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
The following command works for me:
qemu-system-x86_64 -cpu host -kernel kernel/kernel -serial stdio -enable-kvm
-cpu host makes QEMU report host CPU features inside the VM (so your CPU must support vmx)
-enable-kvm is required by -cpu host
Even though according to this -cpu qemu64,+vmx should work, it doesn't work for me either.