linux-kernel - Re: [PATCH v4 23/26] RFC: KVM: powerpc: Move processor compatibility check to hardware setup

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Date:   Fri, 9 Sep 2022 05:55:14 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "isaku.yamahata@...el.com" <isaku.yamahata@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        Yuan Yao <yuan.yao@...ux.intel.com>
CC:     Huang Ying <ying.huang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Fabiano Rosas <farosas@...ux.ibm.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        John Garry <john.garry@...wei.com>,
        Shaokun Zhang <zhangshaokun@...ilicon.com>,
        Kai Huang <kai.huang@...el.com>,
        Atish Patra <atishp@...shpatra.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Qi Liu <liuqi115@...wei.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        Chao Gao <chao.gao@...el.com>
Subject: Re: [PATCH v4 23/26] RFC: KVM: powerpc: Move processor compatibility
 check to hardware setup



Le 09/09/2022 à 01:25, isaku.yamahata@...el.com a écrit :
> [Vous ne recevez pas souvent de courriers de isaku.yamahata@...el.com. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> 
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Move processor compatibility check from kvm_arch_processor_compat() into
> 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.
> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: Fabiano Rosas <farosas@...ux.ibm.com>
> ---
>   arch/powerpc/kvm/powerpc.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 7b56d6ccfdfb..7e3a6659f107 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -444,12 +444,21 @@ int kvm_arch_hardware_enable(void)
> 
>   int kvm_arch_hardware_setup(void *opaque)
>   {
> -       return 0;
> +       /*
> +        * kvmppc_core_check_processor_compat() checks the global variable.
> +        * No point to check on all processors or at runtime.
> +        * 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")
> +        */

This explanation shouldn't be in the code. The content of other file may 
change in the future, the files may be renamed or deleted, new files may 
be added. And there is no added value with that comment.

That detailed explanation should go in the commit message.

> +       return kvmppc_core_check_processor_compat();
>   }
> 
>   int kvm_arch_check_processor_compat(void)
>   {
> -       return kvmppc_core_check_processor_compat();
> +       return 0;
>   }
> 
>   int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> --
> 2.25.1
>