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

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Date:   Mon, 26 Sep 2022 17:40:54 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     isaku.yamahata@...el.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        isaku.yamahata@...il.com, Kai Huang <kai.huang@...el.com>,
        Chao Gao <chao.gao@...el.com>,
        Atish Patra <atishp@...shpatra.org>,
        Shaokun Zhang <zhangshaokun@...ilicon.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Huang Ying <ying.huang@...el.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>, linuxppc-dev@...ts.ozlabs.org,
        Fabiano Rosas <farosas@...ux.ibm.com>
Subject: Re: [PATCH v5 27/30] RFC: KVM: powerpc: Move processor compatibility
 check to hardware setup

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

> isaku.yamahata@...el.com writes:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> >
> > 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@...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 | 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@...erman.id.au> (powerpc)

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