linux-kernel - Re: [PATCH 2/2] KVM: SVM: Extend host physical APIC ID field to support more than 8-bit

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Date:   Wed, 10 Nov 2021 19:48:21 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org,
        pbonzini@...hat.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, peterz@...radead.org,
        hpa@...or.com, thomas.lendacky@....com, jon.grimm@....com
Subject: Re: [PATCH 2/2] KVM: SVM: Extend host physical APIC ID field to
 support more than 8-bit

On Wed, Nov 10, 2021, Suravee Suthikulpanit wrote:
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 989685098b3e..0b066bb5149d 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1031,6 +1031,12 @@ static __init int svm_hardware_setup(void)
>  			nrips = false;
>  	}
>  
> +	if (avic) {
> +		r = avic_init_host_physical_apicid_mask();
> +		if (r)
> +			avic = false;
> +	}

Haven't yet dedicated any brain cells to the rest of the patch, but this can be
written as

	if (avic && avic_init_host_physical_apicid_mask())
		avic = false;

or 

	avic = avic && !avic_init_host_physical_apicid_mask();

But looking at the context below, combining everything would be preferable.  I
would say split out the enable_apicv part to make it more obvious that enable_apicv
is merely a reflection of avic.

	avic = avic && npt_enabled && boot_cpu_has(X86_FEATURE_AVIC) &&
	       !avic_init_host_physical_apicid_mask();
	enable_apicv = avic;

> +
>  	enable_apicv = avic = avic && npt_enabled && boot_cpu_has(X86_FEATURE_AVIC);
>  
>  	if (enable_apicv) {