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

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Message-ID: <20220910013935.GA699006@ls.amr.corp.intel.com>
Date:   Fri, 9 Sep 2022 18:39:35 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     "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>,
        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

On Fri, Sep 09, 2022 at 05:55:14AM +0000,
Christophe Leroy <christophe.leroy@...roup.eu> wrote:

> 
> 
> 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.

Ok, will move the comment into the commit message.
-- 
Isaku Yamahata <isaku.yamahata@...il.com>