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

Alexander Graf
2010-04-23T13:46:14Z

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?

Alex