Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Michael Ellerman <mpe@ellerman.id.au>
To:     isaku.yamahata@intel.com, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>
Cc:     isaku.yamahata@intel.com, isaku.yamahata@gmail.com,
        Kai Huang <kai.huang@intel.com>, Chao Gao <chao.gao@intel.com>,
        Atish Patra <atishp@atishpatra.org>,
        Shaokun Zhang <zhangshaokun@hisilicon.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Huang Ying <ying.huang@intel.com>,
        Huacai Chen <chenhuacai@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Borislav Petkov <bp@alien8.de>, linuxppc-dev@lists.ozlabs.org,
        Fabiano Rosas <farosas@linux.ibm.com>
Subject: Re: [PATCH v5 27/30] RFC: KVM: powerpc: Move processor
 compatibility check to hardware setup
In-Reply-To: <574ca90fdaec0f37c197d9600d47d48a74f324bd.1663869838.git.isaku.yamahata@intel.com>
References: <cover.1663869838.git.isaku.yamahata@intel.com>
 <574ca90fdaec0f37c197d9600d47d48a74f324bd.1663869838.git.isaku.yamahata@intel.com>
Date:   Fri, 23 Sep 2022 16:58:41 +1000
Message-ID: <8735ci1sri.fsf@mpe.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

isaku.yamahata@intel.com writes:
> From: Isaku Yamahata <isaku.yamahata@intel.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.

>   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@google.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: Fabiano Rosas <farosas@linux.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@ellerman.id.au> (powerpc)

cheers