virtualbox.org

TSU wrote:Because VBox possesses its own "virtualization interface code" independent of the OS,

Will this mean that if I run a HostOS which <does not> support any hypervisor but have the CPU virt extensions enabled in the BIOS, that Virtualbox will still be able to support hardware assisted virtualization and with 5.x also present a paravirtualization interface of choice to the Guest?

(Key here is that the OS specifically does not support virtualization so VBox essentially bypasses any OS non-support).

Yes, VirtualBox will use hardware virtualization if the host CPU supports it and it is available (i.e. not already used by something else). Whether the host OS has some built-in virtualization capabilities or not doesn't matter (with the caveat that the host OS may be taking over the hardware virtualization and then nothing else can use it).

Yes, VirtualBox can present a paravirtualization interface to the guest regardless of what the host OS can or can't do. Hyper-V for Windows guest on OS X or KVM for Linux hosts on Windows is no problem.

The paravirtualization interfaces in fact do not require hardware virtualization, there two are more or less orthogonal. A lot of the paravirtualization machinery was originally designed to improve virtualization performance on systems with no hardware virtualization. The interfaces are still useful but sometimes not as critical.