linux-kernel - Re: [PATCH v2 5/7] KVM: x86: Move .pmu_ops to kvm_x86_init_ops and tagged as _

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Date:   Wed, 8 Dec 2021 18:17:15 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/7] KVM: x86: Move .pmu_ops to kvm_x86_init_ops and
 tagged as __initdata

s/tagged/tag

On Mon, Nov 08, 2021, Like Xu wrote:
> From: Like Xu <likexu@...cent.com>
> 
> The pmu_ops should be moved to kvm_x86_init_ops and tagged as __initdata.

State what the patch does, not what "should" be done.

  Now that pmu_ops is copied by value during kvm_arch_hardware_setup(), move
  the pointer to kvm_x86_init_ops and tag implementations as __initdata to make
  the implementations unreachable once KVM is loaded, e.g. to make it harder to
  sneak in post-init modification bugs.

> That'll save those precious few bytes, and more importantly make
> the original ops unreachable, i.e. make it harder to sneak in post-init
> modification bugs.
> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Like Xu <likexu@...cent.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 4 ++--
>  arch/x86/kvm/svm/pmu.c          | 2 +-
>  arch/x86/kvm/svm/svm.c          | 2 +-
>  arch/x86/kvm/vmx/pmu_intel.c    | 2 +-
>  arch/x86/kvm/vmx/vmx.c          | 2 +-
>  arch/x86/kvm/x86.c              | 2 +-
>  6 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index c2d4ee2973c5..00760a3ac88c 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1436,8 +1436,7 @@ struct kvm_x86_ops {
>  	int cpu_dirty_log_size;
>  	void (*update_cpu_dirty_logging)(struct kvm_vcpu *vcpu);
>  
> -	/* pmu operations of sub-arch */
> -	const struct kvm_pmu_ops *pmu_ops;
> +	/* nested operations of sub-arch */

No need for the new comment.

>  	const struct kvm_x86_nested_ops *nested_ops;
>  
>  	/*

Nits aside,

Reviewed-by: Sean Christopherson <seanjc@...gle.com>

I'd also be a-ok squashing this with the copy-by-value patch.