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    SubjectRe: [patch 47/60] x86/ldt: Map LDT entries into fixmap
    On Mon, 4 Dec 2017, Andy Lutomirski wrote:

    > On Mon, Dec 4, 2017 at 6:07 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
    > > From: Thomas Gleixner <tglx@linutronix.de>
    > >
    > > LDT is not really commonly used on 64bit so the overhead of populating the
    > > fixmap entries on context switch for the rare LDT syscall users is a
    > > reasonable trade off vs. having extra dynamically managed mapping space per
    > > process.
    > >
    >
    > Hmm, I wonder just how slow this is. It might be okay. It's
    > certainly not the way I imagined it working.

    I know, it was the laziest way I could come up with. The only nasty thing
    here is that __set_fixmap() does a tlb flush which is pointless as that
    happens anyway. On my todo list was a noflush variant for set_fixmap along
    with a variant which takes a whole range. That would simplify other places
    as well. Though with the plan to map that stuff to a different place we
    actually can avoid the weirdness of fixmaps

    Thanks,

    tglx

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