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    SubjectRe: [PATCH v3 04/12] Add "handle page fault" PV helper.
    On 01/21/2010 01:02 AM, Avi Kivity wrote:
    >>
    >> You can also just emulate the state transition -- since you know
    >> you're dealing with a flat protected-mode or long-mode OS (and just
    >> make that a condition of enabling the feature) you don't have to deal
    >> with all the strange combinations of directions that an unrestricted
    >> x86 event can take. Since it's an exception, it is unconditional.
    >
    > Do you mean create the stack frame manually? I'd really like to avoid
    > that for many reasons, one of which is performance (need to do all the
    > virt-to-phys walks manually), the other is that we're certain to end up
    > with something horribly underspecified. I'd really like to keep as
    > close as possible to the hardware. For the alternative approach, see Xen.
    >

    I obviously didn't mean to do something which didn't look like a
    hardware-delivered exception. That by itself provides a tight spec.
    The performance issue is real, of course.

    Obviously, the design of VT-x was before my time at Intel, so I'm not
    familiar with why the tradeoffs that were done they way they were.

    -hpa

    --
    H. Peter Anvin, Intel Open Source Technology Center
    I work for Intel. I don't speak on their behalf.



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