linux-kernel - Re: [PATCH 1/4] KVM: x86: Tag APICv DISABLE inhibit, not ABSENT, if APICv is disabled

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Message-ID: <d2820bafeea6e908108bac863269a7ff7f519999.camel@redhat.com>
Date:   Mon, 18 Apr 2022 11:37:48 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Gaoning Pan <pgn@....edu.cn>,
        Yongkang Jia <kangel@....edu.cn>
Subject: Re: [PATCH 1/4] KVM: x86: Tag APICv DISABLE inhibit, not ABSENT, if
 APICv is disabled

On Sat, 2022-04-16 at 03:42 +0000, Sean Christopherson wrote:
> Set the DISABLE inhibit, not the ABSENT inhibit, if APICv is disabled via
> module param.  A recent refactoring to add a wrapper for setting/clearing
> inhibits unintentionally changed the flag, probably due to a copy+paste
> goof.
> 
> Fixes: 4f4c4a3ee53c ("KVM: x86: Trace all APICv inhibit changes and capture overall status")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/x86.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ab336f7c82e4..753296902535 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9159,7 +9159,7 @@ static void kvm_apicv_init(struct kvm *kvm)
>  
>  	if (!enable_apicv)
>  		set_or_clear_apicv_inhibit(inhibits,
> -					   APICV_INHIBIT_REASON_ABSENT, true);
> +					   APICV_INHIBIT_REASON_DISABLE, true);
>  }
>  
>  static void kvm_sched_yield(struct kvm_vcpu *vcpu, unsigned long dest_id)

So ABSENT means that userspace didn't enable, it and DISABLE means kernel module param disabled it.
I didn't follow patches that touched those but it feels like we can use a single inhibit reason for both,
or at least make better names for this. APICV_INHIBIT_REASON_ABSENT doesn't sound good to me.

Having said that, the patch is OK.

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky