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    SubjectRe: Sysenter crash with Nested Task Bit set
    Linus Torvalds wrote:
    > Final note (I promise): now that we save/restore eflags again, we
    > should probably revert the set_iopl_mask() in task switching too. However,
    > that apparently has some para-virtualization issues, so I'm going to
    > ignore that part from now.

    I'm wondering if we shouldn't have a (__)switch_to paravirt hook, so we
    can wrap the context switch in whatever we like.

    > However, I'd really like people who know and care about the
    > paravirtualization to take a good long look at it: because right now, with
    > the addition of the eflags save/restore, the set_iopl_mask() in
    > __switch_to() is entirely useless for non-virtualized environments, afaik.

    Hm. Zach removed the pushf/popf in switch_to this last Sept, with the
    comment "The pushf/popf in switch_to are ONLY used to switch IOPL.
    Making this explicit in C code is more clear. This pushf/popf pair was
    added as a bugfix for leaking IOPL to unprivileged processes when using
    sysenter/sysexit based system calls (sysexit does not restore flags)."

    > Zack added to the cc. Who else needs to know?
    Rusty, Chris Wright and me.

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      Last update: 2006-09-18 18:27    [W:0.024 / U:1.060 seconds]
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