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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 23 Sep 2022 16:58:41 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     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>
Cc:     isaku.yamahata@...el.com, 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

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.

>   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)

cheers