine type.  Whichever place we put it, you could argue it belongs
> better in the other one.
it looks like kvm_ppc_register_host_cpu_type() doesn't depend on
anything that requires KVM being present/initialized, so I'd
suggest to:

  - 1: revert commit 715d4b96 and do alias hiding another way
  - 2: move host core type registration into spapr_cpu_core.c and make it static like x86
  - 3: move host cpu type into target/ppc/translate_init.c where the rest
       of cpu types is initialized and make it static like x86