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    SubjectRe: Simple patches for Linux as a guest OS in a plex86 VM (please consider)
    On Fri, 24 Jan 2003 08:52:46 PST, Kevin Lawton said:

    > About 99% of the work of a full x86 VM is on handling less
    > than 1% of the cases. So the new plex86 angle is, forget doing
    > all the fancy work for 1%. If you're running a VM friendly OS
    > (like Linux with my small patches), you end up with a potentially high
    > performance and Open Source VM, with very little work.

    One of the first implementations of VM was by IBM, called CP/67. It
    eventually evolved into VM/370 and its follow-ons.

    The initial design reason for CP/67 was to allow 2 or more MVS development
    teams to share a system for testing, so the other team could keep working
    while the first team debugged a system crash with tools better than the
    lights-n-switches at the console.

    It turns out that the 99% of the work to cover the 1% of the cases is really
    important. The usual reason for doing VM is to isolate images from each other
    - and if you don't cover that last 1%, a programming error in one of the images
    can nuke your supervisor code into oblivion. It may be a "VM friendly OS like
    Linux", but it can still oops in strange ways. For starters, what happens
    if you run a Linux *without* your patches under plex86? ;)

    Now if you think about it, and not covering the 1% case is deemed acceptable,
    that's OK too. But it's something that needs to be considered.
    Valdis Kletnieks
    Computer Systems Senior Engineer
    Virginia Tech

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