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

[Alexander Graf]

On 23.04.2010, at 16:13, Joerg Roedel wrote:

> On Fri, Apr 23, 2010 at 03:46:07PM +0200, Alexander Graf wrote:
>> 
>> 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@xxxxxxx>
>>> ---
>>> 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?
> 
> Why not? We can't inject an NMI directly into L2 if the nested
> hypervisor intercepts it.

So where did the code go that does the #vmexit in case the nested hypervisor does intercept it? It used to be nested_svm_nmi(), right?


Alex

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