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

Alexander Graf
2010-04-23T14:19:46Z

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@amd.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?
>
> 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