linux-kernel - Re: [RFC PATCH 01/13] KVM: SVM: Add warning when encounter invalid APIC ID

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Message-ID: <c9e8ca945fc08f502701c4df7c9fffa1f5f0c001.camel@redhat.com>
Date:   Thu, 24 Feb 2022 18:30:30 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     pbonzini@...hat.com, seanjc@...gle.com, joro@...tes.org,
        jon.grimm@....com, wei.huang2@....com, terry.bowman@....com
Subject: Re: [RFC PATCH 01/13] KVM: SVM: Add warning when encounter invalid
 APIC ID

On Sun, 2022-02-20 at 20:19 -0600, Suravee Suthikulpanit wrote:
> Current logic checks if avic_get_physical_id_entry() fails to
> get the entry, and return error. This could silently cause
> AVIC to fail to operate.  Therefore, add WARN_ON to help
> report this error.
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>  arch/x86/kvm/svm/avic.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index f07956f15d3b..472445aaaf42 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -447,8 +447,10 @@ static int avic_handle_apic_id_update(struct kvm_vcpu *vcpu)
>  
>  	old = avic_get_physical_id_entry(vcpu, vcpu->vcpu_id);
>  	new = avic_get_physical_id_entry(vcpu, id);
> -	if (!new || !old)
> +	if (!new || !old) {
> +		WARN_ON(1);
>  		return 1;
> +	}
>  
>  	/* We need to move physical_id_entry to new offset */
>  	*new = *old;

I about to purge all of this code, and disallow setting the apicid regardles
if x2apic, or plain xapic was used at least when AVIC is enabled.
I really hope for this to be accepted, so we won't need to fix this code.

Best regards,
	Maxim Levitsky