Re: [PATCH v5 27/30] RFC: KVM: powerpc: Move processor compatibility check to hardware setup

[Isaku Yamahata]

On Fri, Sep 23, 2022 at 04:58:41PM +1000,
Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:

> isaku.yamahata@xxxxxxxxx writes:
> > From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> >
> > Move processor compatibility check from kvm_arch_processor_compat() into
>                                           ^ 
>                                           kvm_arch_check_processor_compat()
> 
> > kvm_arch_hardware_setup().  The check does model name comparison with a
> > global variable, cur_cpu_spec.  There is no point to check it at run time
> > on all processors.
> 
> A key detail I had to look up is that both kvm_arch_hardware_setup() and
> kvm_arch_check_processor_compat() are called from kvm_init(), one after
> the other. But the latter is called on each CPU.
> 
> And because the powerpc implementation of kvm_arch_check_processor_compat()
> just checks a global, there's no need to call it on every CPU.
> 
> > kvmppc_core_check_processor_compat() checks the global variable.  There are
> > five implementation for it as follows.
> 
> There are three implementations not five.

Thanks. I'll update the commit message.

> >   arch/powerpc/include/asm/cputable.h: extern struct cpu_spec *cur_cpu_spec;
> >   arch/powerpc/kvm/book3s.c: return 0
> >   arch/powerpc/kvm/e500.c: strcmp(cur_cpu_spec->cpu_name, "e500v2")
> >   arch/powerpc/kvm/e500mc.c: strcmp(cur_cpu_spec->cpu_name, "e500mc")
> >                              strcmp(cur_cpu_spec->cpu_name, "e5500")
> >                              strcmp(cur_cpu_spec->cpu_name, "e6500")
> >
> > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> > Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> > Cc: Fabiano Rosas <farosas@xxxxxxxxxxxxx>
> > ---
> >  arch/powerpc/kvm/powerpc.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> > index 7b56d6ccfdfb..31dc4f231e9d 100644
> > --- a/arch/powerpc/kvm/powerpc.c
> > +++ b/arch/powerpc/kvm/powerpc.c
> > @@ -444,12 +444,12 @@ int kvm_arch_hardware_enable(void)
> >  
> >  int kvm_arch_hardware_setup(void *opaque)
> >  {
> > -	return 0;
> > +	return kvmppc_core_check_processor_compat();
> >  }
> >  
> >  int kvm_arch_check_processor_compat(void)
> >  {
> > -	return kvmppc_core_check_processor_compat();
> > +	return 0;
> >  }
> 
> The actual change seems OK. I gave it a quick test boot and ran some
> VMs, everything seems to work as before.
> 
> Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> (powerpc)

Thanks so much for testing. I'll remove RFC.
-- 
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>