linux-kernel - Re: [PATCH v3 13/62] KVM: SVM: Drop redundant check in AVIC code on ID during vCPU creation

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Message-ID: <qusmkqqsvc7hyuemddv66mooach7mdq66mxbk7qbr6if6spguj@k57k5lqmvt5u>
Date: Tue, 17 Jun 2025 20:19:00 +0530
From: Naveen N Rao <naveen@...nel.org>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Paolo Bonzini <pbonzini@...hat.com>, Joerg Roedel <joro@...tes.org>, 
	David Woodhouse <dwmw2@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, kvm@...r.kernel.org, 
	iommu@...ts.linux.dev, linux-kernel@...r.kernel.org, Sairaj Kodilkar <sarunkod@....com>, 
	Vasant Hegde <vasant.hegde@....com>, Maxim Levitsky <mlevitsk@...hat.com>, 
	Joao Martins <joao.m.martins@...cle.com>, Francesco Lavra <francescolavra.fl@...il.com>, 
	David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH v3 13/62] KVM: SVM: Drop redundant check in AVIC code on
 ID during vCPU creation

On Wed, Jun 11, 2025 at 03:45:16PM -0700, Sean Christopherson wrote:
>  static int avic_init_backing_page(struct kvm_vcpu *vcpu)
>  {
> -	u64 *entry, new_entry;
> -	int id = vcpu->vcpu_id;
> +	struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);
>  	struct vcpu_svm *svm = to_svm(vcpu);
> +	u32 id = vcpu->vcpu_id;
> +	u64 *table, new_entry;
>  
>  	/*
>  	 * Inhibit AVIC if the vCPU ID is bigger than what is supported by AVIC
> @@ -291,6 +277,9 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu)
>  		return 0;
>  	}
>  
> +	BUILD_BUG_ON((AVIC_MAX_PHYSICAL_ID + 1) * sizeof(*table) > PAGE_SIZE ||
> +		     (X2AVIC_MAX_PHYSICAL_ID + 1) * sizeof(*table) > PAGE_SIZE);
						    ^^^^^^^^^^^^^^
Renaming new_entry to just 'entry' and using sizeof(entry) makes this 
more readable for me. Otherwise, for this patch:
Reviewed-by: Naveen N Rao (AMD) <naveen@...nel.org>


As an aside, there are a few static asserts to validate some of the 
related macros. Can this also be a static_assert(), or is there is 
reason to prefer BUILD_BUG_ON()?


- Naveen