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    SubjectRe: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention
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    On Thu, 2017-03-30 at 13:10 +0300, Stas Sergeev wrote:
    > 30.03.2017 08:14, Ricardo Neri пишет:
    > >>>> But at least dosemu implements it, so probably it is needed.
    > >>> Right.
    > >>>
    > >>>> Of course if it is used by one of 100 DOS progs, then there
    > >>>> is an option to just add its support to dosemu2 and pretend
    > >>>> the compatibility problems did not exist. :)
    > >>> Do you mean relaying the GP fault to dosemu instead of trapping it and
    > >>> emulating it in the kernel?
    > >> Yes, that would be optimal if this does not severely break
    > >> the current setups. If we can find out that smsw is not in
    > >> the real use, we can probably do exactly that.
    > >> But other
    > >> instructions are not in real use in v86 for sure, so I
    > >> wouldn't be adding the explicit test-cases to the kernel
    > >> that will make you depend on some particular behaviour
    > >> that no one may need.
    > >> My objection was that we shouldn't
    > >> write tests before we know exactly how we want this to work.
    > > OK, if only SMSW is used then I'll keep the emulation for SMSW only.
    > In fact, smsw has an interesting property, which is that
    > no one will ever want to disable its in-kernel emulation
    > to provide its own.
    > So while I'll try to estimate its usage, emulating it in kernel
    > will not be that problematic in either case.

    Ah good to know!

    > As for protected mode, if wine only needs sgdt/sidt, then
    > again, no one will want to disable its emulation. Not the
    > case with sldt, but AFAICS wine doesn't need sldt, and so
    > we can leave sldt without a fixups. Is my understanding
    > correct?

    This is my understanding as well. I could not find any use of sldt in
    wine. Alexandre, would you mind confirming?

    > In this case, I suppose, we are very well on a way to avoid
    > the extra syscalls to toggle the emulation features.

    Great! Then I will keep the emulation for sgdt, sidt, and smsw but not
    for str and sldt; for both vm86 and protected mode. This seems to be the
    agreement.

    Thanks and BR,
    Ricardo


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