Messages in this thread | | | Date | Mon, 13 Dec 2021 12:34:32 +0100 | Subject | Re: [PATCH v2 1/5] KVM: nSVM: deal with L1 hypervisor that intercepts interrupts but lets L2 control EFLAGS.IF | From | Paolo Bonzini <> |
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On 12/13/21 11:46, Maxim Levitsky wrote: > Fix a corner case in which L1 hypervisor intercepts interrupts (INTERCEPT_INTR) > and either doesn't use virtual interrupt masking (V_INTR_MASKING) or > enters a nested guest with EFLAGS.IF disabled prior to the entry. > > In this case, despite the fact that L1 intercepts the interrupts, > KVM still needs to set up an interrupt window to wait before it > can deliver INTR vmexit. > > Currently instead, the KVM enters an endless loop of 'req_immediate_exit'. > > Note that on VMX this case is impossible as there is only > 'vmexit on external interrupts' execution control which either set, > in which case both host and guest's EFLAGS.IF > is ignored, or clear, in which case no VMexit is delivered. > > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com> > --- > arch/x86/kvm/svm/svm.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index e57e6857e0630..c9668a3b51011 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -3372,17 +3372,21 @@ bool svm_interrupt_blocked(struct kvm_vcpu *vcpu) > static int svm_interrupt_allowed(struct kvm_vcpu *vcpu, bool for_injection) > { > struct vcpu_svm *svm = to_svm(vcpu); > + bool blocked; > + > if (svm->nested.nested_run_pending) > return -EBUSY; > > + blocked = svm_interrupt_blocked(vcpu); > + > /* > * An IRQ must not be injected into L2 if it's supposed to VM-Exit, > * e.g. if the IRQ arrived asynchronously after checking nested events. > */ > if (for_injection && is_guest_mode(vcpu) && nested_exit_on_intr(svm)) > - return -EBUSY; > - > - return !svm_interrupt_blocked(vcpu); > + return !blocked ? -EBUSY : 0; > + else > + return !blocked; > } > > static void svm_enable_irq_window(struct kvm_vcpu *vcpu) >
Right, another case is when CLGI is not trapped and the guest therefore runs with GIF=0. I think that means that a similar change has to be done in all the *_allowed functions.
I would write it as
if (svm->nested.nested_run_pending) return -EBUSY; if (svm_interrupt_blocked(vcpu)) return 0;
/* * An IRQ must not be injected into L2 if it's supposed to VM-Exit, * e.g. if the IRQ arrived asynchronously after checking nested events. */ if (for_injection && is_guest_mode(vcpu) && nested_exit_on_intr(svm)) return -EBUSY; return 1;
Paolo
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