> Within the guest I run a BSD guest OS that returns from certain system > calls using the IRET instruction. > > Do you have any thoughts on where I could be wrong? No, but I suggest using a small unit test in kvm-unit-tests https://www.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git/ (either vmx.flat to test the VMX settings, or a test using IRET to test your modified KVM). Tracing the unit test with trace-cmd can provide clues more easily. Paolo
