From: Maxim Levitsky <mlevitsk@xxxxxxxxxx> If the L1 doesn't intercept interrupts, then the KVM will use vmcb02's V_IRQ for L1 (to detect an interrupt window) In this case on 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 KVM already does raise KVM_REQ_EVENT request on 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@xxxxxxxxxx> [reworded description as per Sean's v2 comment] Signed-off-by: Santosh Shukla <Santosh.Shukla@xxxxxxx> --- v3: Reworded commit description per Sean's v2 comment: https://lore.kernel.org/all/Y9RypRsfpLteK51v@xxxxxxxxxx/ 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 107258ed46ee..74e9e9e76d77 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -1025,6 +1025,31 @@ 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 L1 doesn't intercept interrupts, then + * (even if the L1 does use virtual interrupt masking), + * KVM will use the vmcb02's V_INTR to detect interrupt window. + * + * In this case, the KVM raises KVM_REQ_EVENT to ensure that interrupt + * window is not lost and KVM implicitly V_IRQ bit from vmcb02 to vmcb01 + * + * V_TPR: + * If the L1 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); -- 2.25.1
