[Info-vax] VMWARE/ESXi Linux

[Arne Vajhøj]

On 11/28/2024 8:24 AM, Dan Cross wrote:
> So Goldberg defined two "types" of hypervisor in his
> dissertation: Types 1 and 2.  Of course, this is an over
> simplification, and those of us who work on OSes and hypervisors
> understand that these distinctions are blurry and more on a
> continuum than hard and fast buckets, but to a first order
> approximation these categories are useful.
> 
> Roughly, a Type-1 hypervisor is one that runs on the bare metal
> and only supports guests; usually some special guest is
> designated as a trusted "root VM".  Xen, ESXi, and Hyper-V are
> examples of Type-1 hypervisors.
> 
> Again, roughly, a Type-2 hypervisor is one that runs in the
> context of an existing operating system, using its services and
> implementation for some of its functionality; examples include
> KVM (they _say_ it's type 1, but that's really not true) and
> PA1050.  Usually with a Type-2 HV you've got a userspace program
> running under the host operating system that provides control
> functionality, device models, and so on.  QEMU is an example of
> such a thing (sometimes, confusingly, this is called the
> hypervisor while the kernel-resident component, is called the
> Virtual Machine Monitor, or VMM), but other examples exist:
> CrosVM, for instance.

I think the relevant distinction is that type 1 runs in the
kernel while type 2 runs on the kernel.

KVM runs in Linux not on Linux. Which makes it type 1.

If VSI created a hypervisor as part of VMS then if
it was in SYS$SYSTEM it would be a type 2 while if it
was in SYS$LOADABLE_IMAGES it would be a type 1.

(the location of the EXE obviously doesn't matter, but
the location implies how it works)

QEMU is many things. I believe it can act both
as a CPU emulator, as a type 2 hypervisor and as
a control program for a type 1 hypervisor (KVM).

Arne