linux-kernel - Re: [PATCH v2 14/21] KVM: x86: Use kvm_queue_exception

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Date:   Wed, 06 Jul 2022 15:04:45 +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, Oliver Upton <oupton@...gle.com>,
        Peter Shier <pshier@...gle.com>
Subject: Re: [PATCH v2 14/21] KVM: x86: Use kvm_queue_exception_e() to queue
 #DF

On Tue, 2022-06-14 at 20:47 +0000, Sean Christopherson wrote:
> Queue #DF by recursing on kvm_multiple_exception() by way of
> kvm_queue_exception_e() instead of open coding the behavior.  This will
> allow KVM to Just Work when a future commit moves exception interception
> checks (for L2 => L1) into kvm_multiple_exception().

Typo: You mean Just Work (tm) ;-) 

> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/x86.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 511c0c8af80e..e45465075005 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -663,25 +663,22 @@ static void kvm_multiple_exception(struct kvm_vcpu *vcpu,
>  	}
>  	class1 = exception_class(prev_nr);
>  	class2 = exception_class(nr);
> -	if ((class1 == EXCPT_CONTRIBUTORY && class2 == EXCPT_CONTRIBUTORY)
> -		|| (class1 == EXCPT_PF && class2 != EXCPT_BENIGN)) {
> +	if ((class1 == EXCPT_CONTRIBUTORY && class2 == EXCPT_CONTRIBUTORY) ||
> +	    (class1 == EXCPT_PF && class2 != EXCPT_BENIGN)) {
>  		/*
> -		 * Generate double fault per SDM Table 5-5.  Set
> -		 * exception.pending = true so that the double fault
> -		 * can trigger a nested vmexit.
> +		 * Synthesize #DF.  Clear the previously injected or pending
> +		 * exception so as not to incorrectly trigger shutdown.
>  		 */
> -		vcpu->arch.exception.pending = true;
>  		vcpu->arch.exception.injected = false;
> -		vcpu->arch.exception.has_error_code = true;
> -		vcpu->arch.exception.vector = DF_VECTOR;
> -		vcpu->arch.exception.error_code = 0;
> -		vcpu->arch.exception.has_payload = false;
> -		vcpu->arch.exception.payload = 0;
> -	} else
> +		vcpu->arch.exception.pending = false;
> +
> +		kvm_queue_exception_e(vcpu, DF_VECTOR, 0);
> +	} else {
>  		/* replace previous exception with a new one in a hope
>  		   that instruction re-execution will regenerate lost
>  		   exception */
>  		goto queue;
> +	}
>  }
>  
>  void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr)

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

Best regards,
	Maxim Levitsky