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Path: ...!weretis.net!feeder9.news.weretis.net!panix!.POSTED.spitfire.i.gajendra.net!not-for-mail From: cross@spitfire.i.gajendra.net (Dan Cross) Newsgroups: comp.os.vms Subject: Re: VMWARE/ESXi Linux Date: Tue, 3 Dec 2024 15:36:04 -0000 (UTC) Organization: PANIX Public Access Internet and UNIX, NYC Message-ID: <vin8h4$ntd$1@reader2.panix.com> References: <vi84pm$6ct6$4@dont-email.me> <slrnvkgb2b.2dr8a.mwilson@daenerys.home.mattwilson.org> <vi9qu1$ash$1@reader2.panix.com> <vin68p$3sjr$4@dont-email.me> Injection-Date: Tue, 3 Dec 2024 15:36:04 -0000 (UTC) Injection-Info: reader2.panix.com; posting-host="spitfire.i.gajendra.net:166.84.136.80"; logging-data="24493"; mail-complaints-to="abuse@panix.com" X-Newsreader: trn 4.0-test77 (Sep 1, 2010) Originator: cross@spitfire.i.gajendra.net (Dan Cross) Bytes: 2857 Lines: 43 In article <vin68p$3sjr$4@dont-email.me>, Arne Vajhøj <arne@vajhoej.dk> wrote: >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. No. They both run in supervisor mode. On x86, this is even necessary; the instructions to enter guest mode are privileged. Go back to Goldberg's dissertation; he discusses this at length. >KVM runs in Linux not on Linux. Which makes it type 1. Nope. KVM is dependent on Linux at this point. The claim that it is a type-1 hypervisor is predicated on the idea that it was separable from Linux, but I don't think anyone believes that anymore. - Dan C.