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

[Michael Ellerman]

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.

>   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)

cheers