linux-kernel - Re: [PATCH v4 26/32] KVM: SVM: Always update local APIC on writes to logical dest register

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Message-ID: <0f403e5a9d9758dac90e6a1e3cda1a95e693cad8.camel@redhat.com>
Date:   Thu, 08 Dec 2022 23:58:43 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alejandro Jimenez <alejandro.j.jimenez@...cle.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Li RongQing <lirongqing@...du.com>
Subject: Re: [PATCH v4 26/32] KVM: SVM: Always update local APIC on writes
 to logical dest register

On Sat, 2022-10-01 at 00:59 +0000, Sean Christopherson wrote:
> Update the vCPU's local (virtual) APIC on LDR writes even if the write
> "fails".  The APIC needs to recalc the optimized logical map even if the
> LDR is invalid or zero, e.g. if the guest clears its LDR, the optimized
> map will be left as is and the vCPU will receive interrupts using its
> old LDR.
> 
> Fixes: 18f40c53e10f ("svm: Add VMEXIT handlers for AVIC")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/svm/avic.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 27d5abc15a91..2b640c73f447 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -573,7 +573,7 @@ static void avic_invalidate_logical_id_entry(struct kvm_vcpu *vcpu)
>  		clear_bit(AVIC_LOGICAL_ID_ENTRY_VALID_BIT, (unsigned long *)entry);
>  }
>  
> -static int avic_handle_ldr_update(struct kvm_vcpu *vcpu)
> +static void avic_handle_ldr_update(struct kvm_vcpu *vcpu)
>  {
>  	int ret = 0;
>  	struct vcpu_svm *svm = to_svm(vcpu);
> @@ -582,10 +582,10 @@ static int avic_handle_ldr_update(struct kvm_vcpu *vcpu)
>  
>  	/* AVIC does not support LDR update for x2APIC */
>  	if (apic_x2apic_mode(vcpu->arch.apic))
> -		return 0;
> +		return;
>  
>  	if (ldr == svm->ldr_reg)
> -		return 0;
> +		return;
>  
>  	avic_invalidate_logical_id_entry(vcpu);
>  
> @@ -594,8 +594,6 @@ static int avic_handle_ldr_update(struct kvm_vcpu *vcpu)
>  
>  	if (!ret)
>  		svm->ldr_reg = ldr;
> -
> -	return ret;
>  }
>  
>  static void avic_handle_dfr_update(struct kvm_vcpu *vcpu)
> @@ -617,8 +615,7 @@ static int avic_unaccel_trap_write(struct kvm_vcpu *vcpu)
>  
>  	switch (offset) {
>  	case APIC_LDR:
> -		if (avic_handle_ldr_update(vcpu))
> -			return 0;
> +		avic_handle_ldr_update(vcpu);
>  		break;
>  	case APIC_DFR:
>  		avic_handle_dfr_update(vcpu);


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

Best regards,
	Maxim Levitsky