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    SubjectRe: [patch] lazy TSS's I/O bitmap copy ...
    On Mon, 23 Aug 2004, Linus Torvalds wrote:

    > On Mon, 23 Aug 2004, Davide Libenzi wrote:
    > >
    > > The eventually double GPF would happen only on TSS-IObmp-lazy tasks, ie
    > > tasks using the I/O bitmap.
    > You could also check for the error code (at least the low 16 bits) being
    > 0, I guess, just to cut down the noise.

    Yep, that's right there available.

    > > The check for the I/O opcode can certainly be
    > > done though, even if it'd make the code a little bit more complex.
    > Have to be very careful there to avoid nasty security issues. And with
    > ins/outs, you can have various prefixes etc, so decoding is not as trivial
    > as it could otherwise be. Even the regular in/out can have a data size
    > overrides..
    > in/out is also commonly used from vm86 mode, so decoding it really needs
    > to get all of the segmentation base crap right too. Nasty nasty nasty.
    > In short, I think that if we do this at all, I'd much rather just do the
    > simple "trap twice" thing that Davide did. It's too easy to get it wrong
    > otherwise.

    IMHO since the GPF path is not a fast path like a page fault, we shouldn't
    be in bad shape with the current approach. No?

    - Davide

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