| Message ID | 20221129193717.513824-4-mlevitsk@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | SVM: vNMI (with my fixes) | expand |
Shortlog is too long, maybe this? KVM: nSVM: Raise event on nested VM exit if L1 doesn't intercept IRQs On Tue, Nov 29, 2022, Maxim Levitsky wrote: > If the L2 doesn't intercept interrupts, then the KVM will use vmcb02's s/the L2/L2, though don't you mean L1? > V_IRQ for L1 (to detect the interrupt window) "an interrupt window", i.e. there's not just one window. > In this case on the nested VM exit KVM might need to copy the V_IRQ bit s/the nested/nested > from the vmcb02 to the vmcb01, to continue waiting for the > interrupt window. > > To make it simple, just raise the KVM_REQ_EVENT request, which > execution will lead to the reenabling of the interrupt > window if needed. > > Note that this is a theoretical bug because the KVM already does raise s/the KVM/KVM > the KVM_REQ_EVENT request one each nested VM exit because the nested s/the KVM_REQ_EVENT/KVM_REQ_EVENT, and s/one/on > VM exit resets RFLAGS and the kvm_set_rflags() raises the > KVM_REQ_EVENT request in the response. > > However raising this request explicitly, together with > documenting why this is needed, is still preferred. > > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com> > --- > arch/x86/kvm/svm/nested.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c > index aad3145b2f62fe..e891318595113e 100644 > --- a/arch/x86/kvm/svm/nested.c > +++ b/arch/x86/kvm/svm/nested.c > @@ -1016,6 +1016,31 @@ int nested_svm_vmexit(struct vcpu_svm *svm) > > svm_switch_vmcb(svm, &svm->vmcb01); > > + /* Note about synchronizing some of int_ctl bits from vmcb02 to vmcb01: /* * Preferred block comment style... > + * > + * - V_IRQ, V_IRQ_VECTOR, V_INTR_PRIO_MASK, V_IGN_TPR: Drop the "-" to be consistent with the rest of the paragraphs. > + * If the L2 doesn't intercept interrupts, then > + * (even if the L2 does use virtual interrupt masking), KVM uses "L2" to refer to the thing running at L2. I think what you are referring to here is vmcb12? And that's controlled by L1. > + * KVM will use the vmcb02's V_INTR to detect interrupt window. s/the vmcb02/vmcb02 Which of the V_INTR fields does this refer to? Oooh, you're saying the KVM injects a virtual interrupt into L2 using vmcb02 in order to determine when L2 has IRQs enabled. Why does KVM do that? Why not pend the actual IRQ directly? > + * > + * In this case, the KVM raises the KVM_REQ_EVENT to ensure that interrupt window s/the KVM_REQ_EVENT/KVM_REQ_EVENT > + * is not lost and this implicitly copies these bits from vmcb02 to vmcb01 Too many pronouns. What do "this" and "these bits" refer to? > + * > + * V_TPR: > + * If the L2 doesn't use virtual interrupt masking, then the L1's vTPR > + * is stored in the vmcb02 but its value doesn't need to be copied from/to > + * vmcb01 because it is copied from/to the TPR APIC's register on > + * each VM entry/exit. > + * > + * V_GIF: > + * - If the nested vGIF is not used, KVM uses vmcb02's V_GIF for L1's V_GIF, Drop this "-" too. > + * however, the L1 vGIF is reset to false on each VM exit, thus > + * there is no need to copy it from vmcb02 to vmcb01. > + */ > + > + if (!nested_exit_on_intr(svm)) > + kvm_make_request(KVM_REQ_EVENT, &svm->vcpu); > + > if (unlikely(svm->lbrv_enabled && (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) { > svm_copy_lbrs(vmcb12, vmcb02); > svm_update_lbrv(vcpu); > -- > 2.26.3 >
On Sat, Jan 28, 2023, Sean Christopherson wrote: > > + * If the L2 doesn't intercept interrupts, then > > + * (even if the L2 does use virtual interrupt masking), > > KVM uses "L2" to refer to the thing running at L2. I think what you are referring > to here is vmcb12? And that's controlled by L1. > > > + * KVM will use the vmcb02's V_INTR to detect interrupt window. > > s/the vmcb02/vmcb02 > > Which of the V_INTR fields does this refer to? Oooh, you're saying the KVM injects > a virtual interrupt into L2 using vmcb02 in order to determine when L2 has IRQs > enabled. > > Why does KVM do that? Why not pend the actual IRQ directly? Duh, because KVM needs to gain control in if there are multiple pending events.
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index aad3145b2f62fe..e891318595113e 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -1016,6 +1016,31 @@ int nested_svm_vmexit(struct vcpu_svm *svm) svm_switch_vmcb(svm, &svm->vmcb01); + /* Note about synchronizing some of int_ctl bits from vmcb02 to vmcb01: + * + * - V_IRQ, V_IRQ_VECTOR, V_INTR_PRIO_MASK, V_IGN_TPR: + * If the L2 doesn't intercept interrupts, then + * (even if the L2 does use virtual interrupt masking), + * KVM will use the vmcb02's V_INTR to detect interrupt window. + * + * In this case, the KVM raises the KVM_REQ_EVENT to ensure that interrupt window + * is not lost and this implicitly copies these bits from vmcb02 to vmcb01 + * + * V_TPR: + * If the L2 doesn't use virtual interrupt masking, then the L1's vTPR + * is stored in the vmcb02 but its value doesn't need to be copied from/to + * vmcb01 because it is copied from/to the TPR APIC's register on + * each VM entry/exit. + * + * V_GIF: + * - If the nested vGIF is not used, KVM uses vmcb02's V_GIF for L1's V_GIF, + * however, the L1 vGIF is reset to false on each VM exit, thus + * there is no need to copy it from vmcb02 to vmcb01. + */ + + if (!nested_exit_on_intr(svm)) + kvm_make_request(KVM_REQ_EVENT, &svm->vcpu); + if (unlikely(svm->lbrv_enabled && (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) { svm_copy_lbrs(vmcb12, vmcb02); svm_update_lbrv(vcpu);
If the L2 doesn't intercept interrupts, then the KVM will use vmcb02's V_IRQ for L1 (to detect the interrupt window) In this case on the nested VM exit KVM might need to copy the V_IRQ bit from the vmcb02 to the vmcb01, to continue waiting for the interrupt window. To make it simple, just raise the KVM_REQ_EVENT request, which execution will lead to the reenabling of the interrupt window if needed. Note that this is a theoretical bug because the KVM already does raise the KVM_REQ_EVENT request one each nested VM exit because the nested VM exit resets RFLAGS and the kvm_set_rflags() raises the KVM_REQ_EVENT request in the response. However raising this request explicitly, together with documenting why this is needed, is still preferred. Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com> --- arch/x86/kvm/svm/nested.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+)