linux-kernel - Re: [PATCH 1/8] KVM: SVM: Fix nested nmi handling

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Date:	Fri, 23 Apr 2010 15:46:07 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] KVM: SVM: Fix nested nmi handling


On 22.04.2010, at 12:33, Joerg Roedel wrote:

> The patch introducing nested nmi handling had a bug. The
> check does not belong to enable_nmi_window but must be in
> nmi_allowed. This patch fixes this.
> 
> Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> ---
> arch/x86/kvm/svm.c |   16 +++++++++-------
> 1 files changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index ab78eb8..ec20584 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -2771,8 +2771,12 @@ static int svm_nmi_allowed(struct kvm_vcpu *vcpu)
> {
> 	struct vcpu_svm *svm = to_svm(vcpu);
> 	struct vmcb *vmcb = svm->vmcb;
> -	return !(vmcb->control.int_state & SVM_INTERRUPT_SHADOW_MASK) &&
> -		!(svm->vcpu.arch.hflags & HF_NMI_MASK);
> +	int ret;
> +	ret = !(vmcb->control.int_state & SVM_INTERRUPT_SHADOW_MASK) &&
> +	      !(svm->vcpu.arch.hflags & HF_NMI_MASK);
> +	ret = ret && gif_set(svm) && nested_svm_nmi(svm);
> +
> +	return ret;
> }
> 
> static bool svm_get_nmi_mask(struct kvm_vcpu *vcpu)
> @@ -2841,11 +2845,9 @@ static void enable_nmi_window(struct kvm_vcpu *vcpu)
> 	 * Something prevents NMI from been injected. Single step over possible
> 	 * problem (IRET or exception injection or interrupt shadow)
> 	 */
> -	if (gif_set(svm) && nested_svm_nmi(svm)) {
> -		svm->nmi_singlestep = true;
> -		svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
> -		update_db_intercept(vcpu);
> -	}
> +	svm->nmi_singlestep = true;
> +	svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
> +	update_db_intercept(vcpu);

So we're always messing with the nested guest state when the host wants to inject an nmi into the l1 guest? Is that safe?


Alex

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