This means that the personality can emulate breakpoints and
singlesteps in userspace threads, on behalf of the generic
OS Process overlay driver.  Thus, the OS Process driver can
now be stacked atop the KVM/QEMU driver with real breakpoints.
Previously, it could be stacked atop KVM/QEMU, but without
userspace breakpoints... so it wasn't especially useful for
active debugging.

The OS Process driver was previously only able to stack atop
the Xen driver, because the Xen driver supported hacked
hypervisors that would divert userspace debug exceptions to
the driver (as well as kernel debug exceptions).  Hacking
QEMU's GDB stub to do this was undesireable, and infeasible.
(The QEMU/KVM support was built through the GDB driver, because
QEMU provides a GDB server stub --- but supporting userspace
breakpoints in an overlay driver atop our GDB driver was
infeasible due to the "shared page" breakpoint issue.  The
shared page issue occurs when we place a ...