Pre-Virtualization: Slashing the cost of virtualization

Despite its current popularity, para-virtualization has an
enormous cost. Its
diversion from the platform architecture abandons many of the
benefits that come
with pure virtualization (the faithful emulation of the platform
API): stable and
well-defined platform interfaces, single binaries for kernel and
device drivers (and
thus lower testing, maintenance, and support cost), and vendor
independence.
These limitations are accepted as inevitable for significantly
better performance
and the ability to provide virtualization-like behavior on
non-virtualizable
hardware, such as x86.

We argue that the above limitations are not inevitable, and
present pre-
virtualization, which preserves the benefits of full
virtualization without sacrificing
the performance benefits of para-virtualization. In a
semi-automatic step an OS is
prepared for virtualization. The required modifications are
orders of magnitudes
smaller than for para-virtualization. A virtualization module,
that is collocated with
the guest OS, transforms the standard platform API into the
respective hypervisor
API. The guest OS is still programmed against a common
... mehr
architecture, and the
binary remains fully functional on bare hardware. The support of
a new hypervisor
or updated interface only requires the implementation of a
single interface
mapping. We validated our approach for a variety of hypervisors,
on two very
different hardware platforms (x86 and Itanium), with multiple
generations of Linux
as guests. We found that pre-virtualization achieves essentially
the same
performance as para-virtualization, at a fraction of the
engineering cost.