linux-kernel - Re: [PATCH v4 13/15] KVM: x86: Warning APICv inconsistency only when vcpu APIC mode is valid

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Date:   Mon, 9 May 2022 15:38:40 +0200
From:   "Gupta, Pankaj" <pankaj.gupta@....com>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     pbonzini@...hat.com, mlevitsk@...hat.com, seanjc@...gle.com,
        joro@...tes.org, jon.grimm@....com, wei.huang2@....com,
        terry.bowman@....com
Subject: Re: [PATCH v4 13/15] KVM: x86: Warning APICv inconsistency only when
 vcpu APIC mode is valid


> When launching a VM with x2APIC and specify more than 255 vCPUs,
> the guest kernel can disable x2APIC (e.g. specify nox2apic kernel option).
> The VM fallbacks to xAPIC mode, and disable the vCPU ID 255 and greater.
> 
> In this case, APICV is deactivated for the disabled vCPUs.
> However, the current APICv consistency warning does not account for
> this case, which results in a warning.
> 
> Therefore, modify warning logic to report only when vCPU APIC mode
> is valid.
> 
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>   arch/x86/kvm/x86.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 77e49892dea1..0febaca80feb 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10242,7 +10242,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>   		 * per-VM state, and responsing vCPUs must wait for the update
>   		 * to complete before servicing KVM_REQ_APICV_UPDATE.
>   		 */
> -		WARN_ON_ONCE(kvm_vcpu_apicv_activated(vcpu) != kvm_vcpu_apicv_active(vcpu));
> +		WARN_ON_ONCE((kvm_vcpu_apicv_activated(vcpu) != kvm_vcpu_apicv_active(vcpu)) &&
> +			     (kvm_get_apic_mode(vcpu) != LAPIC_MODE_DISABLED));
>   
>   		exit_fastpath = static_call(kvm_x86_vcpu_run)(vcpu);
>   		if (likely(exit_fastpath != EXIT_FASTPATH_REENTER_GUEST))
Looks good to me.
Reviewed-by: Pankaj Gupta <pankaj.gupta@....com>