I read from here that vmx capability support on QEMU must be explicitly enabled by providing the +vmx option to the command but the problem is that it does not seem to work. In
No, the vmx flag is not supported in the processor emulation mode of QEMU. In order to use vmx in QEMU, you must use KVM with QEMU (replacing -no-kvm with -enable-kvm); and your host processor must support vmx.
In this document it shows the nested vmx instructions support in the Linux KVM; meaning this feature must be used with -enable-kvm.
In my test the options -enable-kvm -cpu kvm64,+vmx work, as the vmx feature is detected in the guest OS.